Junio de 2016
Two-stage composite megathrust rupture of the 2015 Mw8.4 Illapel, Chile, earthquake identified by spectral-element inversion of teleseismic waves
Authors: Shiann-Jong Lee, Te-Yang Yeh et al
Link: Click here
Abstract
The Mw8.4 Illapel earthquake occurred on 16 September was the largest global event in 2015. This earthquake was not unexpected because the hypocenter was located in a seismic gap of the Peru-Chile subduction zone. However, the source model derived from 3-D spectral-element inversion of teleseismic waves reveals a distinct |
two-stage rupture process with completely different slip characteristics as a composite megathrust event. The two stages were temporally separated. Rupture in the first stage, with a moment magnitude of Mw8.32, built up energetically from the deeper locked zone and propagated in the updip direction toward the trench. Subsequently, the rupture of the second stage, with a magnitude of Mw8.08, mainly occurred in the shallow subduction zone with atypical repeating slip behavior. The unique spatial-temporal rupture evolution presented in this source model is key to further in-depth studies of earthquake physics and source dynamics in subduction systems. |
Junio de 2016
Deeper penetration of large earthquakes on seismically quiescent faults
Authors: Junle Jiang and Nadia Lapustal
Link: Click here
Abstract
Why many major strike-slip faults known to have had large earthquakes are silent in the interseismic period is a long-standing enigma. One would expect small earthquakes to occur at least at the bottom of the seismogenic zone, where deeper aseismic deformation concentrates loading. We suggest that the absence of such concentrated microseismicity indicates deep rupture past the seismogenic zone in previous large earthquakes. We support this conclusion with numerical simulations of fault behavior and observations of recent major events. Our modeling implies that the 1857 Fort Tejon earthquake on the San Andreas Fault in Southern California penetrated below the seismogenic zone by at least 3 to 5 kilometers. Our findings suggest that such deeper ruptures may occur on other major fault segments, potentially increasing the associated seismic hazard.
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A microseismic turn off
Certain strike-slip faults do not have the expected number of microearthquakes between larger earthquakes. Jiang and Lapusta suggest that this behavior is down to what the last big earthquake looked like. They found that microseismicity turns off if an earthquake's rupture runs deeper than the fault's locking depth. This appears to be the case along the famous San Andreas Fault and also along other strike-slip faults around the world. The discovery may allow for better estimates of historic earthquake magnitudes and improve hazard assessments.
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Junio de 2016
Simulating 2 Ga of geodynamo history
Author: Peter E. Driscoll
Link: Click here
Abstract
The paleomagnetic record indicates the geodynamo has been active over much of Earth history with surprisingly little trend in paleointensity. Variability, however, is expected from models that predict a sharp increase in intensity following inner core nucleation (ICN) and implied by Neoproterozoic anomalies that hint at a highly variable field over several hundred million
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years. Here we demonstrate with a suite of numerical dynamos driven by a new thermal evolution model that the geodynamo could have transitioned from a multipolar to dipolar regime around 1.7 Ga, then to a weak-field dynamo around 1.0 Ga, and finally to a strong-field dipole following ICN around 650 Ma that is maintained to the present day. The occurrence of a weak-field geodynamo in the Neoproterozoic may be consistent with the observed anomalous apparent polar wander paths and reversal behavior. Recovery to a dipolar geodynamo in the Phanerozoic could be a signature of inner core nucleation. Index terms: 1507, 1560, and 1521. |
Junio de 2016
Dynamic rupture processes inferred from laboratory microearthquakes
Authors: François. X. Passelègue, Alexandre Schubnel et al
Link: Click here
Abstract
We report macroscopic stick-slip events in saw-cut Westerly granite samples deformed under controlled upper crustal stress conditions in the laboratory. Experiments were conducted under triaxial loading (σ1>σ2=σ3) at confining pressures (σ3) ranging from 10 to 100 MPa. A high-frequency acoustic monitoring array recorded particle acceleration during macroscopic stick-slip events allowing us to estimate rupture speed. In addition, we record the stress drop dynamically and we show that the dynamic stress drop measured
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locally close to the fault plane is almost total in the breakdown zone (for normal stress >75 MPa), while the friction f recovers to values of f > 0.4 within only a few hundred microseconds. Enhanced dynamic weakening is observed to be linked to the melting of asperities which can be well explained by flash heating theory in agreement with our postmortem microstructural analysis. Relationships between initial state of stress, rupture velocities, stress drop, and energy budget suggest that at high normal stress (leading to supershear rupture velocities), the rupture processes are more dissipative. Our observations question the current dichotomy between the fracture energy and the frictional energy in terms of rupture processes. A power law scaling of the fracture energy with final slip is observed over 8 orders of magnitude in slip, from a few microns to tens of meters. |
Junio de 2016
Strain rate dependency of oceanic intraplate earthquake b-values at extremely low strain rates
Authors: Ryohei Sasajima and Takeo Ito
Link: Click here
Abstract
We discovered a clear positive dependence of oceanic intraplate earthquake (OCEQ) b-values on the age of the oceanic lithosphere. OCEQ b-values in the youngest (<10 Ma) oceanic lithosphere are around 1.0, while those in middle to old (>20 Ma) oceanic lithosphere exceed 1.5, which is significantly higher than the average worldwide earthquake b-value (around 1.0). On the other hand, the b-value of intraplate earthquakes in the Ninety East-Sumatra orogen, where oceanic lithosphere has an anomalously
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higher strain rate compared with normal oceanic lithosphere, is 0.93, which is significantly lower than the OCEQ b-value (about 1.9) with the same age (50–110 Ma). Thus, the variation in b-values relates to the strain rate of the oceanic lithosphere and is not caused by a difference in thermal structure. We revealed a negative strain rate dependency of the b-value at extremely low strain rates (<2 × 10−10/year), which can clearly explain the above b-values. We propose that the OCEQ b-value depends strongly on strain rate (either directly or indirectly) at extremely low strain rates. The high OCEQ b-values (>1.5) in oceanic lithosphere >20 Ma old imply that future improvement in seismic observation will capture many smaller magnitude OCEQs, which will provide valuable information on the evolution of the oceanic lithosphere and the driving mechanism of plate tectonics. |
Junio de 2016
Combination of various observation techniques for regional modeling of the gravity field
Authors: Verena Lieb, Michael Schmidt et al
Link: Click here
Abstract
Modeling a very broad spectrum of the Earth's gravity field needs observations from various measurement techniques with different spectral sensitivities. Typically, high-resolution regional gravity data are combined with low-resolution global observations. To exploit the gravitational information as optimally as possible, we set up a regional modeling approach using radial spherical basis functions, emphasizing the strengths of various data sets by the flexible combination of high- and middle-resolution terrestrial, airborne, shipborne, and altimetry measurements. The basis functions are defined and located in the region of interest in such a
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manner, which the highest measure of information of the input data is captured. Any functional of the Earth's gravity field can be derived, as, e.g., quasi-geoid heights or gravity anomalies. Here we present results of a study area in Northern Germany. A comprehensive cross validation to external observation data delivers standard deviations less than 5 cm. Differences to an existing regional quasi-geoid model count on average ±6 cm and proof the plausibility of our solution. The comparison with existing global models reaches higher standard deviations for the more sensitive gravity anomalies as for quasi-geoid heights, showing the additional value of our solution in the high frequency domain. Covering a broad frequency spectrum, our regional models can be used as basis for various applications, such as refinement of global models, national geoid determination, and detection of mass anomalies in the Earth's interior. |
Junio de 2016
Two-stage composite megathrust rupture of the 2015 Mw8.4 Illapel, Chile, earthquake identified by spectral-element inversion of teleseismic waves
Authors: Shiann-Jong Lee, Te-Yang Yeh et al
Link: Click here
Abstract
The Mw8.4 Illapel earthquake occurred on 16 September was the largest global event in 2015. This earthquake was not unexpected because the hypocenter was located in a seismic gap of the Peru-Chile subduction zone. However, the source model derived from 3-D spectral-element inversion of teleseismic waves reveals a distinct
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two-stage rupture process with completely different slip characteristics as a composite megathrust event. The two stages were temporally separated. Rupture in the first stage, with a moment magnitude of Mw8.32, built up energetically from the deeper locked zone and propagated in the updip direction toward the trench. Subsequently, the rupture of the second stage, with a magnitude of Mw8.08, mainly occurred in the shallow subduction zone with atypical repeating slip behavior. The unique spatial-temporal rupture evolution presented in this source model is key to further in-depth studies of earthquake physics and source dynamics in subduction systems. |
Junio de 2016
Extraordinary sediment delivery and rapid geomorphic response following the 2008–2009 eruption of Chaitén volcano, Chile
Authors: Jon J. Major, Daniel Bertin et al
Link: Click here
Abstract
The 10-day explosive phase of the 2008–2009 eruption of Chaitén volcano, Chile, draped adjacent watersheds with a few cm to >1 m of tephra. Subsequent lava-dome collapses generated pyroclastic flows that delivered additional sediment. During the waning phase of explosive activity, modest rainfall triggered an extraordinary sediment flush which swiftly aggraded multiple channels by many meters. Ten km from the volcano, Chaitén River channel aggraded 7 m and the river avulsed through a coastal town. That aggradation and delta growth below the abandoned and avulsed channels allow estimates of post-disturbance traction-load
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transport rate. On the basis of pre-eruption bathymetry and remotely sensed measurements of delta-surface growth, we derived a time series of delta volume. The initial flush from 11 to 14 May 2008 deposited 0.5–1.5 million m3 of sediment at the mouth of Chaitén River. By 26 May, after channel avulsion, a second delta amassed about 2 million m3 of sediment; by late 2011 it amassed about 11 million m3. Accumulated sediment consists of low-density vesicular pumice and lithic rhyolite sand. Rates of channel aggradation and delta growth, channel width, and an assumed deposit bulk density of 1100–1500 kg m−3 indicate mean traction-load transport rate just before and shortly after avulsion (∼14–15 May) was very high, possibly as great as several tens of kg s−1 m−1. From October 2008 to December 2011, mean traction-load transport rate declined from about 7 to 0.4 kg −1 m−1. Despite extraordinary sediment delivery, disturbed channels recovered rapidly (a few years). |
Junio de 2016
Can we manage groundwater? A method to determine the quantitative testability of groundwater management plans
Authors: E. K. White, T. J. Peterson et al
Link: Click here
Abstract
Groundwater is the world's largest freshwater resource and due to over-extraction, levels have declined in many regions causing extensive social and environmental impacts. Groundwater management seeks to balance and mitigate the detrimental impacts of development and plans are commonly used to outline management pathways. Thus, plan efficiency is crucial, but seldom are plans systematically and quantitatively assessed for effectiveness. This study frames groundwater management as a system control problem in order to develop a novel testability assessment rubric to determine if plans meet the |
requirements of a control loop, and subsequently, whether they can be quantitatively tested. Seven components of a management plan equivalent to basic components of a control loop were determined, and requirements of each component necessary to enable testability were defined. Each component was weighted based upon proposed relative importance, then segmented into rated categories depending on the degree the requirements were met. Component importance varied but, a defined objective or acceptable impact was necessary for plans to be testable. The rubric was developed within the context of the Australian groundwater management industry, and while use of the rubric is not limited to Australia, it was applied to 15 Australian groundwater management plans and approximately 47% were found to be testable. Considering the importance of effective groundwater management, and the central role of plans, our lack of ability to test many plans is concerning. |
Junio de 2016
Seismic velocity structure of the Juan de Fuca and Gorda plates revealed by a joint inversion of ambient noise and regional earthquakes
Author: Haiying Gao
Link: Click here
Abstract
The crust and upper mantle seismic structure, spanning from the Juan de Fuca and Gorda spreading centers to the Cascade back arc, is imaged with full-wave propagation simulation and a joint inversion of ambient noise and regional earthquake recordings. The spreading centers have anomalously low shear wave velocity
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beneath the oceanic lithosphere. Around the Cobb axial seamount, we observe a low-velocity anomaly underlying a relatively thin oceanic lithosphere, indicating its influence on the Juan de Fuca ridge. The oceanic Moho is clearly defined by a P velocity increase from 6.3 km/s to 7.5 km/s at about 6 km depth beneath the seafloor. The thickness of the oceanic plates is less than 40 km prior to subduction, and the structure of the oceanic lithosphere varies both along strike and along dip. Farther landward, very low velocity anomalies are observed above the plate interface along the Cascade fore arc, indicative of subducted sediments. |
Junio de 2016
Lagrangian flow measurements and observations of the 2015 Chilean tsunami in Ventura, CA
Authors: Nikos Kalligeris, Vassilios Skanavis et al
Link: Click here
Abstract
Tsunami-induced coastal currents are spectacular examples of nonlinear and chaotic phenomena. Due to their long periods, tsunamis transport substantial energy into coastal waters, and as this energy interacts with the ubiquitous irregularity of bathymetry, shear and turbulent features appear. The oscillatory character of a tsunami wave train leads to flow reversals, which in principle can spawn persistent turbulent coherent structures (e.g., large vortices or “whirlpools”) that can dominate damage and
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transport potential. However, no quantitative measurements exist to provide physical insight into this kind of turbulent variability, and no motion recordings are available to help elucidate how these vortical structures evolve and terminate. We report our measurements of currents in Ventura Harbor, California, generated by the 2015 Chilean M8.3 earthquake. We measured surface velocities using GPS drifters and image sequences of surface tracers deployed at a channel bifurcation, as the event unfolded. From the maps of the flow field, we find that a tsunami with a near-shore amplitude of 30 cm at 6 m depth produced unexpectedly large currents up to 1.5 m/s, which is a fourfold increase over what simple linear scaling would suggest. Coherent turbulent structures appear throughout the event, across a wide range of scales, often generating the greatest local currents. |
Junio de 2016
The importance of earthquake interactions for injection-induced seismicity: Retrospective modeling of the Basel Enhanced Geothermal System
Authors: Flaminia Catalli, Antonio P. Rinaldi et al
Link: Click here
Abstract
We explore the role of earthquake interactions during an injection-induced seismic sequence. We propose a model, which considers both a transient pressure and static stress redistribution due to event interactions as triggering mechanisms. By calibrating the model against
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observations at the Enhanced Geothermal System of Basel, Switzerland, we are able to reproduce the time behavior of the seismicity rate. We observe that considering earthquake interactions in the modeling leads to a larger number of expected seismic events (24% more) if compared to a pressure-induced seismicity only. The increase of the number of events is particularly evident after the end of the injection. We conclude that implementing a model for estimating the static stress changes due to mutual event interactions increases significantly the understanding of the process and the behavior of induced seismicity. |
Junio de 2016
Evidence of underground electric current generation during the 2009 L'Aquila earthquake - real or instrumental?
Authors:
F. Masci, J. N. Thomas
et al
Link: Click here
Abstract
We investigate magnetic effects in correspondence of the MW6.1 L'Aquila earthquake. Magnetic and seismic records are analysed. Rapid and distinct changes and an offset can be seen in magnetic field components after the main shock. We show that these effects result from electromagnetic induction due to the |
movement of the sensors through the Earth's magnetic field and from a permanent displacement of the sensors from their original position caused by the passing seismic waves. A transient signal in total field data from an overhauser magnetometer apparently occurs in correspondence with the earthquake. Our analysis shows that the transient was not observed by other sensors that were operating in close proximity to the overhauser. Thus, the transient signal in the total magnetic field data, and the offset in the magnetic field components, cannot be associated with a hypothetical underground electric current generated by the earthquake, as suggested by Nenovski (2015). |
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Mayo de 2016
Nature of the seismic lithosphere-asthenosphere boundary within normal oceanic mantle from high-resolution receiver functions
Authors: Tolulope Morayo Olugboji, Jeffrey Park et al
Link: Click here
Abstract
Receiver function observations in the oceanic upper mantle can test causal mechanisms for the depth, sharpness, and age dependence of the seismic wave speed decrease thought to mark the lithosphere-asthenosphere boundary (LAB). We use a combination of frequency-dependent harmonic decomposition of receiver functions and synthetic forward modeling to provide new seismological constraints on this “seismic LAB” from 17 ocean-bottom stations and 2 borehole stations in the Philippine Sea and northwest Pacific Ocean. Underneath young oceanic crust, the seismic LAB depth follows the ∼1300 K isotherm but a lower isotherm (∼1000 K) is suggested in the Daito ridge, the Izu-Bonin-Mariana trench, and the northern Shikoku basin. Underneath old oceanic crust, the seismic LAB |
lies at a constant depth 70 km. The age dependence of the seismic LAB depth is consistent with either a transition to partial-melt conditions or a subsolidus rheological change as the causative factor. The age dependence of interface sharpness provides critical information to distinguish these two models. Underneath young oceanic crust, the velocity gradient is gradational, while for old oceanic crust, a sharper velocity gradient is suggested by the receiver functions. This behavior is consistent with the prediction of the subsolidus model invoking anelastic relaxation mediated by temperature and water content, but is not readily explained by a partial-melt model. The Ps conversions display negligible two-lobed or four-lobed back azimuth dependence in harmonic stacks, suggesting that a sharp change in azimuthal anisotropy with depth is not responsible for them. We conclude that these ocean-bottom observations indicate a subsolidus elastically accommodated grain-boundary sliding (EAGBS) model for the seismic LAB. Because EAGBS does not facilitate long-term ductile deformation, the seismic LAB may not coincide with the conventional transition from lithosphere to asthenosphere corresponding to a change in the long-term rheological properties. |
Mayo de 2016
Systematic correlations of the earthquake frequency-magnitude distribution with the deformation and mechanical regimes in the Taiwan orogen
Authors: Yen-Ling Chen, Shu-Huei Hung
et al
Link: Click here
Abstract
We investigate the correlation of the earthquake frequency-magnitude distribution with the
style of faulting and stress in Taiwan. The b-values estimated for three types of focal
mechanisms show significant differences with the lowest for thrust, intermediate for strikeslip,
and highest value for normal events, consistent |
with those found in global and other
regional seismicity. Lateral distribution of the b- values shows a good correlation with the
predominant faulting mechanism, crustal deformation and stress patterns. The two N-S
striking thrust zones in western and eastern Taiwan under the larger E-W shortening and
differential stress yield the lower b-values than those in the in-between mountain ranges
subject to the smaller extensional stress and dominated by strike-slip and normal faults. The
termination of the monotonically decreasing b-value with depth at ~15-20 km corroborates its
inverse relationship with stress and the existence of the brittle-plastic transition in the weak
middle crust beneath the Taiwan orogen. |
Mayo de 2016
Simulating Two Billion Years of Geodynamo History
Author: Peter E. Driscoll
Link: Click here
Abstract
The paleomagnetic record indicates the geodynamo has been active over much of Earth history with surprisingly little trend in paleointensity. Variability, however, is expected from models that predict a sharp increase in intensity following inner core nucleation (ICN) and implied by Neoproterozoic anomalies that hint at a
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highly variable field over several hundred Myr. Here we demonstrate with a suite of numerical dynamos driven by a new thermal evolution model that the geodynamo could have transitioned from a multipolar to dipolar regime around 1.7 Ga, then to a weak-field dynamo around 1.0 Ga, and finally to a strong-field dipole following ICN around 650 Ma that is maintained to the present-day. The occurrence of a weak-field geodynamo in the Neoproterozoic may be consistent with the observed anomalous apparent polar wander paths and reversal behavior. Recovery to a dipolar geodynamo in the Phanerozoic could be a signature of inner core nucleation. |
Mayo de 2016
A mass balance and isostasy model: Exploring the interplay between magmatism, deformation, and surface erosion in continental arcs using central Sierra Nevada as a case study
Authors: Wenrong Cao and Scott Paterson
Link: Click here
Abstract
A one-dimensional mass balance and isostasy model is used to explore the feedbacks between magmatism, deformation and surface erosion and how they together affect crustal thickness, elevation, and exhumation in a continental arc. The model is applied to central Sierra Nevada in California by parameterizing magma volume and deformational strain. The simulations capture the first-order Mesozoic-Cenozoic histories of crustal thickness, elevation and erosion including |
moderate Triassic crustal thickening and Jurassic crustal thinning followed by a strong Cretaceous crustal thickening, the latter resulting in a 60-70-km-thick crust plus a 20-km-thick arc eclogitic root, and a ∼5 km elevation in the Late Cretaceous. The contribution of contractional deformation to the crustal thickening is twice that of the magmatism. The contribution to elevation from magmatism is dampened by the formation of an eclogitic root. Erosion rate increases with the magnitude of crustal thickening (by magmatism and deformation) but its peak rate always lags behind the peak rate of thickening. We propose that thickened crust initially promotes magma generation by downward transport of materials to the magma source region, which may eventually jam the mantle wedge affecting the retro-arc underthrusting process and reducing arc magmatism. |
Mayo de 2016
Comparing source inversion techniques for GPS-based local tsunami forecasting: A case study for the April 2014 M8.1 Iquique, Chile, earthquake
Authors: Kejie Chen, Andrey Babeyko et al
Link: Click here
Abstract
Real-time GPS is nowadays considered as a valuable component of next generation near-field tsunami early warning systems able to provide fast and reliable source parameters. Looking for optimal methodologies and assessing corresponding uncertainties becomes an important task. We take the opportunity and |
consider the 2014 Pisagua event as a case study to explore tsunami forecast uncertainty related to the GPS-based source inversion. We intentionally neglect all other sources of uncertainty (observation set, signal processing, wave simulation, etc.) and exclusively assess the effect of inversion technique. In particular, we compare three end-member methods: (1) point-source fastCMT (centroid moment tensor), (2) distributed slip along predefined plate interface, and (3) unconstrained inversion into a single uniform slip finite fault. The three methods provide significantly different far-field tsunami forecast but show surprisingly similar tsunami predictions in the near field. |
Mayo de 2016
Tsunami earthquake can occur elsewhere along the Japan Trench—Historical and geological evidence for the 1677 earthquake and tsunami
Author: H. Yanagisawa, K. Goto et al
Link: Click here
Abstract
Since the 11 March 2011 Tohoku earthquake, the mechanisms of large earthquakes along the Japan Trench have been intensely investigated. However, characteristics of tsunami earthquakes, which trigger unusually large tsunami, remain unknown. The earthquake of 4 November 1677 was a tsunami earthquake striking the southern part of the Japan Trench. Its source mechanism remains unclear. This study elucidates the fault slip and moment magnitude of the 1677 earthquake and tsunami based on integrated analyses of historical documents, tsunami deposits, and numerical simulation. Geological survey results, the analytical results of thickness |
and grain size distributions and diatoms, revealed that tsunami deposits in a small pond at 11 m elevation were probably formed by the 1677 event. This finding and historical descriptions are useful as important constraint conditions to estimate unusually large fault slips and moment magnitude of the 1677 earthquake. Numerical simulation results reveal that 8.34–8.63 moment magnitude with the large 11–16 m slip area is necessary to satisfy the constraint conditions. This fault slip and magnitude are equivalent to those of the 1896 Sanriku earthquake: a well-known tsunami earthquake in the northern part of the Japan Trench. We therefore conclude that a tsunami earthquake of moment magnitude 8.3–8.6 with unusually large slip can occur elsewhere along the Japan Trench. This point should be considered for future tsunami risk assessment along the Japan Trench and along any trench having similar tectonic settings to those of the Japan Trench. |
Mayo de 2016
The damage is done: Low fault friction recorded in the damage zone of the shallow Japan Trench décollement
Author: Tucker T. Keren, James D. Kirkpatrick et al
Link: Click here
Abstract
Fault damage zones record the integrated deformation caused by repeated slip on faults and reflect the conditions that control slip behavior. To investigate the Japan Trench décollement, we characterized the damage zone close to the fault from drill core recovered during Integrated Ocean Drilling Program Expedition 343 (Japan Trench Fast Drilling Project (JFAST)). Core-scale and microscale structures include phyllosilicate bands, shear fractures, and joints. They are most abundant near the décollement and decrease in density sharply above and below the fault. Power law fits describing the change in structure density |
with distance from the fault result in decay exponents (n) of 1.57 in the footwall and 0.73 in the hanging wall. Microstructure decay exponents are 1.09 in the footwall and 0.50 in the hanging wall. Observed damage zone thickness is on the order of a few tens of meters. Core-scale structures dip between ~10° and ~70° and are mutually crosscutting. Compared to similar offset faults, the décollement has large decay exponents and a relatively narrow damage zone. Motivated by independent constraints demonstrating that the plate boundary is weak, we tested if the observed damage zone characteristics could be consistent with low-friction fault. Quasi-static models of off-fault stresses and deformation due to slip on a wavy, frictional fault under conditions similar to the JFAST site predict that low-friction fault produces narrow damage zones with no preferred orientations of structures. These results are consistent with long-term frictional weakness on the décollement at the JFAST site. |
Mayo de 2016
The 2015 Mw 7.1 earthquake on the charlie-gibbs transform fault: repeating earthquakes and multi-modal slip on a slow oceanic transform
Authors: K. Aderhold and R. E. Abercrombie
Link: Click here
Abstract
The 2015 MW 7.1 earthquake on the Charlie-Gibbs transform fault along the Mid-Atlantic Ridge is the latest in a series of seven large earthquakes since 1923. We propose that these earthquakes form a pair of quasi-repeating sequences with the largest magnitudes and longest repeat times for such sequences
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observed to date. We model teleseismic body waves and find that the 2015 earthquake ruptured a distinct segment of the transform from the previous 1998 earthquake. The two events display similarities to earthquakes in 1974 and 1967 respectively. We observe large oceanic transform earthquakes to exhibit characteristic slip behavior, initiating with small slip near the ridge, and propagating unilaterally to significant slip asperities nearer the center of the transform. These slip distributions combined with apparent segmentation support multimode slip behavior with fault slip accommodated both seismically during large earthquakes and aseismically in between. |
Mayo de 2016
Identifying remnants of early Earth
Author: Tais W. Dahl
Link: Click here
Abstract
The chemical composition of Earth's mantle can tell us how our planet formed and how subsequent mantle dynamics have since homogenized the mantle through convective processes. Most terrestrial rocks have a similar tungsten (W) isotope composition (1), but some rocks that have been dated at 2.8 Ga (billion years old) (2), 3.8 Ga (3), and 3.96 Ga (4) have elevated |
182W/184W ratios. This is reported as µ182W, in parts per million (ppm) deviation from the bulk silicate Earth. Until now, the outliers have included only these ancient rock samples with a small µ182W excess (≤15 ppm) that can be attributed to the final ∼0.5% of Earth's mass that accreted late in its accretion history. On page 809 of this issue, Rizo et al. (5) report W isotope data from young mantle-derived rocks with µ182W excesses of 10 to 48 ppm. This result is spectacular because the range of µ182W values in mantle-derived rocks is larger than can be accommodated by late accretion; the implication is that remnants of Earth's earliest mantle have been preserved over the entirety of Earth's history. |
Mayo de 2016
Preservation of Earth-forming events in the tungsten isotopic composition of modern flood basalts
Authors: Hanika Rizo1, Richard J. Walker et al
Link: Click here
Abstract
Details about how Earth formed are gleaned from the daughter products of certain short-lived radioactive isotopes found in rocks. Rizo et al. describe subtle tungsten isotope variations in rocks from the very deep mantle in Baffin Island and the Ontong Java Plateau (see the Perspective by Dahl). The results suggest that portions of Earth have remained unmixed since it formed. The unmixed deep mantle rocks also imply that Earth's core formed from several large impact events.
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How much of Earth's compositional variation dates to processes that occurred during planet formation remains an unanswered question. High-precision tungsten isotopic data from rocks from two large igneous provinces, the North Atlantic Igneous Province and the Ontong Java Plateau, reveal preservation to the Phanerozoic of tungsten isotopic heterogeneities in the mantle. These heterogeneities, caused by the decay of hafnium-182 in mantle domains with high hafnium/tungsten ratios, were created during the first ~50 million years of solar system history, indicating that portions of the mantle that formed during Earth’s primary accretionary period have survived to the present. |
Mayo de 2016
Reflection imaging of the Moon's interior using deep-moonquake seismic interferometry
Authors: Yohei Nishitsuji, C. A. Rowe et al
Link: Click here
Abstract
The internal structure of the Moon has been investigated over many years using a variety of seismic methods, such as travel time analysis, receiver functions, and tomography. Here we propose to apply body-wave seismic interferometry to deep moonquakes in order to retrieve zero-offset reflection responses (and thus images) beneath the Apollo stations on the nearside of the Moon from virtual sources |
colocated with the stations. This method is called deep-moonquake seismic interferometry (DMSI). Our results show a laterally coherent acoustic boundary around 50 km depth beneath all four Apollo stations. We interpret this boundary as the lunar seismic Moho. This depth agrees with Japan Aerospace Exploration Agency's (JAXA) SELenological and Engineering Explorer (SELENE) result and previous travel time analysis at the Apollo 12/14 sites. The deeper part of the image we obtain from DMSI shows laterally incoherent structures. Such lateral inhomogeneity we interpret as representing a zone characterized by strong scattering and constant apparent seismic velocity at our resolution scale (0.2–2.0 Hz). |
Mayo de 2016
Analysis of Traveling Ionospheric Disturbances (TIDs) in GPS TEC Launched by the 2011 Tohoku Earthquake
Authors: Geoff Crowley, Irfan Azeem et al
Link: Click here
Abstract
TIDs have been detected using various measurement techniques, including HF sounders, incoherent scatter radars, in-situ measurements, and optical techniques. However, observations of TIDs have tended to be sparse, and there is a need for additional observations to provide new scientific insight into the geophysical source phenomenology and wave propagation physics. The dense network of GPS receivers around the globe offers a relatively new data source to observe and monitor TIDs. In this paper, we use Total Electron Content (TEC) measurements from ~4000 GPS receivers throughout the continental United States to |
observe TIDs associated with the 11 March 2011 Tohoku tsunami. The tsunami propagated across the Pacific to the US west coast over several hours, and we show that corresponding TIDs were observed in the US. Using this network of GPS receivers we present a 2D imaging of TEC perturbations and calculate various TID parameters, including horizontal wavelength, speed, and period. Well-formed, planar traveling ionospheric disturbances were detected over the west coast of the US ~10 hours after the earthquake. Fast Fourier transform analysis of the observed waveforms revealed that the period of the wave was 15.1 minutes with a horizontal wavelength of 194.8 km, phase velocity of 233.0 m/s, and an azimuth of 105.2° (propagating nearly due east in the direction of the tsunami wave). These results are consistent with the TID observations in airglow measurements from Hawaii earlier in the day [Makela et al., 2011], and with other GPS TEC observations [Tsugawa et al., 2011; Galvan et al., 2012]. |
Mayo de 2016
Active tectonics west of New Zealand's Alpine Fault: South Westland Fault Zone activity shows Australian Plate instability
Authors: Gregory P. De Pascale, Nicholas Chandler-Yates et al
Link: Click here
Abstract
The 300 km long South Westland Fault Zone (SWFZ) is within the footwall of the Central Alpine Fault (<20 km away) and has 3500 m of dip-slip displacement, but it has been unknown if the fault is active. Here the first evidence for SWFZ thrust faulting in the “stable” Australian Plate is shown with cumulative dip-slip displacements up to
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5.9 m (with 3 m throw) on Pleistocene and Holocene sediments and gentle hanging wall anticlinal folding. Cone penetration test (CPT) stratigraphy shows repeated sequences within the fault scarp (consistent with thrusting). Optically stimulated luminescence (OSL) dating constrains the most recent rupture post-12.1 ± 1.7 ka with evidence for three to four events during earthquakes of at least Mw 6.8. This study shows significant deformation is accommodated on poorly characterized Australian Plate structures northwest of the Alpine Fault and demonstrates that major active and seismogenic structures remain uncharacterized in densely forested regions on Earth. |
Mayo de 2016
The mass balance of earthquakes and earthquake sequences
Authors: O. Marc, N. Hovius et al
Link: Click here
Abstract
Large, compressional earthquakes cause surface uplift as well as widespread mass wasting. Knowledge of their trade-off is fragmentary. Combining a seismologically consistent model of earthquake-triggered landsliding and an analytical solution of coseismic surface displacement, we assess how the mass balance of single earthquakes and earthquake sequences depends
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on fault size and other geophysical parameters. We find that intermediate size earthquakes (Mw 6–7.3) may cause more erosion than uplift, controlled primarily by seismic source depth and landscape steepness, and less so by fault dip and rake. Such earthquakes can limit topographic growth, but our model indicates that both smaller and larger earthquakes (Mw < 6, Mw > 7.3) systematically cause mountain building. Earthquake sequences with a Gutenberg-Richter distribution have a greater tendency to lead to predominant erosion, than repeating earthquakes of the same magnitude, unless a fault can produce earthquakes with Mw > 8 or more. |
Mayo de 2016
Extreme temperature and precipitation events in March 2015 in central and northern Chile
Authors: Bradford S. Barrett, Diego A. Campos et al
Link: Click here
Abstract
From 18 to 27 March 2015, northern, central, and southern Chile experienced a series of extreme hydrometeorological events. First, the highest surface air temperature ever recorded in Santiago (with reliable records dating to 1877), 36.8°C at Quinta Normal, was measured at 15:47 local time on 20 March 2015. Immediately following this high heat event, an extreme precipitation event, with damaging streamflows from precipitation totals greater than 45 mm, occurred in the semiarid and hyperarid Atacama regions. Finally, concurrent with the heavy precipitation event, extremely warm temperatures were recorded throughout southern Chile. These events were
|
examined from a synoptic perspective with the goal of identifying forcing mechanisms and potential interaction between each analysis which provides operational context by which to identify and predict similar events in the future. Primary findings were as follows: (1) record warm temperatures in central Chile resulted from anomalous lower troposphere ridging and easterly downslope flow, both of which developed in response to an anomalous midtroposphere ridge-trough pattern; (2) a cutoff low with anomalous heights near one standard deviation below normal slowly moved east and was steered ashore near 25°S by circulation around a very strong ridge (anomalies more than 3 standard deviations above normal) centered near 60°S; (3) anomalously high precipitable water content (20 mm above climatological norms) over the Peruvian Bight region was advected southward and eastward ahead of the cutoff low by low-level northwesterly flow, greatly enhancing observed precipitation over northern Chile. |
Mayo de 2016
New analytic solutions for modeling vertical gravity gradient anomalies
Authors: Seung-Sep Kim and Paul Wessell
Link: Click here
Abstract
Modern processing of satellite altimetry for use in marine gravimetry involves computing the along-track slopes of observed sea-surface heights, projecting them into east-west and north-south deflection of the vertical grids, and using Laplace's equation to algebraically obtain a grid of the vertical gravity gradient (VGG). The VGG grid is then integrated via overlapping, flat Earth Fourier transforms to yield a free-air anomaly grid. Because of this integration and associated edge |
effects, the VGG grid retains more short-wavelength information (e.g., fracture zone and seamount signatures) that is of particular importance for plate tectonic investigations. While modeling of gravity anomalies over arbitrary bodies has long been a standard undertaking, similar modeling of VGG anomalies over oceanic features is not commonplace yet. Here we derive analytic solutions for VGG anomalies over simple bodies and arbitrary 2-D and 3-D sources. We demonstrate their usability in determining mass excess and deficiency across the Mendocino fracture zone (a 2-D feature) and find the best bulk density estimate for Jasper seamount (a 3-D feature). The methodologies used herein are implemented in the Generic Mapping Tools, available from gmt.soest.hawaii.edu. |
Mayo de 2016
Joint modeling of teleseismic and tsunami wave observations to constrain the 16 September 2015 Illapel, Chile, Mw 8.3 earthquake rupture process
Authors: Linyan Li, Thorne Lay et al
Link: Click here
Abstract
The 16 September 2015 Illapel, Chile, Mw 8.3 earthquake ruptured ~170 km along the plate boundary megathrust fault from 30.0°S to 31.6°S. A patch of offshore slip of up to 10 m extended to near the trench, and a patch of ~3 m slip occurred downdip below the coast. Aftershocks fringe the large-slip zone, extending along the |
coast from 29.5°S to 32.5°S between the 1922 and 1971/1985 ruptures. The coseismic slip distribution is determined by iterative modeling of teleseismic body waves as well as tsunami signals recorded at three regional DART stations and tide gauges immediately north and south of the rupture. The tsunami observations tightly delimit the rupture length, suppressing bilateral southward extension of slip found in unconstrained teleseismic-wave inversions. The spatially concentrated rupture area, with a stress drop of ~3.2 MPa, is validated by modeling DART and tide gauge observations in Hawaii, which also prove sensitive to the along-strike length of the rupture. |
Mayo de 2016
Two-stage composite megathrust rupture of the 2015 Mw8.4 Illapel, Chile earthquake identified by spectral-element inversion of teleseismic waves
Authors: Shiann-Jong Lee, Te-Yang Yeh et al
Link: Click here
Abstract
The Mw8.4 Illapel earthquake occurred on 16th September was the largest global event in 2015. This earthquake was not unexpected because the hypocenter was located in a seismic gap of the Peru–Chile subduction zone. However, the source model derived from 3D spectral-element inversion
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of teleseismic waves reveals a distinct two-stage rupture process with completely different slip characteristics as a composite megathrust event. The two stages were temporally separated. Rupture in the first stage, with a moment magnitude of Mw8.32, built up energetically from the deeper locked zone and propagated in the up-dip direction toward the trench. Subsequently, the rupture of the second stage, with a magnitude of Mw8.08, mainly occurred in the shallow subduction zone with atypical repeating slip behavior. The unique spatial-temporal rupture evolution presented in this source model is key to further in-depth studies of earthquake physics and source dynamics in subduction systems. |
Abril de 2016
A multivariate Copula-based framework for dealing with Hazard Scenarios and Failure Probabilities
Authors: G. Salvadori, F. Durante et al
Link: Click here
Abstract
This paper is of methodological nature, and deals with the foundations of Risk Assessment. Several international guidelines have recently recommended to select appropriate/relevant Hazard Scenarios in order to tame the consequences of (extreme) natural phenomena. In particular, the scenarios should be multivariate, i.e. they should take into account the fact that several variables, generally not independent, may be of interest. In this work, it is shown how a Hazard Scenario can be identified in terms of (i) a specific geometry and (ii) a suitable probability level. Several scenarios, as well as a Structural approach, are presented, and due comparisons
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the Copula Theory, which turns out to be a fundamental theoretical apparatus for doing multivariate risk assessment: formulas for the calculation of the probability of Hazard Scenarios in the general multi-dimensional case (d ≥ 2) are derived, and worthy analytical relationships among the probabilities of occurrence of Hazard Scenarios are presented. In addition, the Extreme Value and Archimedean special cases are dealt with, relationships between dependence ordering and scenario levels are studied, and a counter-example concerning Tail Dependence is shown. Suitable indications for the practical application of the techniques outlined in the work are given, and two case studies illustrate the procedures discussed in the paper. This article is protected by copyright. All rights reserved. are carried out. In addition, it is shown how the Hazard Scenario approach illustrated here is well suited to cope with the notion of Failure Probability, a tool traditionally used for design and risk assessment in engineering practice. All the results outlined throughout the work are based on |
Abril de 2016
Geomechanical analysis of fluid injection and seismic fault slip for the Mw4.8 Timpson, Texas, earthquake sequence
Authors: Zhiqiang Fan, Peter Eichhubl et al
Link: Click here
Abstract
An earthquake sequence that culminated in a Mw4.8 strike-slip event near Timpson, east Texas, the largest reported earthquake to date in that region, had previously been attributed to wastewater injection starting 17 months before the onset of recorded seismic activity. To test if this earthquake sequence can be attributed to wastewater injection, we conducted coupled poroelastic finite element simulations to assess the spatial and temporal evolution of pore pressure and stress field in the vicinity of the
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injection wells and to calculate the Coulomb failure stress on the seismogenic fault as a function of the permeability of the injection layer, fault orientation, fault permeability, and orientation and magnitude of the in situ stress. We find that injection-induced fault slip is plausible within the range of selected model input parameters, with slip favored by low reservoir permeability, low fault permeability, and a favorable orientation of the fault relative to the in situ stress state. Other combinations of equally plausible input parameters predict no slip within 96 months of simulated injection. Under most favorable boundary conditions for fault slip, fault slip occurs 7 months after the start of injection. Our results highlight the importance of detailed geomechanical site characterization for robust fault stability assessment prior to wastewater injection. |
Abril de 2016
Postseismic gravity change after the 2006–2007 great earthquake doublet and constraints on the asthenosphere structure in the central Kuril Islands
Authors: Shin-Chan Han, Jeanne Sauber et al
Link: Click here
Abstract
Large earthquakes often trigger viscoelastic adjustment for years to decades depending on the rheological properties and the nature and spatial extent of coseismic stress. The 2006 Mw8.3 thrust and 2007 Mw8.1 normal fault earthquakes of the central Kuril Islands resulted in significant postseismic gravity change in Gravity Recovery |
and Climate Experiment (GRACE) but without a discernible coseismic gravity change. The gravity increase of ~4 μGal, observed consistently from various GRACE solutions around the epicentral area during 2007–2015, is interpreted as resulting from gradual seafloor uplift by ~6 cm produced by postseismic relaxation. The GRACE data are best fit with a model of 25–35 km for the elastic thickness and ~1018 Pa s for the Maxwell viscosity of the asthenosphere. The large measurable postseismic gravity change (greater than coseismic change) emphasizes the importance of viscoelastic relaxation in understanding tectonic deformation and fault-locking scenarios in the Kuril subduction zone. |
Abril de 2016
Ionosonde tracking of infrasound wavefronts in the thermosphere launched by seismic waves after the 2010 M8.8 Chile earthquake
Authors: Takashi Maruyama, Kamil Yusupov,
et al
Link: Click here
Abstract
Ionospheric disturbances associated with the M8.8 Chile earthquake (35.91°S, 72.73°W) on 27 February 2010 were observed at Kazan, Russia (55.85°N, 48.81°E). Rapid-run ionograms at 1 min intervals exhibited multiple-cusp signatures (MCSs) for more than 30 min, which have been observed several times after large earthquakes. The ionospheric disturbances were caused by infrasound propagating upward in the atmosphere, which modified the electron density
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distribution through ion-neutral collisions. The anomaly of the vertical electron density distribution responsible for the MCSs was analyzed by converting the ionogram traces into real height profiles. The density profiles at 1 min intervals allowed the tracking of the vertical propagation of infrasound and provided information on parameters of acoustic waves, which was not possible from the previous measurements such as standard ionograms at 5–15 min intervals, HF Doppler soundings, and total electron content using satellite beacon signals. The speed of acoustic waves in the thermosphere was evaluated from the consecutive ionograms with MCSs, and it was found that the thermospheric temperature was slightly higher than that calculated using the Mass Spectrometer and Incoherent Scatter Radar empirical model (NRLMSISE-00). |
Abril de 2016
M ≥ 7 earthquake rupture forecast and time-dependent probability for the sea of Marmara region, Turkey
Authors: M. Murru, A. Akinci et al
Link: Click here
Abstract
We forecast time-independent and time-dependent earthquake ruptures in the Marmara region of Turkey for the next 30 years using a new fault segmentation model. We also augment time-dependent Brownian passage time (BPT) probability with static Coulomb stress changes (ΔCFF) from interacting faults. We calculate Mw > 6.5 probability from 26 individual fault sources in the Marmara region. We also consider a multisegment rupture model that allows higher-magnitude ruptures over some segments of the northern branch of the North Anatolian Fault Zone beneath the Marmara Sea. A total of 10 different Mw = 7.0 to Mw = 8.0 multisegment ruptures
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are combined with the other regional faults at rates that balance the overall moment accumulation. We use Gaussian random distributions to treat parameter uncertainties (e.g., aperiodicity, maximum expected magnitude, slip rate, and consequently mean recurrence time) of the statistical distributions associated with each fault source. We then estimate uncertainties of the 30 year probability values for the next characteristic event obtained from three different models (Poisson, BPT, and BPT + ΔCFF) using a Monte Carlo procedure. The Gerede fault segment located at the eastern end of the Marmara region shows the highest 30 year probability, with a Poisson value of 29% and a time-dependent interaction probability of 48%. We find an aggregated 30 year Poisson probability of M > 7.3 earthquakes at Istanbul of 35%, which increases to 47% if time dependence and stress transfer are considered. We calculate a twofold probability gain (ratio time dependent to time independent) on the southern strands of the North Anatolian Fault Zone. |
Abril de 2016
Joint modeling of teleseismic and tsunami wave observations to constrain the 16 September 2015 Illapel, Chile Mw 8.3 earthquake rupture process
Authors: Linyan Li, Thorne Lay et al
Link: Click here
Abstract
The 16 September 2015 Illapel, Chile MW 8.3 earthquake ruptured ~170 km along the plate-boundary megathrust fault from 30.0°S to 31.6°S. A patch of offshore slip of up to 10 m extended to near the trench and a patch of ~3 m slip occurred down-dip below the coast. Aftershocks fringe the large-slip zone, extending along the coast from
|
29.5°S to 32.5°S between the 1922 and 1971/1985 ruptures. The coseismic slip distribution is determined by iterative modeling of teleseismic body waves and tsunami signals recorded at three regional DART stations and tide-gauges immediately north and south of the rupture. The tsunami observations tightly delimit the rupture length, suppressing bilateral southward extension of slip found in unconstrained teleseismic-wave inversions. The spatially concentrated rupture area, with a stress drop of ~3.2 MPa, is validated by modeling DART and tide-gauge observations in Hawaii, which also prove sensitive to the along-strike length of the rupture. |
Abril de 2016
Collective Properties of Injection-Induced Earthquake Sequences Part 1: Model Description and Directivity Bias
Authors: David Dempsey and Jenny Suckale
Link: Click here
Abstract
Induced seismicity is of increasing concern for oil and gas, geothermal and carbon sequestration operations, with several M>5 events triggered in recent years. Modeling plays an important role in understanding the causes of this seismicity and in constraining seismic hazard. Here, we study the collective properties of induced earthquake sequences and the physics underpinning them. In this first paper of a two-part series, we focus on the directivity ratio, which quantifies whether fault rupture is dominated by one (unilateral) or two (bilateral) propagating fronts. In a second paper, we focus on the spatiotemporal and magnitude-frequency distributions of induced seismicity. We develop a model that couples a fracture mechanics description of 1D fault rupture with fractal stress heterogeneity and the evolving pore |
pressure distribution around an injection well that triggers earthquakes. The extent of fault rupture is calculated from the equations of motion for two tips of an expanding crack centered at the
earthquake hypocenter. Under tectonic loading conditions, our model exhibits a preference for unilateral rupture and a normal distribution of hypocenter locations, two features that are consistent with seismological observations. On the other hand, catalogs of induced events when injection occurs directly onto a fault exhibit a bias toward ruptures that propagate toward the injection well. This bias is due to relatively favorable conditions for rupture that exist within the high pressure plume. The strength of the directivity bias depends on a number of factors including the style of pressure build-up, the proximity of the fault to failure, and event magnitude. For injection off a fault that triggers earthquakes, the modeled directivity bias is small and may be too weak for practical detection. For two hypothetical injection scenarios, we estimate the number of earthquake observations required to detect directivity bias. |
Abril de 2016
A seismologically consistent expression for the total area and volume of earthquake-triggered landsliding
Authors: H. Yanagisawa, K. Goto et al
Link: Click here
Abstract
Since the March 11, 2011 Tohoku earthquake, the mechanisms of large earthquakes along the Japan Trench have been intensely investigated. However, characteristics of tsunami earthquakes, which trigger unusually large tsunami, remain unknown. The earthquake of November 4, 1677 was a tsunami earthquake striking the southern part of the Japan Trench. Its source mechanism remains unclear. This study elucidates the fault slip and moment magnitude of the 1677 earthquake and tsunami based on integrated analyses of historical documents, tsunami deposits, and numerical simulation. Geological survey results, the analytical results of thickness
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and grain size distributions and diatoms, revealed that tsunami deposits in a small pond at 11 m elevation were probably formed by the 1677 event. This finding and historical descriptions are useful as important constraint conditions to estimate unusually large fault slips and moment magnitude of the 1677 earthquake. Numerical simulation results reveal that 8.34–8.63 moment magnitude with the large 11–16 m slip area is necessary to satisfy the constraint conditions. This fault slip and magnitude are equivalent to those of the 1896 Sanriku earthquake: a well-known tsunami earthquake in the northern part of the Japan Trench. We therefore conclude that a tsunami earthquake of moment magnitude 8.3–8.6 with unusually large slip can occur elsewhere along the Japan Trench. This point should be considered for future tsunami risk assessment along the Japan Trench and along any trench having similar tectonic settings to those of the Japan Trench. |
Abril de 2016
A seismologically consistent expression for the total area and volume of earthquake-triggered landsliding
Authors: Odin Marc, Niels Hovius et al
Link: Click here
Abstract
We present a new, seismologically consistent expression for the total area and volume of populations of earthquake-triggered landslides. This model builds on a set of scaling relationships between key parameters, such as landslide spatial density, seismic ground acceleration, fault length, earthquake source depth, and seismic moment. To assess the model we have assembled and normalized a catalog of landslide inventories for 40 shallow, continental earthquakes. Low landscape steepness causes systematic overprediction of the total area and volume of landslides. When this
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effect is accounted for, the model predicts the total landslide volume of 63% of 40 cases to within a factor 2 of the volume estimated from observations (R2=0.76). The prediction of total landslide area is also sensitive to the landscape steepness, but less so than the total volume, and it appears to be sensitive to controls on the landslide size-frequency distribution, and possibly the shaking duration. Some outliers are likely associated with exceptionally strong rock mass in the epicentral area, while others may be related to seismic source complexities ignored by the model. However, the close match between prediction and estimate for about two thirds of cases in our database suggests that rock mass strength is similar in many cases and that our simple seismic model is often adequate, despite the variety of lithologies and tectonic settings covered. This makes our expression suitable for integration into landscape evolution models and application to the anticipation or rapid assessment of secondary hazards associated with earthquakes. |
Abril de 2016
Injection-induced seismicity on basement faults including poroelastic stressing
Authors: K. W. Chang and P. Segall
Link: Click here
Abstract
Most significant induced earthquakes occur on faults within the basement beneath sedimentary cover. In this two-dimensional plane strain numerical study, we examine the full poroelastic response of basement faults to fluid injection into overlying strata, considering both (1) the permeability of the fault zone and (2) the hydraulic connectivity of the faults to the target horizon. Given hydraulic and mechanical properties, we compute the spatiotemporal change in Coulomb stress, which we separate into (1) the change in
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poroelastic stresses Δτs+fΔσn, where Δτs and Δσn are changes in shear and normal stress (Δτs>0 and Δσn>0 both favor slip), and (2) the change in pore pressure fΔp. Pore pressure diffusion into hydraulically connected, permeable faults dominates their mechanical stability. For hydraulically isolated or low-permeability faults, however, poroelastic stresses transmitted to deeper basement levels can trigger slip, even without elevated pore pressure. The seismicity rate on basement fault zones is predicted using the model of Dieterich (1994). High seismicity rates can occur on permeable, hydraulically connected faults due to direct pore pressure diffusion. Lower rates are predicted on isolated steeply dipping normal faults, caused solely by poroelastic stressing. In contrast, seismicity on similarly oriented reverse faults is inhibited. |
Abril de 2016
Extreme temperature and precipitation events in March 2015 in central and northern Chile
Authors: Bradford S. Barrett, Diego A. Campos et al
Link: Click here
Abstract
From 18-27 March 2015, northern, central, and southern Chile experienced a series of extreme hydrometeorological events. First, the highest surface air temperature ever recorded in Santiago (with reliable records dating to 1877), 36.8 °C at Quinta Normal, was measured at 15:47 local time on 20 March 2015. Immediately following this high heat event, an extreme precipitation event, with damaging streamflows from precipitation totals greater than 45 mm, occurred in the semi- and hyper-arid Atacama regions. Finally, concurrent with the heavy precipitation event, extremely warm temperatures were recorded throughout southern Chile. These events were examined from a
|
synoptic perspective with the goal of identifying forcing mechanisms and potential interaction between each, analysis which provides operational context by which to identify and predict similar events in the future.
Primary findings were as follows: (1) record warm temperatures in central Chile resulted from anomalous lower-troposphere ridging and easterly downslope flow, both of which developed in response to an anomalous mid-troposphere ridge-trough pattern; (2) a cutoff low with anomalous heights near one standard deviation below normal slowly moved east and was steered ashore near 25°S by circulation around a very strong ridge (anomalies more than 3 standard deviations above normal) centered near 60°S; (3) anomalously high precipitable water content (20 mm above climatological norms) over the Peruvian Bight region was advected southward and eastward ahead of the cutoff low by low-level northwesterly flow, greatly enhancing observed precipitation over northern Chile. |
Abril de 2016
Geomechanical analysis of fluid injection and seismic fault slip for the M4.8 Timpson, Texas, earthquake sequence
Authors: Zhiqiang Fan, Peter Eichhubl et al
Link: Click here
Abstract
An earthquake sequence that culminated in a MW4.8 strike-slip event near Timpson, east Texas, the largest reported earthquake to date in that region, had previously been attributed to wastewater injection starting 17 months before the onset of recorded seismic activity. To test if this earthquake sequence can be attributed to wastewater injection, we conducted coupled poroelastic finite element simulations to assess the spatial and temporal evolution of pore pressure and stress field in the vicinity of the
|
injection wells and to calculate the Coulomb failure stress on the seismogenic fault as a function of the permeability of the injection layer, fault orientation, fault permeability, and orientation and magnitude of the in situ stress. We find that injection-induced fault slip is plausible within the range of selected model input parameters, with slip favored by low reservoir permeability, low fault permeability, and a favorable orientation of the fault relative to the in situ stress state. Other combinations of equally plausible input parameters predict no slip within 96 months of simulated injection. Under most favorable boundary conditions for fault slip, fault slip occurs 7 months after the start of injection. Our results highlight the importance of detailed geomechanical site characterization for robust fault stability assessment prior to wastewater injection. |
Abril de 2016
Using a genetic algorithm to estimate the details of earthquake slip distributions from point surface displacements
Authors: A. Lindsay, J. McCloskey et al
Link: Click here
Abstract
Examining fault activity over several earthquake cycles is necessary for long-term modeling of the fault strain budget and stress state. While this requires knowledge of coseismic slip distributions for successive earthquakes along the fault, these exist only for the most recent events. However, overlying the Sunda Trench, sparsely distributed coral microatolls are sensitive to tectonically induced changes in relative sea levels and provide a century-spanning paleogeodetic and paleoseismic record. Here we present a new technique called the Genetic Algorithm Slip Estimator to constrain slip distributions from observed surface deformations of corals. We identify a suite of models consistent
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with the observations, and from them we compute an ensemble estimate of the causative slip. We systematically test our technique using synthetic data. Applying the technique to observed coral displacements for the 2005 Nias-Simeulue earthquake and 2007 Mentawai sequence, we reproduce key features of slip present in previously published inversions such as the magnitude and location of slip asperities. From the displacement data available for the 1797 and 1833 Mentawai earthquakes, we present slip estimates reproducing observed displacements. The areas of highest modeled slip in the paleoearthquake are nonoverlapping, and our solutions appear to tile the plate interface, complementing one another. This observation is supported by the complex rupture pattern of the 2007 Mentawai sequence, underlining the need to examine earthquake occurrence through long-term strain budget and stress modeling. Although developed to estimate earthquake slip, the technique is readily adaptable for a wider range of applications. |
Abril de 2016
Systematic assessment of the static stress triggering hypothesis using interearthquake time statistics
Authors: Shyam Nandan, Guy Ouillon et al
Link: Click here
Abstract
A likely source of earthquake clustering is static stress transfer between individual events. Previous attempts to quantify the role of static stress for earthquake triggering generally considered only the stress changes caused by large events and often discarded data uncertainties. We conducted a robust twofold empirical test of the static stress change hypothesis by accounting for all events of magnitude M ≥ 2.5 and their location and focal mechanism uncertainties provided by catalogs for Southern California between 1981 and 2010, first after resolving the focal plane ambiguity and second after randomly choosing one of the two
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nodal planes. For both cases, we find compelling evidence supporting the static triggering with stronger evidence after resolving the focal plane ambiguity above significantly small (about 10 Pa) but consistently observed stress thresholds. The evidence for the static triggering hypothesis is robust with respect to the choice of the friction coefficient, Skempton's coefficient, and magnitude threshold. Weak correlations between the Coulomb index (fraction of earthquakes that received positive Coulomb stress change) and the coefficient of friction indicate that the role of normal stress in triggering is rather limited. Last but not the least, we determined that the characteristic time for the loss of the stress change memory of a single event is nearly independent of the amplitude of the Coulomb stress change and varies between ~95 and ~180 days implying that forecasts based on static stress changes will have poor predictive skills beyond times that are larger than a few hundred days on average. |
Abril de 2016
Seismic azimuthal anisotropy in the oceanic lithosphere and asthenosphere from broadband surface wave analysis of OBS array records at 60 Ma seafloor
Authors: A. Takeo, H. Kawakatsu et al
Link: Click here
Abstract
We analyzed seismic ambient noise and teleseismic waveforms of nine broadband ocean bottom seismometers deployed at a 60 Ma seafloor in the southeastward of Tahiti island, the South Pacific, by the Tomographic Investigation by seafloor ARray Experiment for the Society hotspot project. We first obtained one-dimensional shear wave velocity model beneath the array from average phase velocities of Rayleigh waves at a broadband period range of 5–200 s. The obtained model shows a large velocity reduction at depths |
between 40 and 80 km, where the lithosphere-asthenosphere boundary might exist. We then estimated shear wave azimuthal anisotropy at depths of 20–100 km by measuring azimuthal dependence of phase velocities of Rayleigh waves. The obtained model shows peak-to-peak intensity of the azimuthal anisotropy of 2%–4% with the fastest azimuth of NW–SE direction both in the lithosphere and asthenosphere. This result suggests that the ancient flow frozen in the lithosphere is not perpendicular to the strike of the ancient mid-ocean ridge but is roughly parallel to the ancient plate motion at depths of 20–60 km. The fastest azimuths in the current asthenosphere are subparallel to current plate motion at depths of 60–100 km. Additional shear wave splitting analysis revealed possible perturbations of flow in the mantle by the hot spot activities and implied the presence of azimuthal anisotropy in the asthenosphere down to a depth of 190–210 km. |
Abril de 2016
Lithospheric flexure and gravity spreading of Olympus Mons volcano, Mars
Authors: S. Musiol, E. P. Holohan et al
Link: Click here
Abstract
The structural architecture of large volcanoes is governed substantially by gravity-driven deformation that is manifest as distinct processes such as basement flexure or volcanic spreading. Temporal effects and the mutual interplay of these processes have been investigated only to a limited extent, and so we present novel numerical models of the time-dependent deformation associated with them. The models simulate the combined effects of lithospheric flexure and volcanic spreading during growth increments of an elastoplastic volcanic cone. Different spreading scenarios are considered by a variable coupling |
decoupling behavior at the interface between volcano and basement. We apply our models to Olympus Mons on Mars, which is characterized by upper to middle flank terraces on the shield, is encircled by a basal scarp that has an average slope of 30° and is surrounded by distant deposits that resemble large-scale slumping features on Earth. Our results are consistent with the interpretation that terraces on Olympus Mons' flanks form by thrust faulting that results from lithospheric flexure. The presence and expression of terraces depend on the coupling of volcano and basement, on the time of volcano growth relative to mantle relaxation, and on the cohesion of the edifice. The encircling scarp may be related to a very low friction detachment at the edifice base, which leads to a normal fault regime on the lowermost flanks. With time and volcano growth, predicted stress and faulting regimes migrate only slightly, indicating that the structural architecture of volcanoes is largely set in the very early stages of formation. |
Abril de 2016
Volcanic lightning and plume behavior reveal evolving hazards during the April 2015 eruption of Calbuco volcano, Chile
Authors: Alexa R. Van Eaton, Álvaro Amigo et al
Link: Click here
Abstract
Soon after the onset of an eruption, model forecasts of ash dispersal are used to mitigate the hazards to aircraft, infrastructure, and communities downwind. However, it is a significant challenge to constrain the model inputs during an evolving eruption. Here we demonstrate that volcanic lightning may be used in tandem with |
satellite detection to recognize and quantify changes in eruption style and intensity. Using the eruption of Calbuco volcano in southern Chile on 22 and 23 April 2015, we investigate rates of umbrella cloud expansion from satellite observations, occurrence of lightning, and mapped characteristics of the fall deposits. Our remote sensing analysis gives a total erupted volume that is within uncertainty of the mapped volume (0.56 ± 0.28 km3 bulk). Observations and volcanic plume modeling further suggest that electrical activity was enhanced both by ice formation in the ash clouds >10 km above sea level and development of a low-level charge layer from ground-hugging currents. |
Abril de 2016
Nature of the seismic lithosphere-asthenosphere boundary within normal oceanic mantle from high-resolution receiver functions
Authors: Tolulope Morayo Olugboji, Jeffrey Park et al
Link: Click here
Abstract
Receiver function observations in the oceanic upper mantle can test causal mechanisms for the depth, sharpness, and age dependence of the seismic wave speed decrease thought to mark the lithosphere-asthenosphere boundary (LAB). We use a combination of frequency-dependent harmonic decomposition of receiver functions and synthetic forward modeling to provide new seismological constraints on this “seismic LAB” from 17 ocean-bottom stations and 2 borehole stations in the Philippine Sea and northwest Pacific Ocean. Underneath young oceanic crust, the seismic LAB depth follows the ∼1300 K isotherm but a lower isotherm (∼1000 K) is suggested in the Daito ridge, the Izu-Bonin-Mariana trench, and the northern Shikoku basin. Underneath old oceanic crust, the seismic LAB
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lies at a constant depth ∼70 km. The age dependence of the seismic LAB depth is consistent with either a transition to partial-melt conditions or a subsolidus rheological change as the causative factor. The age dependence of interface sharpness provides critical information to distinguish these two models. Underneath young oceanic crust, the velocity gradient is gradational, while for old oceanic crust, a sharper velocity gradient is suggested by the receiver functions. This behavior is consistent with the prediction of the subsolidus model invoking anelastic relaxation mediated by temperature and water content, but is not readily explained by a partial-melt model. The Ps conversions display negligible two-lobed or four-lobed back azimuth dependence in harmonic stacks, suggesting that a sharp change in azimuthal anisotropy with depth is not responsible for them. We conclude that these ocean-bottom observations indicate a subsolidus elastically accommodated grain-boundary sliding (EAGBS) model for the seismic LAB. Because EAGBS does not facilitate long-term ductile deformation, the seismic LAB may not coincide with the conventional transition from lithosphere to asthenosphere corresponding to a change in the long-term rheological properties. |
Abril de 2016
The mass balance of earthquakes and earthquake sequences
Authors: O. Marc, N. Hovius et al
Link: Click here
Abstract
Large, compressional earthquakes cause surface uplift as well as widespread mass wasting. Knowledge of their trade-off is fragmentary. Combining a seismologically-consistent model of earthquake-triggered landsliding and an analytical solution of coseismic surface displacement, we assess how the mass balance of single earthquakes and earthquake sequences depends
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on fault size and other geophysical parameters. We find that intermediate size earthquakes (Mw6.-7.3) may cause more erosion than uplift, controlled primarily by seismic source depth and landscape steepness, and less so by fault dip and rake. Such earthquakes can limit topographic growth, but our model indicates that both smaller and larger earthquakes (Mw < 6, Mw > 7.3) systematically cause mountain building. Earthquake sequences with a Gutenberg-Richter distribution have a greater tendency to lead to predominant erosion, than repeating earthquakes of the same magnitude, unless a fault can produce earthquakes with Mw > 8 or more. |
Abril de 2016
Application of Array Back-projection to Tsunami Prediction and Early Warning
Authors: Chao An and Lingsen Meng
Link: Click here
Abstract
Teleseismic and static geodetic data have weak constraints on the off-shore slip while tsunami data are limited by their availability, so predictions of tsunami waves in the near-field remain challenging. In this study, we develop a near-field tsunami prediction approach based on seismic array back-projections (BP). In this approach, the
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rupture area is first estimated by enclosing the BP radiators. Then slip models with uniform slip are constructed based on statistical scaling relations between rupture area and seismic moment to predict the near-field tsunami waveforms. The method is applied to the 2011 Tohoku, 2014 Iquique and 2015 Illapel tsunami events, and the model predictions are compared with tsunami recordings at 57 tidal gauges and 9 DART stations. Results shows that the average error of arrival time and amplitude near-shore is approximately −15 ∼+ 5 min and 0.5 m, respectively, which are sufficiently small for tsunami warning purposes. |
Marzo de 2016
Aeromagnetic investigation of southern Calabria and the Messina Straits (Italy): Tracking seismogenic sources of 1783 and 1908 earthquakes
Authors: Liliana Minelli, Antonio Vecchio et al
Link: Click here
Abstract
Southern Calabria and the NE corner of Sicily (Italy) were struck in 1783 and 1908 A.D. by two of the most catastrophic earthquakes ever in European history. Although it is generally acknowledged that the seisms were yielded by normal faults rupturing the upper crust of the Calabria-Peloritani terrane, no consensus exists on seismogenic source location and orientation. Here we report on a high-resolution low-altitude aeromagnetic survey of southern Calabria and Messina Straits. In southern Calabria we document a broad weakly positive (5–10 nT) anomaly zone interrupted by three en echelon SW- |
NE null to negative magnetic anomaly corridors. Euler deconvolution and magnetic modeling show that the anomaly pattern is produced by a 1–1.5 km thick crustal “layer” located within 3 km depth. This layer is offset by a 25 km long NE trending fault that corresponds to the Armo normal fault, recently inferred to be the source for the 1908 earthquake. Few kilometers to the south, we also document a subparallel and previously unrecognized fault, entering the Messina Straits and likely joining the Armo fault at depth. Further east, we model a 40 km long normal fault, probably extending northeastward for additional 40 km, running along the south Calabria axis from Aspromonte to the Serre mountains and partly following the 18 km long surface rupture witnessed by Déodat de Dolomieu after the 1783 earthquake. Thus, aeromagnetic data suggest that the sources of the 1783 and 1908 earthquakes are en echelon faults belonging to the same NW dipping normal fault system straddling the whole southern Calabria. |
Marzo de 2016
Comparing source inversion techniques for GPS-based local tsunami forecasting: a case study for the April 2014 M8.1 Iquique, Chile earthquake
Authors: Kejie Chen, Andrey Babeyko et al
Link: Click here
Abstract
Real-time GPS is nowadays considered as a valuable component of next generation near-field tsunami early warning systems able to provide fast and reliable source parameters. Looking for optimal methodologies and assessing corresponding uncertainties becomes an important task. We take the opportunity and
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consider the 2014 Pisagua event as a case study to explore tsunami forecast uncertainty related to the GPS-based source inversion. We intentionally neglect all other sources of uncertainty (observation set, signal processing, wave simulation, etc.) and exclusively assess the effect of inversion technique. In particular, we compare three end-member methods: (1) point-source fastCMT (centroid moment tensor) (2) distributed slip along pre-defined plate interface and (3) unconstrained inversion into a single uniform-slip finite fault. The three methods provide significantly different far-field tsunami forecast but show surprisingly similar tsunami predictions in the near-field. |
Marzo de 2016
Exploring the relationship between the magnitudes of seismic events
Authors: Ilaria Spassiani, Giovanni Sebastiani et al
Link: Click here
Abstract
The distribution of the magnitudes of seismic events is generally assumed to be independent on past seismicity. However, by considering events in causal relation, for example, mother-daughter, it seems natural to assume that the magnitude of a daughter event is conditionally dependent on one of the corresponding mother
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events. In order to find experimental evidence supporting this hypothesis, we analyze different catalogs, both real and simulated, in two different ways. From each catalog, we obtain the law of the magnitude of the triggered events by kernel density. The results obtained show that the distribution density of the magnitude of the triggered events varies with the magnitude of their corresponding mother events. As the intuition suggests, an increase of the magnitude of the mother events induces an increase of the probability of having “high” values of the magnitude of the triggered events. In addition, we see a statistically significant increasing linear dependence of the magnitude means. |
Marzo de 2016
Three-dimensional displacement field of the 2015 Mw8.3 Illapel earthquake (Chile) from across- and along-track Sentinel-1 TOPS interferometry
Authors: R. Grandin, E. Klein et al
Link: Click here
Abstract
Wide-swath imaging has become a standard acquisition mode for radar missions aiming at applying synthetic aperture radar interferometry (InSAR) at global scale with enhanced revisit frequency. Increased swath width, compared to classical Stripmap imaging mode, is achieved at the expense of azimuthal resolution. This makes along-track displacements, and subsequently
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north-south displacements, difficult to measure using conventional split-beam (multiple-aperture) InSAR or cross-correlation techniques. Alternatively, we show here that the along-track component of ground motion can be deduced from the double difference between backward and forward looking interferograms within regions of burst overlap. “Burst overlap interferometry” takes advantage of the large squint angle diversity of Sentinel-1 (1°) to achieve subdecimetric accuracy on the along-track component of ground motion. We demonstrate the efficiency of this method using Sentinel-1 data covering the 2015 Mw8.3 Illapel earthquake (Chile) for which we retrieve the full 3-D displacement field and validate it against observations from a dense network of GPS sensors. |
Marzo de 2016
Coseismic radiation and stress drop during the 2015 Mw 8.3 Illapel, Chile megathrust earthquake
Authors: Jiuxun Yin, Hongfeng Yang et al
Link: Click here
Abstract
On 16 September 2015, an Mw 8.3 earthquake struck middle Chile due to the subduction of the Nazca plate beneath the South America plate. This earthquake is the consequence of 72 years of strain accumulation in the region since the 1943 M 8.3 event. In this study, we apply the compressive sensing method (CS) to invert for the spatiotemporal distribution of the coseismic radiation at different frequencies of this event. The results show clear frequency-dependent feature of earthquake rupture with low-frequency (LF) radiation located in the updip region while high-frequency (HF) radiation concentrated in the |
downdip region of the megathrust. We also compare the CS results with three coseismic slip models as well as the stress drop distributions inferred from these slip models. The comparison confirms our understanding of coseismic radiation that energy sources are mostly located in the margin of large coseismic slip regions. Furthermore, we find that the LF radiation sources are mainly within the stress-decreasing (releasing) regions while the HF radiation sources are mainly located in the stress-increasing (loading) regions due to rupturing of relatively large asperities nearby (stress decreasing and releasing). These results help to better understand the physics of the rupture process during megathrust earthquakes. Moreover, our results do not show radiation sources south of the epicenter, suggesting that the subducting Juan Fernandez Ridge probably stopped the rupture of this earthquake toward the south. |
Marzo de 2016
Ionosonde tracking of infrasound wavefronts in the thermosphere launched by seismic waves after the 2010 M8.8 Chile earthquake
Authors: Takashi Maruyama, Kamil Yusupov et al
Link: Click here
Abstract
Ionospheric disturbances associated with the M8.8 Chile earthquake (35.91°S, 72.73°W) on 27 February 2010 were observed at Kazan, Russia (55.85°N, 48.81°E). Rapid-run ionograms at 1 min intervals exhibited multiple-cusp signatures (MCSs) for more than 30 min, which have been observed several times after large earthquakes. The ionospheric disturbances were caused by infrasound propagating upward in the atmosphere, which modified the electron density distribution through ion-neutral collisions. The |
anomaly of the vertical electron density distribution responsible for the MCSs was analyzed by converting the ionogram traces into real height profiles. The density profiles at 1 min intervals allowed the tracking of the vertical propagation of infrasound and provided information on parameters of acoustic waves, which was not possible from the previous measurements such as standard ionograms at 5–15 min intervals, HF Doppler soundings, and total electron content using satellite beacon signals. The speed of acoustic waves in the thermosphere was evaluated from the consecutive ionograms with MCSs, and it was found that the thermospheric temperature was slightly higher than that calculated using the Mass Spectrometer and Incoherent Scatter Radar empirical model (NRLMSISE-00). |
Marzo de 2016
Near- and far-field tsunamigenic effects on the Z component of the geomagnetic field during the Japanese event, 2011
Authors: Virginia Klausner, Esfhan A. Kherani et al
Link: Click here
Abstract
In this work, we examine the vertical component (Z) of the geomagnetic field observed by ground-based observatories during the tsunami event which happened on 11 March 2011. For this event, we have selected nine magnetic observatories distributed along the tsunami passage, covering up to 3000 km epicentral distance. The traveltime |
diagram of the magnetic disturbances is constructed and compared with the simulated tsunami traveltime diagram. From this comparison, we identify the amplified magnetic disturbances appearing during the tsunami arrival in the vicinity of these observatories. Moreover, mean absolute percentage error map is constructed to examine the cross correlations among different observatories and the amplified disturbances are found to be highly correlated. These features suggest that the amplified disturbances are tsunamigenic in nature. These results are in confirmation with the previous near-field studies, and they shed new insight into the tsunamigenic magnetic disturbances on near- and far-field distances from the epicenter. |
Marzo de 2016
The vertical propagation of disturbances triggered by seismic waves of the 11 March 2011 M9.0 Tohoku earthquake over Taiwan
Authors: J. Y. Liu, C. H. Chen et al
Link: Click here
Abstract
In this paper, concurrent/colocated measurements of seismometers, infrasonic systems, magnetometers, HF-CW (high frequency-continuous wave) Doppler sounding systems, and GPS receivers are employed to detect disturbances triggered by seismic waves of the 11 March 2011 M9.0 Tohoku earthquake. No time delay between colocated infrasonic (i.e., super long acoustic) waves and seismic waves indicates that the triggered acoustic and/or gravity |
waves in the atmosphere (or seismo-traveling atmospheric disturbances, STADs) near the Earth's surface can be immediately activated by vertical ground motions. The circle method is used to find the origin and compute the observed horizontal traveling speed of the triggered infrasonic waves. The speed of about 3.3 km/s computed from the arrival time versus the epicentral distance suggests that the infrasonic waves (i.e., STADs) are mainly induced by the Rayleigh waves. The agreements in the travel time at various heights between the observation and theoretical calculation suggest that the STADs triggered by the vertical motion of ground surface caused by the Tohoku earthquake traveled vertically from the ground to the ionosphere with speed of the sound in the atmosphere over Taiwan. |
Marzo de 2016
Lithospheric flexure under the Hawaiian volcanic load: internal stresses and a broken plate revealed by earthquakes
Author: Fred W. Klein
Link: Click here
Abstract
Several lines of earthquake evidence indicate the lithospheric plate is broken under the load of the Island of Hawai'i, where the geometry of the lithosphere is circular with a central depression. The plate bends concave downward surrounding a stress-free hole, rather than bending concave upward as with past assumptions. Earthquake focal mechanisms show that the center of load stress and the weak hole is between the summits of Mauna Loa and Mauna Kea where the load is greatest. The earthquake gap at 21 km depth coincides with the predicted neutral plane of flexure where horizontal stress changes sign. Focal mechanism P-axes below the neutral plane display a striking radial pattern pointing to the |
stress center. Earthquakes above the neutral plane in the north part of the island have opposite stress patterns: T-axes tend to be radial. The M6.2 Honomu and M6.7 Kiholo mainshocks (both at 39 km depth) are below the neutral plane and show radial compression, and the M6.0 Kiholo aftershock above the neutral plane has tangential compression. Earthquakes deeper than 20 km define a donut of seismicity around the stress center where flexural bending is a maximum. The hole is interpreted as the soft center where the lithospheric plate is broken. Kilauea's deep conduit is seismically active because it is in the ring of maximum bending. A simplified two-dimensional stress model for a bending slab with a load at one end yields stress orientations that agree with earthquake stress axes and radial P axes below the neutral plane. A previous inversion of deep Hawaiian focal mechanisms found a circular solution around the stress center that agrees with the model. For horizontal faults, the shear stress within the bending slab matches the slip in the deep Kilauea seismic zone and enhances outward slip of active flanks. |
Marzo de 2016
Seismo-Electromagnetic Thin-Bed Responses: Natural Signal Enhancements?
Authors: N. Grobbe and E.C. Slob
Link: Click here
Abstract
We study if nature can help us overcome the very low signal-to-noise ratio of seismo-electromagnetic converted fields by investigating the effects of thin-bed geological structures on the seismo-electromagnetic signal. To investigate the effects of bed-thinning on the seismo-electromagnetic interference patterns, we numerically simulate seismo-electromagnetic wave propagation through horizontally layered media with different amounts and thicknesses of thin-beds. We distinguish two limits of bed thickness. Below the upper limit, the package of thin-beds starts acting like an ‘effective’ medium. Below the lower limit, further thinning does not affect the seismo-electromagnetic interface response signal strength anymore. We demonstrate seismo-electromagnetic sensitivity |
to changes in medium parameters on a spatial scale much smaller than the seismic resolution. Increasing amounts of thin-beds can cause the interface response signal strength to increase or decrease. Whether constructive or destructive interference occurs seems to be dependent on the seismo-electromagnetic coupling coefficient contrasts. When the combined result of the contrast, between upper halfspace and package of thin-beds, and the internal thin-bed contrast, is positive, constructive interference occurs. Destructive interference occurs when the combined contrast is negative. Maximum amplitude tuning occurs for thicknesses of thin-bed packages similar to the dominant pressure- and shear wavelengths. Artefacts due to model periodicity are excluded by comparing periodic media with random models. By simulating moving oil/water contacts during production, where the oil layer is gradually being thinned, seismo-electromagnetic signals are proven very sensitive to oil/water contacts. An oil layer with a thickness of less than one percent of the dominant shear wavelength is still recognized. |
Marzo de 2016
Timing of deformation in the Sarandí del Yí Shear Zone, Uruguay: implications for the amalgamation of Western Gondwana during the Neoproterozoic Brasiliano–Pan-African Orogeny
Authors: Sebastián Oriolo, Pedro Oyhantçabal et al
Link: Click here
Abstract
U–Pb and Hf zircon (SHRIMP and LA–ICP–MS), Ar/Ar hornblende and muscovite, and Rb–Sr whole rock–muscovite isochron data from the mylonites of the Sarandí del Yí Shear Zone, Uruguay, were obtained in order to assess the tectonothermal evolution of this crustal–scale structure. Integration of these results with available kinematic, structural and microstructural data of the shear zone as well as with geochronological data from the adjacent blocks allowed to constrain the onset of deformation along the shear zone at |
630–625 Ma during the collision of the Nico Pérez Terrane and the Río de la Plata Craton. The shear zone underwent dextral shearing up to 596 Ma under upper– to middle–amphibolite facies conditions, which was succeeded by sinistral shearing under lower–amphibolite to upper–greenschist facies conditions until at least 584 Ma. After emplacement of the Cerro Caperuza granite at 570 Ma, the shear zone underwent only cataclastic deformation between the late Ediacaran and the Cambrian. The Sarandí del Yí Shear Zone is thus related to the syn– to post–collisional evolution of the amalgamation of the Río de la Plata Craton and the Nico Pérez Terrane. Furthermore, the obtained data reveal that strain partitioning and localization with time, magmatism emplacement and fluid circulation are key processes affecting the isotopic systems in mylonitic belts, revealing the complexity in assessing the age of deformation of long–lived shear zones. |
Marzo de 2016
Volcanic lightning and plume behavior reveal evolving hazards during the April 2015 eruption of Calbuco volcano, Chile
Authors: Alexa R. Van Eaton, Álvaro Amigo et al
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Link: Click here |
Marzo de 2016
Ongoing deformation of Antarctica following recent Great Earthquakes
Authors: Matt A. King and Alvaro Santamaría-Gómez
Link: Click here
Abstract
Antarctica's secular motion is thought to be almost everywhere governed by horizontal rigid plate rotation plus three-dimensional deformations due to past and present changes in ice ocean loading, known as glacial isostatic adjustment (GIA). We use geodetic data to investigate deformation following the 1998 M ~8.2 Antarctic intraplate |
Earthquake and show sustained three-dimensional deformation along East Antarctica's coastline, 600 km from the rupture location. Using a model of viscoelastic deformation, we are able to match observed northward velocity changes, and either east or height, but not all three directions simultaneously, apparently partly due to lateral variations in mantle rheology. Our modeling predicts that much of Antarctica may still be deforming, with further deformation possible from the 2004 M 8 Macquarie Ridge Earthquake. This previously unconsidered mode of Antarctic deformation affects geodetic estimates of plate motion and GIA; its viscous nature raises the prospect of further present-day deformation due to earlier Great Earthquakes. |
Marzo de 2016
Using a genetic algorithm to estimate the details of earthquake slip distributions from point surface displacements
Authors:
A. Lindsay, J. McCloskey et al
Link: Click here
Abstract
Examining fault activity over several earthquake cycles is necessary for long-term modeling of the fault strain budget and stress state. While this requires knowledge of coseismic slip distributions for successive earthquakes along the fault, these exist only for the most recent events. However, overlying the Sunda Trench, sparsely distributed coral microatolls are sensitive to tectonically induced changes in relative sea levels and provide a century-spanning paleogeodetic and paleoseismic record. Here we present a new technique called the Genetic Algorithm Slip Estimator to constrain slip distributions from observed surface deformations of corals. We identify a suite of models consistent
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with the observations, and from them we compute an ensemble estimate of the causative slip. We systematically test our technique using synthetic data. Applying the technique to observed coral displacements for the 2005 Nias-Simeulue earthquake and 2007 Mentawai sequence, we reproduce key features of slip present in previously published inversions such as the magnitude and location of slip asperities. From the displacement data available for the 1797 and 1833 Mentawai earthquakes, we present slip estimates reproducing observed displacements. The areas of highest modeled slip in the paleoearthquake are nonoverlapping, and our solutions appear to tile the plate interface, complementing one another. This observation is supported by the complex rupture pattern of the 2007 Mentawai sequence, underlining the need to examine earthquake occurrence through long-term strain budget and stress modeling. Although developed to estimate earthquake slip, the technique is readily adaptable for a wider range of applications. |
Marzo de 2016
On the ratio of dynamic topography and gravity anomalies in a dynamic Earth
Authors: L. Colli, S. Ghelichkhan et al
Link: Click here
Abstract
Growing evidence from a variety of geologic indicators points to significant topography maintained convectively by viscous stresses in the mantle. However, while gravity is sensitive to dynamically supported topography, there are only small free-air gravity anomalies (<30 mGal) associated with Earth's long-wavelength topography. This has been used to suggest that surface heights computed assuming a complete isostatic equilibrium provide a good approximation to observed topography. Here we show that the apparent paradox is resolved by the well-established formalism of global, self-gravitating, viscously stratified Earth models. The models predict a complex relation between dynamic topography, mass and gravity anomalies that is not summarized by a constant admittance — i.e., ratio of gravity anomalies to surface deflections — as one would infer from analytic flow solutions formulated in a half space. Our results suggest that sizable dynamic topography may exist without a corresponding gravity signal. |
Marzo de 2016
Lithospheric flexure and gravity spreading of Olympus Mons volcano, Mars
Authors: S. Musiol, E. P. Holohan et al
Link: Click here
Abstract
The structural architecture of large volcanoes is governed substantially by gravity-driven deformation that is manifest as distinct processes such as basement flexure or volcanic spreading. Temporal effects and the mutual interplay of these processes have been investigated only to a limited extent, and so we present novel numerical models of the time-dependent deformation associated with them. The models simulate the combined effects of lithospheric flexure and volcanic spreading during growth increments of an elastoplastic volcanic cone. Different spreading scenarios are considered by a variable coupling decoupling behavior at the interface between volcano and basement. We apply our models to Olympus Mons on Mars, which is characterized by upper to middle flank terraces on the shield, is encircled by a basal scarp that has an average slope of 30° and is surrounded by distant deposits that resemble large-scale slumping features on Earth. Our results are consistent with the interpretation (...) |
Marzo de 2016
Simulated long-term climate response to idealized solar geoengineering
Authors:Long Cao, Lei Duan et al
Link: Click here
Abstract
Solar geoengineering has been proposed as a potential means to counteract anthropogenic climate change, yet it is unknown how such climate intervention might affect the Earth's climate on the millennial time scale. Here we use the HadCM3L model to conduct a 1000-year sunshade geoengineering simulation in which solar irradiance is uniformly reduced by 4% to |
approximately offset global mean warming from an abrupt quadrupling of atmospheric CO2. During the 1000-year period, modeled global climate, including temperature, hydrological cycle, and ocean circulation of the high-CO2 simulation departs substantially from that of the control preindustrial simulation, whereas the climate of the geoengineering simulation remains much closer to that of the preindustrial state with little drift. The results of our study do not support the hypothesis that non-linearities in the climate system would cause substantial drift in the climate system if solar geoengineering were to be deployed on the timescale of a millennium. |
Marzo de 2016
3D displacement field of the 2015 Mw8.3 Illapel earthquake (Chile) from across- and along-track Sentinel-1 TOPS interferometry
Authors: R. Grandin, E. Klein et al
Link: Click here
Abstract
Wide-swath imaging has become a standard acquisition mode for radar missions aiming at applying SAR interferometry at global scale with enhanced revisit frequency. Increased swath width, compared to classical Stripmap imaging mode, is achieved at the expense of azimuthal resolution. This makes along-track displacements, and subsequently north-south displacements, difficult to measure using
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conventional split-beam (multiple-aperture) InSAR or cross-correlation techniques. Alternatively, we show here that the along-track component of ground motion can be deduced from the double-difference between backward- and forward-looking interferograms within regions of burst overlap. “Burst overlap interferometry” takes advantage of the large squint angle diversity of Sentinel-1 (∼1°) to achieve sub-decimetric accuracy on the along-track component of ground motion. We demonstrate the efficiency of this method using Sentinel-1 data covering the 2015 Mw8.3 Illapel earthquake (Chile) for which we retrieve the full 3D displacement field and validate it against observations from a dense network of GPS sensors. |
Marzo de 2016
Aeromagnetic investigation of southern Calabria and the Messina Straits (Italy): Tracking seismogenic sources of 1783 and 1908 earthquakes
Authors:Liliana Minelli, Antonio Vecchio et al
Link: Click here
Abstract
Southern Calabria and the NE corner of Sicily (Italy) were struck in 1783 and 1908 A.D. by two of the most catastrophic earthquakes ever in European history. Although it is generally acknowledged that the seisms were yielded by normal faults rupturing the upper crust of the Calabria-Peloritani terrane, no consensus exists on seismogenic source location and orientation. Here we report on a high-resolution low-altitude aeromagnetic survey of southern Calabria and Messina Straits. In southern Calabria we document a broad weakly positive (5–10 nT) |
anomaly zone interrupted by three en echelon SW-NE null to negative magnetic anomaly corridors. Euler deconvolution and magnetic modeling show that the anomaly pattern is produced by a 1–1.5 km thick crustal “layer” located within 3 km depth. This layer is offset by a 25 km long NE trending fault that corresponds to the Armo normal fault, recently inferred to be the source for the 1908 earthquake. Few kilometers to the south, we also document a subparallel and previously unrecognized fault, entering the Messina Straits and likely joining the Armo fault at depth. Further east, we model a 40 km long normal fault, probably extending northeastward for additional 40 km, running along the south Calabria axis from Aspromonte to the Serre mountains and partly following the 18 km long surface rupture witnessed by Déodat de Dolomieu after the 1783 earthquake. Thus, aeromagnetic data suggest that the sources of the 1783 and 1908 earthquakes are en echelon faults belonging to the same NW dipping normal fault system straddling the whole southern Calabria. |
Marzo de 2016
Using a genetic algorithm to estimate the details of earthquake slip distributions from point surface displacements
Authors: A. Lindsay, J. McCloskey et al
Link: Click here
Abstract
Examining fault activity over several earthquake cycles is necessary for long-term modeling of the fault strain budget and stress state. While this requires knowledge of coseismic slip distributions for successive earthquakes along the fault, these exist only for the most recent events. However, overlying the Sunda Trench, sparsely distributed coral microatolls are sensitive to tectonically induced changes in relative sea levels and provide a century-spanning paleogeodetic and paleoseismic record. Here we present a new technique called the Genetic Algorithm Slip Estimator to constrain slip distributions from observed surface deformations |
of corals. We identify a suite of models consistent with the observations, and from them we compute an ensemble estimate of the causative slip. We systematically test our technique using synthetic data. Applying the technique to observed coral displacements for the 2005 Nias-Simeulue earthquake and 2007 Mentawai sequence, we reproduce key features of slip present in previously published inversions such as the magnitude and location of slip asperities. From the displacement data available for the 1797 and 1833 Mentawai earthquakes, we present slip estimates reproducing observed displacements. The areas of highest modeled slip in the paleoearthquake are nonoverlapping, and our solutions appear to tile the plate interface, complementing one another. This observation is supported by the complex rupture pattern of the 2007 Mentawai sequence, underlining the need to examine earthquake occurrence through long-term strain budget and stress modeling. Although developed to estimate earthquake slip, the technique is readily adaptable for a wider range of applications. |
Marzo de 2016
Fault interactions and triggering during the 10 January 2012 Mw 7.2 Sumatra earthquake
Authors: Wenyuan Fan and Peter M. Shearer
Link: Click here
Abstract
The 10 January 2012 Mw 7.2 Sumatra earthquake in the Wharton basin occurred 3 months before the great Mw 8.6 and Mw 8.2 earthquakes in the same region, which had complex ruptures and are the largest strike-slip earthquakes ever recorded. Teleseismic P wave back projection of the Mw 7.2 earthquake images a unilateral rupture lasting ∼40 s without observable frequency dependency (low frequency, 0.05–0.3 Hz, high frequency, 0.3–1 Hz). In addition to radiation bursts during the Mw 7.2 main shock, coherent energy releases from 50 to 75 s and from 100 to 125 s are observed about
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143 km northeast of the main shock rupture and landward of the trench. Analysis of globally recorded P waves, in both 0.02–0.05 Hz velocity records and 1–5 Hz stacked envelope functions, confirms the presence of coherent sources during the time windows. The observed energy bursts are likely to be large early aftershocks occurring on or near the subduction interface. Both dynamic and static triggering could have induced these early aftershocks, as they initiated after the surface wave passed by, and the Coulomb stress perturbations from the Mw 7.2 main shock promote earthquakes in the observed locations. The earthquake sequence is a clear example of a seaward-intraplate strike-slip earthquake triggering landward-intraplate earthquakes in the same region, in contrast to previously reported normal-reverse or reverse-normal interactions at subduction zones. |
Marzo de 2016
A MATLAB toolbox and Excel workbook for calculating the densities, seismic wave speeds, and major element composition of minerals and rocks at pressure and temperature
Authors: Geoffrey A. Abers and Bradley R. Hacker
Link: Click here
Abstract
To interpret seismic images, rock seismic velocities need to be calculated at elevated pressure and temperature for arbitrary compositions. This technical report describes an algorithm, software, and data to make such |
calculations from the physical properties of minerals. It updates a previous compilation and Excel® spreadsheet and includes new MATLAB® tools for the calculations. The database of 60 mineral end-members includes all parameters needed to estimate density and elastic moduli for many crustal and mantle rocks at conditions relevant to the upper few hundreds of kilometers of Earth. The behavior of α and β quartz is treated as a special case, owing to its unusual Poisson's ratio and thermal expansion that vary rapidly near the α-β transition. The MATLAB tools allow integration of these calculations into a variety of modeling and data analysis projects. |
Marzo de 2016
Rapid automated W-phase slip inversion for the Illapel great earthquake (2015, Mw = 8.3)
Authors: Roberto Benavente, Phil R. Cummins et al
Link: Click here
Abstract
We perform rapid W-phase finite fault inversion for the 2015 Illapel great earthquake (Mw = 8.3). To evaluate the performance of the inversion in a near real time context, we divide seismic stations into four groups. The groups consider stations up to epicentral distances of 30°, 50°, 75°, and 90°, |
respectively. The results for the first group could have been available within 25 min after the origin time and the results for the last group within 1 h. The four results consistently show a peak slip of ∼10 m near the trench with trench perpendicular rake which is consistent with the tsunami genesis of the event. The slip location is similar to that in the preliminary U.S. Geological Survey solution. The inversion is automated and provides meaningful results within 25 min after the event. This makes the method particularly suited to emergency management and early warning at regional and teletsunami distances. |
Marzo de 2016
The role of a mantle plume in the formation of Yellowstone volcanism
Authors: Tiffany Leonard and Lijun Liu
Link: Click here
Abstract
The origin of the Yellowstone volcanic province remains debated. Proposed hypotheses involve either a mantle plume or not. Recent tomographic images allow a quantitative evaluation of the plume hypothesis and its interaction with the Farallon slabs. Using 4-D geodynamic models |
with data assimilation, we find that the slab is always in the way of the initially rising plume and that the plume could reach the surface only through the broken slab hinge at ~15 Ma. For most of the time, the sinking slabs dominate the mantle flow and prohibit upwelling. We find that a plume that satisfies the present mantle image beneath Yellowstone fails to predict both voluminous hot materials at shallow depths beneath the western U.S. and the age migration of the hot spot tracks. We suggest that a plume is likely to have much less influence on the Yellowstone volcanism than previously thought. |
Marzo de 2016
Millenary Mw > 9.0 earthquakes required by geodetic strain in the Himalaya
Authors: V. L. Stevens and J.-P. Avouac
Link: Click here
Abstract
The Himalayan arc produced the largest known continental earthquake, the Mw ≈ 8.7 Assam earthquake of 1950, but how frequently and where else in the Himalaya such large-magnitude earthquakes occur is not known. Paleoseismic evidence for coseismic ruptures at the front of the |
Himalaya with 15 to 30 m of slip suggests even larger events in medieval times, but this inference is debated. Here we estimate the frequency and magnitude of the largest earthquake in the Himalaya needed so that the moment released by seismicity balances the deficit of moment derived from measurements of geodetic strain. Assuming one third of the moment buildup is released aseismically and the earthquakes roughly follow a Gutenberg-Richter distribution, we find that Mw > 9.0 events are needed with a confidence level of at least 60% and must return approximately once per 800 years on average. |
Marzo de 2016
Short-term probabilistic earthquake risk assessment considering time-dependent b values
Authors: Laura Gulia, Thessa Thormann et al
Link: Click here
Abstract
Laboratory experiments highlight a systematic b value decrease during the stress increase period before failure, and some large natural events are known to show a precursory decrease in the b value. However, short-term forecast models currently consider only the generic probability that |
an event can trigger subsequent seismicity in the near field. While the probability increase over a stationary Poissonian background is substantial, selected case studies have shown through cost-benefit analysis that the absolute main shock probability remains too low to warrant significant mitigation actions. We analyze the probabilities considering both changes in the seismicity rates and temporal changes in the b value. The precursory b value decrease in the 2009 L'Aquila case results in an additional fiftyfold probability increase for a M6.3 event. Translated into time-varying hazard and risk, these changes surpass the cost-benefit threshold for short-term evacuation. |
Marzo de 2016
Slip segmentation and slow rupture to the trench during the 2015, Mw8.3 Illapel, Chile earthquake
Authors: Diego Melgar, Wenyuan Fan et al
Link: Click here
Abstract
The 2015 Mw8.3 Illapel, Chile earthquake is the latest megathrust event on the central segment of that subduction zone. It generated strong ground motions and a large (up to 11 m runup) tsunami which prompted the evacuation of more than 1 million people in the first hours following the event. Observations during recent earthquakes suggest that these phenomena can be associated with rupture on different parts of the megathrust. The deep portion generates strong shaking while slow, large slip on the shallow fault |
is responsible for the tsunami. It is unclear whether all megathrusts can have shallow slip during coseismic rupture and what physical properties regulate this. Here we show that the Illapel event ruptured both deep and shallow segments with substantial slip. We resolve a kinematic slip model using regional geophysical observations and analyze it jointly with teleseismic backprojection. We find that the shallow and deep portions of the megathrust are segmented and have fundamentally different behavior. We forward calculate local tsunami propagation from the resolved slip and find good agreement with field measurements, independently validating the slip model. These results show that the central portion of the Chilean subduction zone has accumulated a significant shallow slip deficit and indicates that, given enough time, shallow slip might be possible everywhere along the subduction zone. |
Marzo de 2016
Multiparametric observation of volcanic lightning: Sakurajima volcano, Japan
Authors: C. Cimarelli, M.A. Alatorre-Ibargüengoitia et al
Link: Click here
Abstract
We recorded volcanic lightning generated by Vulcanian explosions at Sakurajima volcano using a synchronized multiparametric array. Physical properties of lightning are related to plume dynamics and associated electromagnetic field variations are revealed by video observations (high- and normal-speed) together with infrasound and high sampling-rate |
magnetotelluric signals. Data show that volcanic lightning at Sakurajima mainly occurs in the plume gas-thrust region at a few hundred meters above the crater rim, where the overpressure of the turbulent volcanic jets determines the electrification of particles generating a complex charge structure in the growing plume. Organization of charges may be achieved at later stages when the plume transitions from the jet phase to the convective phase. Comparison with atmospheric sounding and maximum plume height data show that the effect of hydrometeors on flash generation at Sakurajima is negligible and can be more prudently considered as an additional factor contributing to the electrification of volcanic plumes. |
Marzo de 2016
Coseismic radiation and stress drop during the 2015 Mw 8.3 Illapel, Chile megathrust earthquake
Authors: Jiuxun Yin, Hongfeng Yang et al
Link: Click here
Abstract
On 16 September 2015, an Mw 8.3 earthquake struck middle Chile due to the subduction of the Nazca plate beneath the South America plate. This earthquake is the consequence of 72 years of strain accumulation in the region since the 1943 M 8.3 event. In this study, we apply the compressive sensing method (CS) to invert for the spatiotemporal distribution of the coseismic radiation at different frequencies of this event. The results show clear frequency-dependent feature of earthquake rupture with low-frequency (LF) radiation located in the updip region while high-frequency (HF) radiation concentrated in the |
downdip region of the megathrust. We also compare the CS results with three coseismic slip models as well as the stress drop distributions inferred from these slip models. The comparison confirms our understanding of coseismic radiation that energy sources are mostly located in the margin of large coseismic slip regions. Furthermore, we find that the LF radiation sources are mainly within the stress-decreasing (releasing) regions while the HF radiation sources are mainly located in the stress-increasing (loading) regions due to rupturing of relatively large asperities nearby (stress decreasing and releasing). These results help to better understand the physics of the rupture process during megathrust earthquakes. Moreover, our results do not show radiation sources south of the epicenter, suggesting that the subducting Juan Fernandez Ridge probably stopped the rupture of this earthquake toward the south. |
Marzo de 2016
The vertical propagation of disturbances triggered by seismic waves of the 11 March 2011 M9.0 Tohoku earthquake over Taiwan
Authors: J. Y. Liu, C. H. Chen et al
Link: Click here
Abstract
In this paper, concurrent/colocated measurements of seismometers, infrasonic systems, magnetometers, HF-CW (high frequency-continuous wave) Doppler sounding systems, and GPS receivers are employed to detect disturbances triggered by seismic waves of the 11 March 2011 M9.0 Tohoku earthquake. No time delay between colocated infrasonic (i.e., super long acoustic) waves and seismic waves indicates that the triggered acoustic and/or gravity |
waves in the atmosphere (or seismo-traveling atmospheric disturbances, STADs) near the Earth's surface can be immediately activated by vertical ground motions. The circle method is used to find the origin and compute the observed horizontal traveling speed of the triggered infrasonic waves. The speed of about 3.3 km/s computed from the arrival time versus the epicentral distance suggests that the infrasonic waves (i.e., STADs) are mainly induced by the Rayleigh waves. The agreements in the travel time at various heights between the observation and theoretical calculation suggest that the STADs triggered by the vertical motion of ground surface caused by the Tohoku earthquake traveled vertically from the ground to the ionosphere with speed of the sound in the atmosphere over Taiwan. |
Febrero de 2016
Air quality forecasting for winter-time PM2.5 episodes occurring in multiple cities in central and southern Chile
Authors: Pablo E. Saide, Marcelo Mena-Carrasco et al
Link: Click here
Abstract
Episodic air quality degradation due to particles occurs in multiple cities in central and southern Chile during the austral winter reaching levels up to 300800 µg/m3 hourly PM2.5, which can be associated with severe effects on human health. An air quality prediction system is developed to predict such events in near real time up to 3 days in advance for nine cities with regular air quality monitoring: Santiago, Rancagua, Curicó, Talca, Chillan, Los Ángeles, Temuco, Valdivia, and Osorno. The system uses the Weather Research and Forecasting with Chemistry model configured with a nested 2 km grid-spacing domain to predict |
weather and inert tracers. The tracers are converted to hourly PM2.5concentrations using an observationally based calibration which is substantially less computationally intensive than a full chemistry model. The conversion takes into account processes occurring in these cities, including higher likelihood of episode occurrence during weekends and during colder days, the latter related to increased wood-burning-stove activity for heating. The system is calibrated and evaluated for AprilAugust 2014 where it has an overall skill of 5372% of episodes accurately forecasted (6176% for the best initialization) which is better than persistence for most stations. Forecasts one, two, and three days in advance all have skill in forecasting events but often present large variability within them due to different meteorological initializations. The system is being implemented in Chile to assist authority decisions not only to warn the population but also to take contingency-based emission restrictions to try to avoid severe pollution events. |
Febrero de 2016
Reconstructing input for artificial neural networks based on embedding theory and mutual information to simulate soil pore water salinity in tidal floodplain
Authors: Fawen Zheng, Yongshan Wan et al
Link: Click here
Abstract
Soil pore water salinity plays an important role in the distribution of vegetation and biogeochemical processes in coastal floodplain ecosystems. In this study, artificial neural networks (ANNs) were applied to simulate the pore water salinity of a tidal floodplain in Florida. We present an approach based on embedding theory with mutual information to reconstruct ANN model input time series from one system state variable. Mutual information between system output and input was computed and the local minimum mutual information points were used to determine a time lag vector for time series embedding and |
reconstruction, with which the mutual information weighted average method was developed to compute the components of reconstructed time series. The optimal embedding dimension was obtained by optimizing model performance. The method was applied to simulate soil pore water salinity dynamics at 12 probe locations in the tidal floodplain influenced by saltwater intrusion using 4 years (2005–2008) data, in which adjacent river water salinity was used to reconstruct model input. The simulated electrical conductivity of the pore water showed close agreement with field observations (RMSE inline image and inline image), suggesting the reconstructed input by the proposed approach provided adequate input information for ANN modeling. Multiple linear regression model, partial mutual information algorithm for input variable selection, k-NN algorithm, and simple time delay embedding were also used to further verify the merit of the proposed approach. |
Febrero de 2016
Is it possible that a gravity increase of 20 μGal yr−1 in southern Tibet comes from a wide-range density increase?
Authors: Shuang Yi, Qiuyu Wang et al
Link: Click here
Abstract
With absolute gravimetric observations from 2010 to 2013 in the southern Tibet, Chen et al. (2016) reported a gravity increase of up to 20 μGal/yr and concluded that it is possible if there was a density increase in a disk range of 580 km in diameter. Here we used observations from the gravity |
satellites Gravity Recovery and Climate Experiment (GRACE) over 12 years to evaluate whether the model was practical, because a mass accumulation in such a large spatial range is well within the detectability ability of GRACE. The gravity trend based on their model is orders of magnitude larger than the GRACE observation, thus negating its conclusions. We then evaluated contributions from seasonal variation, lakes, glaciers, rivers, precipitation, and snowfall and concluded that these factors cannot cause such a large gravity signal. Finally, we discussed some possible explanations for the gravity increase of 40 μGal in two years. |
Febrero de 2016
Scaling in natural and laboratory earthquakes
Authors: S. Nielsen, E. Spagnuolo et al
Link: Click here
Abstract
Laboratory experiments reproducing seismic slip conditions show extreme frictional weakening due to the activation of lubrication processes. Due to a substantial variability in the details of the weakening transient, generalization of experimental results and comparison to seismic observations have not been possible so far. Here |
we show that during the weakening, shear stress τ is generally well matched by a power law of slip u in the form inline image (with 0.35 < α < 0.6). The resulting fracture energy Gf can be approximated by a power law in some aspects in agreement with the seismological estimates inline image. It appears that Gf and inline image are comparable in the range 0.01 < u < 0.3 m. However, inline image surpasses Gf at larger slips: at u≈10 m, inline image and Gf≈106. Possible interpretations of this misfit involve the complexity of damage and weakening mechanisms within mature fault zone structures. |
Febrero de 2016
Discriminating induced seismicity from natural earthquakes using moment tensors and source spectra
Authors: Hongliang Zhang, David W. Eaton et al
Link: Click here
Abstract
Earthquake source mechanisms and spectra can provide important clues to aid in discriminating between natural and induced events. In this study, we calculate moment tensors and stress drop values for eight recent induced earthquakes in the Western Canadian Sedimentary Basin with magnitudes between 3.2 and 4.4, as well as a nearby magnitude 5.3 event that is interpreted as a natural earthquake. We calculate full moment tensor solutions by performing a waveform-fitting procedure based on a 1-D transversely isotropic velocity model. In addition to a dominant double-couple (DC) signature that is common to nearly all |
events, most induced events exhibit significant non-double-couple components. A parameter sensitivity analysis indicates that spurious non- DC components are negligible if the signal to noise ratio (SNR) exceeds 10 and if the 1-D model differs from the true velocity structure by less than 5%. Estimated focal depths of induced events are significantly shallower than the typical range of focal depths for intraplate earthquakes in the Canadian Shield. Stress drops of the eight induced events were estimated using a generalized spectral-fitting method and fall within the typical range of 2 to 90 MPa for tectonic earthquakes. Elastic moduli changes due to the brittle damage production at the source, presence of multiple intersecting fractures, dilatant jogs created at the overlapping areas of multiple fractures, or non-planar pre-existing faults may explain the non-DC components for induced events. |
Febrero de 2016
Hierarchical Bayesian method for mapping biogeochemical hot spots using induced polarization imaging
Authors: Haruko M. Wainwright, Adrian Flores Orozco et al
Link: Click here
Abstract
In floodplain environments, a naturally reduced zone (NRZ) is considered to be a common biogeochemical hot spot, having distinct microbial and geochemical characteristics. Although important for understanding their role in mediating floodplain biogeochemical processes, mapping the subsurface distribution of NRZs over the dimensions of a floodplain is challenging, as conventional wellbore data are typically spatially limited and the distribution of NRZs is heterogeneous. In this study, we present an innovative methodology for the probabilistic mapping of NRZs within a three-dimensional (3-D) subsurface domain using induced polarization imaging, which is a noninvasive geophysical technique. Measurements consist of surface |
geophysical surveys and drilling-recovered sediments at the U.S. Department of Energy field site near Rifle, CO (USA). Inversion of surface time domain-induced polarization (TDIP) data yielded 3-D images of the complex electrical resistivity, in terms of magnitude and phase, which are associated with mineral precipitation and other lithological properties. By extracting the TDIP data values colocated with wellbore lithological logs, we found that the NRZs have a different distribution of resistivity and polarization from the other aquifer sediments. To estimate the spatial distribution of NRZs, we developed a Bayesian hierarchical model to integrate the geophysical and wellbore data. In addition, the resistivity images were used to estimate hydrostratigraphic interfaces under the floodplain. Validation results showed that the integration of electrical imaging and wellbore data using a Bayesian hierarchical model was capable of mapping spatially heterogeneous interfaces and NRZ distributions thereby providing a minimally invasive means to parameterize a hydrobiogeochemical model of the floodplain. |
Febrero de 2016
Game theory and risk-based leveed river system planning with noncooperation
Authors: Rui Hui, Jay R. Lund et al
Link: Click here
Abstract
Optimal risk-based levee designs are usually developed for economic efficiency. However, in river systems with multiple levees, the planning and maintenance of different levees are controlled by different agencies or groups. For example, along many rivers, levees on opposite riverbanks constitute a simple leveed river system with each levee designed and controlled separately. Collaborative planning of the two levees can be economically optimal for the whole system. Independent and self-interested landholders on opposite riversides often are willing to separately determine their individual optimal levee plans, resulting in a less efficient leveed river system from an overall society-wide perspective (the tragedy of commons). We apply game theory to |
simple leveed river system planning where landholders on each riverside independently determine their optimal risk-based levee plans. Outcomes from noncooperative games are analyzed and compared with the overall economically optimal outcome, which minimizes net flood cost system-wide. The system-wide economically optimal solution generally transfers residual flood risk to the lower-valued side of the river, but is often impractical without compensating for flood risk transfer to improve outcomes for all individuals involved. Such compensation can be determined and implemented with landholders' agreements on collaboration to develop an economically optimal plan. By examining iterative multiple-shot noncooperative games with reversible and irreversible decisions, the costs of myopia for the future in making levee planning decisions show the significance of considering the externalities and evolution path of dynamic water resource problems to improve decision-making. |
Febrero de 2016
Short-term probabilistic earthquake risk assessment considering time-dependent b values
Authors: Laura Gulia, Thessa Tormann et al
Link: Click here
Abstract
Laboratory experiments highlight a systematic b value decrease during the stress increase period before failure, and some large natural events are known to show a precursory decrease in the b value. However, short-term forecast models currently consider only the generic probability that |
an event can trigger subsequent seismicity in the near field. While the probability increase over a stationary Poissonian background is substantial, selected case studies have shown through cost-benefit analysis that the absolute main shock probability remains too low to warrant significant mitigation actions. We analyze the probabilities considering both changes in the seismicity rates and temporal changes in the b value. The precursory b value decrease in the 2009 L'Aquila case results in an additional fiftyfold probability increase for a M6.3 event. Translated into time-varying hazard and risk, these changes surpass the cost-benefit threshold for short-term evacuation. |
Febrero de 2016
Rapid automated W-phase slip inversion for the Illapel great earthquake (2015, Mw = 8.3)
Authors: Roberto Benavente, Phil R. Cummins et al
Link: Click here
Abstract
We perform rapid W-phase finite fault inversion for the 2015 Illapel great earthquake (Mw = 8.3). To evaluate the performance of the inversion in a near real time context, we divide seismic stations into 4 groups. The groups consider stations up to epicentral distances of 30o, 50o, 75o and 90o, |
respectively. The results for the first group could have been available within 25 minutes after the origin time and the results for the last group within 1 hour. The 4 results consistently show a peak slip of ∼10 m near the trench with trench perpendicular rake which is consistent with the tsunami genesis of the event. The slip location is similar to that in the preliminary USGS solution. The inversion is automated and provides meaningful results within 25 minutes after the event. This makes the method particularly suited to emergency management and early warning at regional and teletsunami distances. |
Febrero de 2016
The 2015 Illapel earthquake, central Chile: A type case for a characteristic earthquake?
Authors: F. Tilmann, Y. Zhang et al
Link: Click here
Abstract
On 16 September 2015, the MW = 8.2 Illapel megathrust earthquake ruptured the Central Chilean margin. Combining inversions of displacement measurements and seismic waveforms with high frequency (HF) teleseismic backprojection, we derive a comprehensive description of the rupture, which also predicts deep ocean tsunami wave heights. We further
|
determine moment tensors and obtain accurate depth estimates for the aftershock sequence. The earthquake nucleated near the coast but then propagated to the north and updip, attaining a peak slip of 5–6 m. In contrast, HF seismic radiation is mostly emitted downdip of the region of intense slip and arrests earlier than the long period rupture, indicating smooth slip along the shallow plate interface in the final phase. A superficially similar earthquake in 1943 with a similar aftershock zone had a much shorter source time function, which matches the duration of HF seismic radiation in the recent event, indicating that the 1943 event lacked the shallow slip. |
Febrero de 2016
Modeling of the coseismic electromagnetic fields observed during the 2004 Mw 6.0 Parkfield earthquake
Authors: Yongxin Gao, Jerry M. Harris et al
Link: Click here
Abstract
The coseismic electromagnetic signals observed during the 2004 Mw 6 Parkfield earthquake are simulated using electrokinetic theory. By using a finite fault source model obtained via kinematic inversion, we calculate the electric and magnetic responses to the earthquake rupture. The result shows that the synthetic electric signals agree
|
with the observed data for both amplitude and wave shape, especially for early portions of the records (first 9 s) after the earthquake, supporting the electrokinetic effect as the reasonable mechanism for the generation of the coseismic electric fields. More work is needed to explain the magnetic fields and the later portions of the electric fields. Analysis shows that the coseismic electromagnetic (EM) signals are sensitive to both the material properties at the location of the EM sensors and the electrochemical heterogeneity in the vicinity of the EM sensors and can be used to characterize the underground electrochemical properties. |
Febrero de 2016
Source model of the 16 September 2015 Illapel, Chile, Mw 8.4 earthquake based on teleseismic and tsunami data
Authors: Mohammad Heidarzadeh, Satoko Murotani et al
Link: Click here
Abstract
We proposed a source model for the 16 September 2015 Illapel (Chile) tsunamigenic earthquake using teleseismic and tsunami data. The 2015 epicenter was at the northernmost of the aftershocks zone of the 2010 Mw 8.8 Maule earthquake. Teleseismic body wave inversions |
and tsunami simulations showed optimum
rupture velocities of 1.5–2.0 km/s. The agreement between observed and synthetic waveforms was quantified using normalized root-mean-square (NRMS) misfit. The variations of NRMS misfits were larger for tsunami data compared to the teleseismic data, because tsunami waveforms are more sensitive to the spatial distribution of slip. The large-slip area was 80 km (along strike) × 100 km (along dip) with an average slip of 5.0 m and depth of 12–33 km, located ~70 km to the northwest of the epicenter. We obtained a seismic moment of 4.42 × 1021 Nm equivalent to Mw 8.4. Results may indicate a northward stress transfer from the 2010 Maule earthquake. |
Febrero de 2016
Source estimate and tsunami forecast from far-field deep-ocean tsunami waveforms—The 27 February 2010 Mw 8.8 Maule earthquake
Authors: Masahiro Yoshimoto, Shingo Watada et al
Link: Click here
Abstract
We inverted the 2010 Maule earthquake tsunami waveforms recorded at DART (Deep-ocean Assessment and Reporting Tsunamis) stations in the Pacific Ocean by taking into account the effects of the seawater compressibility, elasticity of the solid Earth, and gravitational potential change.
|
These effects slow down the tsunami speed and consequently move the slip offshore or updip direction, consistent with the slip distribution obtained by a joint inversion of DART, tide gauge, GPS, and coastal geodetic data. Separate inversions of only near-field DART data and only far-field DART data produce similar slip distributions. The former demonstrates that accurate tsunami arrival times and waveforms of trans-Pacific tsunamis can be forecast in real time. The latter indicates that if the tsunami source area is as large as the 2010 Maule earthquake, the tsunami source can be accurately estimated from the far-field deep-ocean tsunami records without near-field data. |
Febrero de 2016
Slip segmentation and slow rupture to the trench during the 2015, Mw8.3 Illapel, Chile earthquake
Authors: Diego Melgar, Wenyuan Fan et al
Link: Click here
Abstract
The 2015 Mw8.3 Illapel, Chile earthquake is the latest megathrust event on the central segment of that subduction zone. It generated strong ground motions and a large (up to 11 m runup) tsunami which prompted the evacuation of more than 1 million people in the first hours following the event. Observations during recent earthquakes suggest that these phenomena can be associated with rupture on different parts of the megathrust. The deep portion generates strong shaking while slow, large slip on the shallow fault |
is responsible for the tsunami. It is unclear whether all megathrusts can have shallow slip during coseismic rupture and what physical properties regulate this. Here we show that the Illapel event ruptured both deep and shallow segments with substantial slip. We resolve a kinematic slip model using regional geophysical observations and analyze it jointly with teleseismic backprojection. We find that the shallow and deep portions of the megathrust are segmented and have fundamentally different behavior. We forward calculate local tsunami propagation from the resolved slip and find good agreement with field measurements, independently validating the slip model. These results show that the central portion of the Chilean subduction zone has accumulated a significant shallow slip deficit and indicates that, given enough time, shallow slip might be possible everywhere along the subduction zone. |
Febrero de 2016
Periodic slow slip triggers megathrust zone earthquakes
in northeastern Japan
Authors: Naoki Uchida,Takeshi Iinuma et al
Link: Click here
Abstract
Both aseismic and seismic slip accommodate relative motion
across partially coupled plate-boundary faults. In northeastern
Japan, aseismic slip occurs in the form of decelerating afterslip
after large interplate earthquakes and as relatively steady
slip on uncoupled areas of the subduction
|
thrust. Here we report
on a previously unrecognized quasi-periodic slow-slip behavior
that is widespread in the megathrust zone. The repeat intervals
of the slow slip range from 1 to 6 years and often coincide
with or precede clusters of large [magnitude (M) ? 5] earthquakes,
including the 2011 M 9 Tohoku-oki earthquake. These results
suggest that inherently periodic slow-slip events result in
periodic stress perturbations and modulate the occurrence time
of larger earthquakes. The periodicity in the slow-slip rate
has the potential to help refine time-dependent earthquake forecasts. |
Febrero de 2016
Are there new findings in the search for ULF magnetic precursors
to earthquakes?
Authors: F. Masci et al
Link: Click here
Abstract
Moore (1964) in a letter published in Nature reported
disturbances in geomagnetic field data prior to the 27 March
1964 Alaska earthquake. After the publication of this report,
many papers have shown magnetic changes preceding earthquakes.
However, a causal relationship between preearthquake magnetic
changes and impending earthquakes has never been demonstrated.
As a consequence, after 50 years, magnetic disturbances in
the geomagnetic field are still candidate precursory phenomena.
Some researchers consider the investigation of ultra low frequency
(ULF: 0.00110 Hz) magnetic
|
data
the correct approach for identifying precursory signatures of
earthquakes. Other researchers, instead, have recently reviewed
many published ULF magnetic changes that preceded earthquakes
and have shown that these are not actual precursors. The recent
studies by Currie and Waters (2014) and Han et al. (2014) aim
to provide relevant new findings in the search for ULF magnetic
precursory signals. However, in order to contribute to science,
alleged precursors must be shown to be valid and reproducible
by objective testing. Here we will briefly discuss the state
of the art in the search for ULF magnetic precursors, paying
special attention to the recent findings of Currie and Waters
(2014) and Han et al. (2014). We do not see in these two reports
significant evidence that may support the observation of precursory
signatures of earthquakes in ULF magnetic records. |
Febrero de 2016
All-sky imaging of transglobal thermospheric gravity waves
generated by the March 2011 Tohoku Earthquake
Authors: Steven M. Smith, Carlos R. Martinis et al
Link: Click here
Abstract
We report on imaging measurements of thermospheric gravity
wave signatures in 630 nm
|
and
557.7 nm nightglow that suggest an association with the M
= 9 Tohoku (Japan) earthquake on 11 March 2011. The propagating
waves were recorded in all-sky images at the El Leoncito Observatory,
Argentina (31.8°S, 69.3°W), which is located 17,080
km from the earthquake epicenter, almost at the global antipodal
point. |
Enero de 2016
Slip segmentation and slow rupture to the trench during
the 2015, Mw8.3 Illapel, Chile earthquake
Authors: D Melgar, W Fan et al
Link: Click here
Abstract
The 2015 Mw8.3 Illapel, Chile earthquake is the latest
megathrust event on the central segment of that subduction
zone. It generated strong ground motions and a large (up to
11m runup) tsunami which prompted the evacuation of more than
1 million people in the first hours following the event. Observations
during recent earthquakes suggest that these phenomena can
be associated with rupture on different parts of the megathrust.
The deep portion generates strong shaking while slow, large
slip on the shallow fault is responsible for the tsunami.
It is unclear whether all megathrusts can have shallow
|
slip
during coseismic rupture and what physical properties regulate
this. Here we show that the Illapel event ruptured both deep
and shallow segments with substantial slip. We resolve a kinematic
slip model using regional geophysical observations and analyze
it jointly with teleseismic back-projection. We find that the
shallow and deep portions of the megathrust are segmented and
have fundamentally different behavior. We forward calculate
local tsunami propagation from the resolved slip model and find
good agreement with field measurements, independently validating
the slip model. These results show that the central portion
of the Chilean subduction zone has accumulated a significant
shallow slip deficit and indicates that, given enough time,
shallow slip might be possible everywhere along the subduction
zone. |
Enero
de 2016
Sistema antisísmico
Picunche
Académica descubrió posible sistema anti-sísmico
de la Iglesia de San Francisco
Fuente: Mario Arredondo / Comunicaciones FAU - Fotos: Natalia
Jorquera
Excavación en los cimientos del edificio, que son
parte de una investigación de la académica Natalia
Jorquera, permitió hallazgo de lo que podría
ser un disipador sísmico ideado por la población
prehispánica, y que sería la explicación
de que la iglesia se haya mantenido en pie a pesar de los
constantes sismos.
El proyecto FONDECYT Iniciación 11130628
"Rediscovering vernacular earthquake-resistant knowledge.
Identification and analysis of built best practice in Chilean
masonry architectural heritage", ha permitido a Natalia
Jorquera, académica del Departamento de Arquitectura,
Natalia Jorquera, analizar la reacción ante los sismos
de construcciones chilenas hechas en base a materiales de
tierra, adobe y caldurante los últimos tres años.
En ese contexto, llegó hasta la Iglesia y Convento
de San Francisco, ubicada en el centro de Santiago, para tratar
de dilucidar cómo es que el edificio ha resistido en
pie desde el inicio de su construcción en 1572 hasta
ahora, soportando los recurrentes terremotos que azotan al
país. El caso de la iglesia es especial en tanto es
la única construcción colonial que sigue en
pie con su estructura original en Chile.
|
Enero de 2016
The 2015 Illapel earthquake, central Chile: A type
case for a characteristic earthquake?
Authors: F Tilmann, Y Zhang et al
Link: Click here
Abstract
On 16 September 2015, the MW
= 8.2 Illapel megathrust earthquake ruptured the Central Chilean
margin. Combining inversions of displacement measurements
and seismic waveforms with high frequency (HF) teleseismic
backprojection, we derive a comprehensive description of the
rupture, which also predicts
|
deep ocean tsunami
wave heights. We further determine moment tensors and obtain
accurate depth estimates for the aftershock sequence. The earthquake
nucleated near the coast but then propagated to the north and
updip, attaining a peak slip of 5–6 m. In contrast,
HF seismic radiation is mostly emitted downdip of the region
of intense slip and arrests earlier than the long period rupture,
indicating smooth slip along the shallow plate interface in
the final phase. A superficially similar earthquake in 1943
with a similar aftershock zone had a much shorter source time
function, which matches the duration of HF seismic radiation
in the recent event, indicating that the 1943 event lacked the
shallow slip. |
Enero de 2016
Source model of the 16 September 2015 Illapel, Chile,
Mw 8.4 earthquake based on teleseismic
and tsunami data
Authors: M Heirdazadeh, S Murotani et al
Link: Click here
Abstract
We proposed a source model for the 16 September 2015 Illapel
(Chile) tsunamigenic earthquake using teleseismic and tsunami
data. The 2015 epicenter was at the northernmost of the aftershocks
zone of the 2010 Mw 8.8 Maule earthquake.
Teleseismic body wave inversions and tsunami simulations showed
optimum rupture velocities of 1.5–2.0 km/s. The
|
agreement
between observed and synthetic waveforms was quantified using
normalized root-mean-square (NRMS) misfit. The variations of
NRMS misfits were larger for tsunami data compared to the teleseismic
data, because tsunami waveforms are more sensitive to the spatial
distribution of slip. The large-slip area was 80 km (along
strike) × 100 km (along dip) with
an average slip of 5.0 m and depth of 12–33 km,
located ~70 km to the northwest of the epicenter. We
obtained a seismic moment of 4.42 × 1021 Nm
equivalent to Mw 8.4. Results may indicate
a northward stress transfer from the 2010 Maule earthquake. |
Enero de 2016
Smart phones could be used to detect earthquakes
Author: Emily Conover
Link: Click here
Abstract
The cellphone in your pocket could soon save you from
an earthquake. Researchers have shown that it is possible
to use GPS data from smart phones to detect tremors, potentially
providing an early warning system to those who have not yet
been hit.
"What’s really nice about this work is they are using
sensors that people carry around anyway," says geophysicist
Kristine Larson of the University of Colorado, Boulder. "It
could be very, very useful."
In the moments before an earthquake, a few extra
|
seconds can mean the difference between life and death. With
a little bit of warning, people can take shelter, nuclear
power plants can take last-minute precautions, and natural
gas utilities can shut down pipelines. Japan has an early
warning system that relies on more than 1000 seismometers
throughout the country, which saved lives during the magnitude-9
Tohoku earthquake that hit in 2011. A similar system exists
in Mexico, and another is under study in California. But such
systems are expensive and time-consuming to install and maintain,
making cellphones an attractive alternative, especially for
earthquake-prone countries in the developing world.
See
more (Science) >>
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Enero de 2016
Game theory and risk-based leveed river system planning with noncooperation
Authors: R Hui, JR Lund et al
Link: Click here
Abstract
Optimal risk-based levee designs are usually developed for economic efficiency. However, in river systems with multiple levees, the planning and maintenance of different levees are controlled by different agencies or groups. For example, along many rivers, levees on opposite riverbanks constitute a simple leveed river system with each levee designed and controlled separately. Collaborative planning of the two levees can be economically optimal for the whole system. Independent and self-interested landholders on opposite riversides often are willing to separately determine their individual optimal levee plans, resulting in a less efficient leveed river system from an overall society-wide perspective (the tragedy of commons). We apply game theory to simple leveed river system planning where |
landholders on each riverside independently determine their optimal risk-based levee plans. Outcomes from noncooperative games are analyzed and compared with the overall economically optimal outcome, which minimizes net flood cost system-wide. The system-wide economically optimal solution generally transfers residual flood risk to the lower-valued side of the river, but is often impractical without compensating for flood risk transfer to improve outcomes for all individuals involved. Such compensation can be determined and implemented with landholders' agreements on collaboration to develop an economically optimal plan. By examining iterative multiple-shot noncooperative games with reversible and irreversible decisions, the costs of myopia for the future in making levee planning decisions show the significance of considering the externalities and evolution path of dynamic water resource problems to improve decision-making. |
Enero de 2016
Delayed dynamic triggering: Local seismicity leading up to three remote M >= 6 aftershocks of the 11 April 2012 M8.6 Indian Ocean earthquake
Authors: CW Johnson et al
Link: Click here
Abstract
The 11 April 2012 M8.6 strike-slip Indian Ocean earthquake (IOE) was followed by an increase in global seismic activity, with three remote M ≥ 6.0 earthquakes within 24 h. We investigate delayed dynamic triggering by systematically examining three offshore regions hosting these events for changes in microseismic activity preceding the IOE, and during the hours between the IOE surface-wave arrival and the triggered-event candidate. The Blanco Fault Zone, USA, and the Tiburón Fault Zone, Mexico, each host a strike-slip event, and the Michoacán Subduction Zone, Mexico, hosts a reverse event. At these locations |
we estimate transient Coulomb stresses of ±1–10 kPa during the IOE. Each study area contains a regional seismic network allowing us to examine continuous waveforms at one or more nearby stations. We implement a short-/long-term-average algorithm and template matching to detect events and assess the seismicity with the β-statistic. Our results indicate low-magnitude seismicity in the days prior to the IOE and the occurrence of earthquakes during the surface-wave passage after more than 2 h of transient loading. We find both transtensional tectonic environments respond to the transient stresses with a substantial increase observed in the seismicity rates during the hours after the passage of surface waves. In contrast, seismicity rates remain constant in the subduction zone we investigate during the 14 h delay between the IOE and the large-magnitude earthquake. The seismicity rate increases we observe occur after many hours of dynamic stresses and suggest the long duration of transient loading initiated failure processes leading up to these M ≥ 6.0 events. |
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Enero de 2016
Geomorphic and geologic controls of geohazards induced by Nepal’s 2015 Gorkha earthquake
Authors: J. S. Kargel, G. J. Leonard et al
Link: Click here
Abstract
The Gorkha earthquake (magnitude 7.8) on 25 April 2015 and later aftershocks struck South Asia, killing ~9000 people and damaging a large region. Supported by a large campaign of responsive satellite data acquisitions over the earthquake disaster zone, our team undertook a satellite image survey of the earthquakes’ induced |
geohazards in Nepal and China and an assessment of the geomorphic, tectonic, and lithologic controls on quake-induced landslides. Timely analysis and communication aided response and recovery and informed decision-makers. We mapped 4312 coseismic and postseismic landslides. We also surveyed 491 glacier lakes for earthquake damage but found only nine landslide-impacted lakes and no visible satellite evidence of outbursts. Landslide densities correlate with slope, peak ground acceleration, surface downdrop, and specific metamorphic lithologies and large plutonic intrusions. |
Enero de 2016
Integrating solar energy and climate research into science education
Authors: Alan K Bets, J Hamilton et al
Link: Click here
Abstract
This paper analyzes multi-year records of solar flux and climate data
from two solar power sites in Vermont. We show the interannual
differences of temperature, wind, panel solar flux, electrical power
production and cloud cover. Power production has a linear relation to a
dimensionless measure of the transmission of sunlight through the cloud
field. The difference between panel and air temperatures reaches 24°C with high solar flux and low windspeed. High panel temperatures that occur in summer with low windspeeds and clear skies can reduce power production by as much as 13%. The |
intercomparison of two sites 63 km apart shows that while temperature is highly correlated on daily (R2=0.98) and hourly (R2=0.94) timescales, the correlation of panel solar flux drops markedly from daily (R2=0.86) to hourly (R2=0.63) timescales. Minimum temperatures change little with cloud cover, but the diurnal temperature range shows a nearly linear increase with falling cloud cover to 16°C under nearly clear skies, similar to results from the Canadian Prairies. The availability of these new solar and climate datasets allows local student groups, here a Rutland High School team, to explore the coupled relationships between climate, clouds and renewable power production. As our society makes major changes in our energy infrastructure in response to climate change, it is important that we accelerate the technical education of high school students using real-world data. |
Enero de 2016
Core solidification and dynamo evolution in a mantle-stripped planetesimal
Authors: A Scheinberg, L T Elkins-Tanton et al
Link: Click here
Abstract
The physical processes active during the crystallization of a
low-pressure, low-gravity planetesimal core are poorly understood but
have implications for asteroidal magnetic fields and large-scale
asteroidal structure. We consider a core with only a thin silicate
shell, which could be |
analogous to some M-type asteroids including Psyche, and use a parameterized thermal model to predict a solidification timeline and the resulting chemical profile upon complete solidification. We then explore the potential strength and longevity of a dynamo in the planetesimal's early history. We find that cumulate inner core solidification would be capable of sustaining a dynamo during solidification, but less power would be available for a dynamo in an inward dendritic solidification scenario. We also model and suggest limits on crystal settling and compaction of a possible cumulate inner core. |
Enero de 2016
Source estimate and tsunami forecast from far-field deep-ocean tsunami waveforms – the 27 February 2010 Mw 8.8 Maule earthquake
Authors: M Yoshimoto, S Watada et al
Link: Click here
Abstract
We inverted the 2010 Maule earthquake tsunami waveforms recorded at DART
(Deep-ocean Assessment and Reporting Tsunamis) stations in the Pacific
Ocean by taking into account the effects of the seawater
compressibility, elasticity of the solid earth, and gravitational potential change. |
These effects slow down the tsunami speed and consequently move the slip offshore or updip direction, consistent with the slip distribution obtained by a joint inversion of DART, tide gauge, GPS, and coastal geodetic data. Separate inversions of only near-field DART data and only far-field DART data produce similar slip distributions. The former demonstrates that accurate tsunami arrival times and waveforms of trans-Pacific tsunamis can be forecast in real time. The latter indicates that, if the tsunami source area is as large as the 2010 Maule earthquake, the tsunami source can be accurately estimated from the far-field deep ocean tsunami records without near-field data. |
Enero de 2016
Reconstructing input for artificial neural networks based on embedding theory and mutual information to simulate soil porewater salinity in tidal floodplain
Authors: F Zheng, Y Wan et al
Link: Click here
Abstract
Soil porewater salinity plays an important role in the distribution of
vegetation and biogeochemical processes in coastal floodplain
ecosystems. In this study, artificial neural networks (ANNs) was applied
to simulate the porewater salinity of a tidal floodplain in Florida. We
present an approach based on embedding theory with mutual information
to reconstruct ANN model input time series from one system state
variable. Mutual information between system output and input was computed and the local minimum mutual information points were used to determine a time lag vector for time series embedding and |
reconstruction, with which the mutual information weighted average method was developed to compute the components of reconstructed time series. The optimal embedding dimension was obtained by optimizing model performance. The method was applied to simulate soil porewater salinity dynamics at 12 probe locations in the tidal floodplain influenced by saltwater intrusion using four years (2005 to 2008) data, in which adjacent river water salinity was used to reconstruct model input. The simulated electrical conductivity of the porewater showed close agreement with field observations (RMSE ≤ 0.031 S/m and R2 ≥ 0.897), suggesting the reconstructed input by the proposed approach provided adequate input information for ANN modeling. Multiple linear regression model, partial mutual information algorithm for input variable selection, k-NN algorithm, and simple time delay embedding were also used to further verify the merit of the proposed approach. This article is protected by copyright. All rights reserved. |
Enero de 2016
Gravity increase before the 2015 Mw 7.8 Nepal earthquake
Authors: Shi Chen et al
Link: Click here
Abstract
The 25 April 2015 Nepal earthquake (Mw 7.8) ruptured a segment of the Himalayan front fault zone. Four absolute gravimetric stations in southern Tibet, surveyed from 2010/2011 to 2013 and corrected for secular variations, recorded up to 22.40±1.11μGal/yr of gravity increase during this period. The gravity increase is distinct from
|
the long-wavelength secular trends of gravity decrease over the Tibetan Plateau and may be related to interseismic mass change around the locked plate interface under the Himalayan-Tibetan Plateau. We modeled the source region as a disk of 580km in diameter, which is consistent with the notion that much of the southern Tibetan crust is involved in storing strain energy that drives the Himalayan earthquakes. If validated in other regions, high-precision ground measurements of absolute gravity may provide a useful method for monitoring mass changes in the source regions of potential large earthquakes. |
Enero de 2016
Triggered Tectonic Tremor in Various Types of Fault Systems of Japan Following the 2012 Mw8.6 Sumatra Earthquake
Authors: Kevin Chao et al
Link: Click here
Abstract
Tectonic tremor, an extremely stress-sensitive seismic phenomenon occurring in the brittle-ductile transition section of a fault, is associated with the shearing mechanism of slow slip. Observations of triggered tremor can facilitate the evaluation of the existence of background ambient tremor and slow slip events. This paper presents
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widespread triggered tremor sources in Japan initiated by the surface waves of the 2012 Mw8.6 Sumatra earthquake on strike-slip and thrust faults, in the deep volcanic low-frequency earthquake active area, in the shallow tectonic tremor and very low-frequency earthquake active regions, and in the subduction zone. In most regions, the amplitudes of triggered tremor are generally logarithmically proportional to the dynamic stress caused by various triggering earthquakes. Our observations suggest that triggered tremor in the newly discovered sources is the result of a more rapid rate of background ambient tremor, and evidence has suggested the existence of ambient tremor in some regions. |
Diciembre de 2015
On the magnetic precursor of the Chilean earthquake of February 27, 2010
Authors: N. V. Romanova , V. A. Pilipenko, M. V. Stepanova
Link: Click here
Abstract
Some recent publications reported on an anomalous geomagnetic disturbance that was
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observed three days before the strongest Chilean earthquake on February 27, 2010. The present paper analyzes in detail the data from magnetic station, photometers, and riometers in Canada, Chile, and Antarctica. The analysis unambiguously shows that the supposedly anomalous geomagnetic disturbance was not related to seismic activity and was caused by a standard isolated substorm. |
Diciembre de 2015
Featureless spectra on the Moon as evidence of residual lunar primordial crust
Authors: S. Yamamoto, R. Nakamura et al
Link: Click here
Abstract
We report the global distribution of areas exhibiting no absorption features (featureless or FL) on the lunar surface, based on the reflectance spectral data set obtained by the Spectral Profiler onboard Kaguya/SELENE. We found that FL sites are located in impact basins and large impact craters in the Feldspathic Highlands Terrane (FHT), while there are no FL sites in the Procellarum regions nor the South Pole–Aitken basin. FL sites in each impact basin/crater are |
mainly found at the peak rings or rims, where the purest anorthosite (PAN) sites are also found. At the local scale, most of the FL and PAN points are associated with impact craters and peaks. Most of the FL spectra show a steeper (redder) continuum than the PAN spectra, suggesting the occurrence of space weathering effects. We propose that most of the material exhibiting a FL spectrum originate from space weathered PAN. Taking into account all the occurrence trends of FL sites on the Moon, we propose that both the FL and PAN materials were excavated from the primordial lunar crust during ancient basin formations below the megaregolith in the highlands. Since the FL and PAN sites are widely distributed over the lunar surface, our new data may support the existence of a massive PAN layer below the lunar surface. |
Diciembre de 2015
Does an ionospheric hole appear after an inland earthquake?
Authors: M Kamogawa, T Kanaya et al
Link: Click here
Abstract
Ionospheric disturbances occurred as a result of the tsunami associated with the 2011 M9.0 off the Pacific Coast of the Tohoku earthquake (EQ). The ionospheric disturbances propagated radially from the tsunami source area, termed the traveling ionospheric disturbance. In addition to the traveling ionospheric disturbance, an ionospheric plasma depression lasting for approximately 1 h occurred above the tsunami source area, called a tsunami ionospheric hole. In this study, we compare the ionospheric disturbances caused by large inland and submarine EQs to investigate whether an ionospheric plasma depression only occurs in association with a tsunami. Note that we term an |
EQ with a tsunami a submarine EQ. To investigate the presence of a plasma depression, i.e., an ionospheric hole, associated with an inland EQ, data on total electron content between the global positioning system satellite and its receivers were used. Comparison of two inland and two submarine EQ events with similar magnitudes around 7 showed that ionospheric holes were observed only for the submarine EQs. This discrepancy might be attributed to the different excitation amplitudes of the atmospheric acoustic waves between the unidirectional fault displacement and the tsunami uplift/depression, corresponding to quarter and one-period variations. From this hypothesis, we predicted that an ionospheric hole could be observed after a significantly large inland EQ with a sufficiently large vertical ground displacement. In fact, we recognized the ionospheric hole generated by the large inland EQ that recently occurred in the Nepal with the magnitude of 7.8 on 25 April 2015. |
Diciembre de 2015
Game theory and risk-based leveed river system planning with noncooperation
Authors: R Hui, JR Lund et al
Link: Click here
Abstract
Optimal risk-based levee designs are usually developed for economic
efficiency. However, in river systems containing multiple levees, the
planning and maintenance of different levees are controlled by different
agencies or groups. For example, along many rivers, levees on opposite
riverbanks constitute a simple leveed river system with each levee
designed and controlled separately. Collaborative planning of the two
levees can be economically-optimal for the whole system. Independent and
self-interested landholders on opposite riversides often are willing to
separately determine their individual optimal levee planning, resulting
in a less efficient leveed river system from an overall society-wide
perspective (the tragedy of commons). We apply |
game theory to simple leveed river system planning where landholders on each riverside independently determine their optimal risk-based levee planning. Outcomes from non-cooperative games are analyzed and compared with the overall economically-optimal outcome, which minimizes net flood cost system-wide. The system-wide economically-optimal solution generally transfers residual flood risk to the lower-valued side of the river, but is often impractical without compensating for flood risk transfer to improve outcomes for all individuals involved. Such compensation can be determined and implemented with landholders' agreements on collaboration to develop the economically-optimal planning. By examining iterative multiple-shot non-cooperative games with reversible and irreversible decisions, the costs of myopia for the future in making levee planning decisions show the significance of considering the externalities and evolution path of dynamic water resource problems to improve decision-making. This article is protected by copyright. All rights reserved. |
Diciembre de 2015
Comment on “Can human populations be stabilized?” by Stephen G. Warren
Author: John Colarusso
Link: Click here
Abstract
The article by Warren [2015] presents novel conclusions on demography, challenging the dominant paradigm. What was missing from his analysis was an examination of the social and po litical ramifications that follow from his conclusions.
As Professor Warren points out, our current
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demographic dynamics take place against an abundant and increasing food supply, a supply that surely will have limits. In the dominant paradigm challenged by Warren, the spread of enlightened values, as they are often termed, (see Campbell, Prata and Potts on values) are assumed to lead to a stabilizati on of population, and hence of a sustained adequacy of food supply and a concomitant future where human happiness and dignity are at least within the reach of all (see Lee and Mason). At the present time, although world population is growing, west ill enjoy abundance, except in anomalous conditions of famine or war, so our levels of population are widely viewed as manageable. |
Diciembre de 2015
Low resistivity and permeability in actively deforming shear zones on the San Andreas Fault at SAFOD
Authors: C Morrow, DA Lockner et al
Link: Click here
Abstract
The San Andreas Fault Observatory at Depth (SAFOD) scientific drill hole
near Parkfield, California, crosses the San Andreas Fault at a depth of
2.7 km. Downhole measurements and analysis of core retrieved from Phase 3 drilling reveal two narrow, actively deforming zones of smectite-clay gouge within a roughly 200 m wide fault damage zone of sandstones, siltstones, and mudstones. Here we report electrical resistivity and permeability measurements on core samples from all of these structural units at effective confining pressures up to 120 MPa. Electrical resistivity (~10 Ω-m) and permeability (10−21 to 10−22 m2) in the actively deforming |
zones were 1 to 2 orders of magnitude lower than the surrounding damage zone material, consistent with broader-scale observations from the downhole resistivity and seismic velocity logs. The higher porosity of the clay gouge, 2 to 8 times greater than that in the damage zone rocks, along with surface conduction were the principal factors contributing to the observed low resistivities. The high percentage of fine-grained clay in the deforming zones also greatly reduced permeability to values low enough to create a barrier to fluid flow across the fault. Together, resistivity and permeability data can be used to assess the hydrogeologic characteristics of the fault, key to understanding fault structure and strength. The low resistivities and strength measurements of the SAFOD core are consistent with observations of low resistivity clays that are often found in the principal slip zones of other active faults making resistivity logs a valuable tool for identifying these zones. |
Diciembre de 2015
Air quality forecasting for winter-time PM2.5 episodes occurring in multiple cities in central and southern Chile
Authors:
Pablo E Saide, Marcelo Mena-Carrasco et al
Link: Click here
Abstract
Episodic air quality degradation due to particles occurs in multiple cities in central and southern Chile during the austral winter reaching levels up to 300-800 µg/m3 hourly PM2.5, which can be associated with severe effects on human health. An air quality prediction system is developed to predict such events in near–real-time up to three days in advance for nine cities with regular air quality monitoring: Santiago, Rancagua, Curicó, Talca, Chillan, Los Ángeles, Temuco, Valdivia and Osorno. The system uses the WRF-Chem model configured with a nested 2 km grid-spacing domain to predict weather and inert tracers. The
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tracers are converted to hourly PM2.5 concentrations using an observationally based calibration which is substantially less computationally intensive than a full chemistry model. The conversion takes into account processes occurring in these cities, including higher likelihood of episode occurrence during weekends and during colder days, the latter related to increased wood-burning-stove activity for heating. The system is calibrated and evaluated for April-August 2014 where it has an overall skill of 53-72% of episodes accurately forecasted (61-76% for the best initialization) which is better than persistence for most stations. Forecasts one, two and three days in advance all have skill in forecasting events but often present large variability within them due to different meteorological initializations. The system is being implemented in Chile to assist authority decisions not only to warn the population but also to take contingency-based emission restrictions to try to avoid severe pollution events. |
Diciembre de 2015
Reactivation of Stromboli's summit craters at the end of the 2007 effusive eruption detected by thermal surveys and seismicity
Authors: E Marotta, S Calvari et al
Link: Click here
Abstract
This work arises from the field observations made during the civil protection emergency period connected to the 2007 Stromboli eruption. We observed changes in the shallow feeding system of the volcano to which we give a volcanological interpretation and the relative implications. Here we describe the processes that occurred in the upper feeding system from the end of the 2007 effusive eruption on 3 April to the renewal of the strombolian explosive activity at the summit craters (30 June), interpreted using multidisciplinary data. We used thermal camera data collected both from helicopter and from a fixed station at 400 m to retrieve the evolving summit crater activity. These data, compared with seismic signals and published geochemical records, allowed us to detail the shifting of the degassing activity within the crater terrace from NE to SW, occurred between 15 and 25 April 2007
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prior to the resumption of the strombolian activity. In particular, from mid-April, a gradual SW displacement in the maximum apparent temperatures was recorded at the vents within the summit craters, together with a change in the very long period location and confirmed by variations in geochemical indicators (CO2/SO2 plume ratios and CO2 fluxes) from literature. The shallow feeding system experienced a major readjustment after the end of the effusive activity, determining variations in the pressure leakage of the source, slowly deepening and shifting toward SW. All these data, together with the framework supplied by previous structural surveys, allowed us to propose that the compaction of debris accumulated in the uppermost conduit by inward crater collapses, occurred in early March, produced the observed anomalies. At Stromboli, major morphology changes, taking place in the following years, were anticipated by these small and apparently minor processes occurred in the upper feeding system. Other studies are relating similar changes to modifications of the eruptive activity also at other open-conduit volcanoes, so we believe that it may be important to have a constant monitoring of these phenomena in order to better understand their shallow feeding systems. |
Diciembre de 2015
Geyser eruption intervals and interactions: Examples from El Tatio, Atacama, Chile
Authors: Carolina Muñoz-Saez, A Namiki et al
Link: Click here
Abstract
We compare and contrast data collected in 2012 and 2014 from the El Tatio geyser field, Chile. We identify geyser systems that evolve over time, including changes in the interval between eruptions, development of new thermal features, and interactions between geysers. We study three different cases: (a) an isolated geyser, which is periodic and has nearly identical eruptions every cycle; (b) a geyser and coupled noneruptive pool,
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where the geyser has nonregular cycles and several preplay eruptions before the main eruption; and (c) two geysers and a mud volcano, which have nonregular cycles and are all interacting. Though geysers erupt with different styles, we recognize some common features: the conduit recharges with liquid during the quiescent period, bubbles enter the conduit before eruptions, and eruptions occur when water boils in the upper part of the conduit. The episodic addition of heat may govern the periodicity, while the depth where heat is added dictates the eruption style: conduits with deeper heat input are more likely to show preplay or minor eruptions. The interactions between thermal features can be explained by pressure transmission in subsurface permeable layers between geyser conduits. |
Diciembre de 2015
Time reverse imaging for far-field tsunami forecasting: 2011 Tohoku earthquake case study
Authors: MJ Hossen, PR Cummins et al
Link: Click
Abstract
This paper describes a new method for forecasting far-field tsunamis by combining aspects of least squares tsunami source inversion (LSQ) with time reverse imaging (TRI). This method has the same source representation as LSQ but uses TRI to estimate initial sea surface displacement. We apply this method to the 2011 Japan tsunami, and the results show that the method produces tsunami waveforms of excellent agreement with observed waveforms at both near- and far-field stations not used in the source estimation. The spatial distribution of cumulative sea surface displacement agrees well with other models obtained in more sophisticated inversions, but resolve source kinematics are not well resolved. The method has potential for application in tsunami warning systems, as it is
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computationally efficient and can be used to estimate the initial source model by applying precomputed Green's functions in order to provide more accurate and realistic tsunami predictions. This paper describes a new method for forecasting far-field tsunamis by combining aspects of least squares tsunami source inversion (LSQ) with time reverse imaging (TRI). This method has the same source representation as LSQ but uses TRI to estimate initial sea surface displacement. We apply this method to the 2011 Japan tsunami, and the results show that the method produces tsunami waveforms of excellent agreement with observed waveforms at both near- and far-field stations not used in the source estimation. The spatial distribution of cumulative sea surface displacement agrees well with other models obtained in more sophisticated inversions, but resolve source kinematics are not well resolved. The method has potential for application in tsunami warning systems, as it is computationally efficient and can be used to estimate the initial source model by applying precomputed Green's functions in order to provide more accurate and realistic tsunami predictions. |
Diciembre de 2015
Are there new findings in the search for ULF magnetic precursors to earthquakes?
Authors: F. Masci et al
Link: Click here
Abstract
Moore (1964) in a letter published in Nature reported disturbances in geomagnetic field data prior to the 27 March 1964 Alaska earthquake. After the publication of this report, many papers have shown magnetic changes preceding earthquakes. However, a causal relationship between preearthquake magnetic changes and impending earthquakes has never been demonstrated. As a consequence, after 50 years, magnetic disturbances in the geomagnetic field are still candidate precursory phenomena. Some researchers consider the investigation of ultra low |
frequency (ULF: 0.001–10 Hz) magnetic data the correct approach for identifying precursory signatures of earthquakes. Other researchers, instead, have recently reviewed many published ULF magnetic changes that preceded earthquakes and have shown that these are not actual precursors. The recent studies by Currie and Waters (2014) and Han et al. (2014) aim to provide relevant new findings in the search for ULF magnetic precursory signals. However, in order to contribute to science, alleged precursors must be shown to be valid and reproducible by objective testing. Here we will briefly discuss the state of the art in the search for ULF magnetic precursors, paying special attention to the recent findings of Currie and Waters (2014) and Han et al. (2014). We do not see in these two reports significant evidence that may support the observation of precursory signatures of earthquakes in ULF magnetic records. |
Diciembre de 2015
Geochemistry, thermal evolution, and cryovolcanism on Ceres with a muddy ice mantle
Authors: Marc Neveu et al
Link: Click here
Abstract
We present a model of the internal evolution of Ceres consistent with pre-Dawn observations and preliminary data returned by Dawn. We assume that Ceres accreted ice and both micron- and millimeter-sized rock particles and that micron-sized fines stayed suspended in liquid during differentiation. We conclude that aqueously altered grains were emplaced on Ceres's surface |
during the first tens of megayears of its evolution. Our geochemical simulations suggest that Ceres's unusual surface mineralogy is consistent with aqueous alteration of CM material, possibly by NH3-bearing fluid. Thermal evolution simulations including insulating fines yield present-day liquid at depth if Ceres has a small core or no core at all; otherwise, they yield temperatures at the core-mantle boundary of 240–250 K, just warm enough for chloride brines to persist and be freezing today. We hypothesize that ongoing freezing may overpressurize liquid or briny reservoirs, driving cryovolcanic outflow whose surface expression may have been observed by Dawn at Ceres's “bright spots.” These outflows may contribute to the water vapor being produced at Ceres |
Diciembre de 2015
Gravity increase before the 2015 Mw7.8 Nepal earthquake
Authors: S Chen, M Liu et al
Link: Click here
Abstract
The 25 April 2015 Nepal earthquake (Mw 7.8) ruptured a segment of the Himalayan front fault zone. Four absolute gravimetric stations in southern Tibet, surveyed from 2010/2011 to 2013 and corrected for secular variations, recorded up to 22.40±1.11 μGal/yr of gravity increase during |
this period. The gravity increase is distinct from the long-wavelength secular trends of gravity decrease over the Tibetan Plateau, and may be related to interseismic mass change around the locked plate interface under the Himalayan-Tibetan Plateau. We modeled the source region as a disk of 580 km in diameter, which is consistent with the notion that much of the southern Tibetan crust is involved in storing strain energy that drives the Himalayan earthquakes. If validated in other regions, high-precision ground measurements of absolute gravity may provide a useful method for monitoring mass changes in the source regions of potential large earthquakes. |
Diciembre de 2015
Core solidification and dynamo evolution in a mantle-stripped planetesimal
Authors: A Scheinberg, LT Elkins-Tanton et al
Link: Click here
Abstract
The physical processes active during the crystallization of a
low-pressure, low-gravity planetesimal core are poorly understood but
have implications for asteroidal magnetic fields and large-scale
asteroidal structure. We consider a core with only a thin silicate
shell, which could be |
analogous to some M-type asteroids including Psyche, and use a parameterized thermal model to predict a solidification timeline and the resulting chemical profile upon complete solidification. We then explore the potential strength and longevity of a dynamo in the planetesimal's early history. We find that cumulate inner core solidification would be capable of sustaining a dynamo during solidification, but less power would be available for a dynamo in an inward dendritic solidification scenario. We also model and suggest limits on crystal settling and compaction of a possible cumulate inner core. |
Diciembre de 2015
Smartphones serán usados para crear sistema de alerta temprana de sismos
El proyecto es una colaboración entre investigadores del Servicio Geológico de los Estados Unidos (USGS) y el Centro Sismológico Nacional (CSN) de la Facultad de Ciencias Físicas y Matemáticas de la Universidad de Chile, y contempla la instalación de una red sismológica de baja complejidad y costo, compuesta por 300 teléfonos celulares, de los cuales nueve están en proceso de instalación.
Fuente: Comunicaciones Centro Sismológico Nacional de la Universidad de Chile
Dispositivos comunes de consumo, como los teléfonos inteligentes contienen versiones de bajo costo de los sensores utilizados en la detección de sismos, como GPS y acelerómetros. Estos aparatos si bien son menos precisos que los instrumentos científicos están presentes alrededor del mundo y de forma masiva en muchos lugares. Esa masividad será lo que en un futuro próximo podría permitir desarrollar un sistema de alerta temprana de sismos, que le permitiría a las personas enterarse que viene un terremoto algunos segundos antes que llegue la sacudida lo que da la oportunidad de moverse a un lugar seguro.
La primera parte de este proyecto conjunto se realizará a través de pruebas con una red de 300 aparatos instalada en Chile. Esta semana Benjamin Brooks y Thom Ericksen del USGS, visitaron nuestro país para, junto a Juan Carlos Báez y Rodrigo Sánchez del CSN, instalar los primeros nueve smartphones; dos de ellos fueron puestos en Santiago (RM), otros en Valparaíso (V región), Los Vilos, Salamanca, Combarbalá y Canela baja (IV región), y en los próximos días se instalará otro en Rocas de Santo Domingo (V región) y Navidad (VI región).
Esta red de celulares permitirá monitorear los datos con la finalidad de analizarlos y encontrar un algoritmo que sea apropiado para saber cuándo emitir la alerta. Se estima que el sistema sería efectivo para sismos de magnitud 7 ó superior.
En una segunda etapa del proyecto se espera que el sistema sea colaborativo (a través del llamado crowdsourcing), donde cada persona pueda descargar una aplicación para que su smartphone sea un aparato más de una red masiva.
¿Cómo funciona el sistema?
Benjamin Brooks explica que “el objetivo del proyecto es tener un sistema que detecte un sismo lo más rápido posible para poder enviar una alerta a quienes estén en los alrededores del epicentro, y nos dimos cuenta de que podemos utilizar una tecnología que ya está en todos lados, porque los smartphones pueden servir para dar una alerta temprana”. El investigador del USGS agrega que “la tecnología GPS científica (GNSS) mide los desplazamientos (movimiento) que hay cuando ocurre un terremoto, con los celulares se puede hacer lo mismo, sin embargo su información no es tan precisa lo que sería un problema si tuviéramos una red pequeña, pero si tenemos muchos aparatos, el margen de error disminuye y esto es posible por el bajo costo de los Smartphone en comparación con los instrumentos científicos y en este proyecto buscamos rapidez no precisión”.
Respecto de por qué realizar este proyecto en nuestro país, Brooks explica que “Chile tiene terremotos bastante fuertes y de forma frecuente, en otras partes del mundo para probar este sistema tendríamos que esperar mucho tiempo antes de tener un terremoto mayor a 7, como en la falla de San Andrés (California, EE.UU) donde ocurren cada 300 años. Además, tiene una población bastante educada sobre los terremotos y prestan atención porque les importa y tienen ganas de colaborar. También porque Chile tiene un sistema bastante avanzado en sismología hecho por el CSN, lo que nos permite probar esto en un proyecto conjunto”.
La red de estaciones que se está instalando está compuesta por un prototipo integrado por un Smathphone conectado a internet y a una fuente de poder, al que se le añadió un dispositivo adicional con un segundo chip que entrega datos de posición (GPS) más precisos.
“Este sistema no remplazaría a la red sismológica actual, ya que los datos no son tan precisos, pero ofrece una primera medición rápida, la cual permite dar una alerta ante un gran sismo”, indica Juan Carlos Báez, jefe de Geodesia del CSN.
Brooks agrega que por su bajo costo “puede ser una buena opción en lugares hasta como Nepal donde hay sismos importantes pero no hay financiamiento para una red sismológica robusta”.
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Diciembre de 2015
The ionospheric responses to the 2011 Tohoku, 2012 Haida Gwaii, and 2010 Chile tsunamis: Effects of tsunami orientation and observation geometry
Authors: MA Grawe et al
Link: Click here
Abstract
We show the ionospheric signatures of the 28 October 2012 Haida Gwaii
tsunami in both the total electron content (TEC) and the airglow layer.
In addition, previously reported ionospheric |
signatures from the 11 March 2011 Tohoku and 27 February 2010 Chile tsunamis are reexplored in comparison to the newer Haida Gwaii detections. These events provide excellent test cases in the study of tsunami-ionospheric coupling efficiency, which is most notably affected by the observation geometry, tsunami propagation direction, and background ionospheric density. A simple calculation is developed that incorporates observation geometry to predict the relative coupling efficiency. The predictions are compared to the TEC observations and limitations are discussed. |
Diciembre de 2015
A Global Electric Circuit Model within a Community Climate Model
Authors: GM Lucas, AJG Baumgaertner et al
Link: Click here
Abstract
To determine the complex dependencies of currents and electric fields
within the Global Electric Circuit (GEC) on the underlying physics of
the atmosphere, a new modeling framework of the GEC has been developed
for use within global circulation models. Specifically, the Community
Earth System Modeling (CESM) framework has been utilized. A formulation
of atmospheric conductivity based on ion production and loss mechanisms
(including galactic cosmic rays, radon, clouds and aerosols), conduction
current sources, and ionospheric potential changes due to the influence
of external current systems are |
included. This paper presents a full description of the calculation of the electric fields and currents within the model, which now includes several advancements to GEC modeling as it incorporates many processes calculated individually in previous articles into a consistent modeling framework. This framework uniquely incorporates effects from the troposphere up to the ionosphere within a single GEC model. The incorporation of a magnetospheric potential, which is generated by a separate magnetospheric current system, acts to modulate or enhance the surface level electric fields at high latitude locations. This produces a distinct phasing signature with the GEC potential that is shown to depend on the observation location around the globe. Lastly, the model output for Vostok and Concordia, two high latitude locations, is shown to agree with the observational data obtained at these sites over the same time period. |
Diciembre de 2015
Does an ionospheric hole appear after an inland earthquake?
Authors: M Kamogawa, T Kanaya et al
Link: Click here
Abstract
Ionospheric disturbances occurred as a result of the tsunami associated with the 2011 M9.0 off the Pacific Coast of the Tohoku earthquake (EQ). The ionospheric disturbances propagated radially from the tsunami source area, termed the traveling ionospheric disturbance. In addition to the traveling ionospheric disturbance, an ionospheric plasma depression lasting for approximately 1 h occurred above the tsunami source area, called a tsunami ionospheric hole. In this study, we compare the ionospheric disturbances caused by large inland and submarine EQs to investigate whether an ionospheric plasma depression only occurs in |
association with a tsunami. Note that we term an EQ with a tsunami a submarine EQ. To investigate the presence of a plasma depression, i.e., an ionospheric hole, associated with an inland EQ, data on total electron content between the global positioning system satellite and its receivers were used. Comparison of two inland and two submarine EQ events with similar magnitudes around 7 showed that ionospheric holes were observed only for the submarine EQs. This discrepancy might be attributed to the different excitation amplitudes of the atmospheric acoustic waves between the unidirectional fault displacement and the tsunami uplift/depression, corresponding to quarter and one-period variations. From this hypothesis, we predicted that an ionospheric hole could be observed after a significantly large inland EQ with a sufficiently large vertical ground displacement. In fact, we recognized the ionospheric hole generated by the large inland EQ that recently occurred in the Nepal with the magnitude of 7.8 on 25 April 2015. |
Diciembre de 2015
Seismic hydraulic fracture migration originated by successive deep magma pulses: The 2011–2013 seismic series associated to the volcanic activity of El Hierro Island
Authors: A Díaz-Moreno, JM Ibañez et al
Link: Click here
Abstract
In this manuscript we present a new interpretation of the seismic series
that accompanied eruptive activity off the coast of El Hierro, Canary
Islands, during 2011–2013. We estimated temporal variations of the Gutenberg-Richter b value throughout the period of analysis, and performed high-precision relocations of the preeruptive and syneruptive seismicity using a realistic 3-D velocity model. Our results suggest that eruptive activity and the accompanying seismicity were caused by repeated injections of magma from the mantle into the lower crust. These magma pulses occurred within a small and well-defined volume resulting in the emplacement of fresh magma along the crust-mantle boundary underneath El |
Hierro. We analyzed the distribution of earthquake hypocenters in time and space in order to assess seismic diffusivity in the lower crust. Our results suggest that very high earthquake rates underneath El Hierro represent the response of a stable lower crust to stress perturbations with pulsatory character, linked to the injection of magma from the mantle. Magma input from depth caused large stress perturbations to propagate into the lower crust generating energetic seismic swarms. The absence of any preferential alignment in the spatial pattern of seismicity reinforces our hypothesis that stress perturbation and related seismicity, had diffusive character. We conclude that the temporal and spatial evolution of seismicity was neither tracking the path of magma migration nor it defines the boundaries of magma storage volumes such as a midcrustal sill. Our conceptual model considers pulsatory magma injection from the upper mantle and its propagation along the Moho. We suggest, within this framework, that the spatial and temporal distributions of earthquake hypocenters reflect hydraulic fracturing processes associated with stress propagation due to magma movement. |
Diciembre de 2015
A new interpretation of seismic tomography in the southern Dead Sea basin using neural network clustering techniques
Authors: B Braeuer et al
Link: Click here
Abstract
The Dead Sea is a prime location to study the structure and development of pull-apart basins. We analyzed tomographic models of Vp, Vs, and Vp/Vs using self-organizing map clustering techniques. The method allows us to identify major lithologies by their petrophysical signatures. Remapping the clusters into the subsurface reveals the distribution of basin |
sediments, prebasin sedimentary rocks, and crystalline basement. The Dead Sea basin shows an asymmetric structure with thickness variation from 5 km in the west to 13 km in the east. Most importantly, we identified a distinct, well-defined body under the eastern part of the basin down to 18 km depth. Considering its geometry and petrophysical signature, this unit is interpreted as a buried counterpart of the shallow prebasin sediments encountered outside of the basin and not as crystalline basement. The seismicity distribution supports our results, where events are concentrated along boundaries of the basin and the deep prebasin sedimentary body. Our results suggest that the Dead Sea basin is about 4 km deeper than assumed from previous studies. |
Diciembre de 2015
Disruption of groundwater systems by earthquakes
Authors: X Liao, CY Wang et al
Link: Click here
Abstract
Earthquakes are known to enhance permeability at great distances, and
this phenomenon may also disrupt groundwater systems by breaching the
barrier between different reservoirs. Here we analyze the tidal response
of water level in a deep (~4 km) well before and after the 2008 M7.9 Wenchuan earthquake to show that the earthquake not only changed the permeability but |
also altered the poroelastic properties of the groundwater system. Based on lithologic well logs and experimental data for rock properties, we interpret the change to reflect a coseismic breaching of aquitards bounding the aquifer, due perhaps to clearing of preexisting cracks and creation of new cracks, to depths of several kilometers. This may cause mixing of groundwater from previously isolated reservoirs and impact the safety of groundwater supplies and underground waste repositories. The method demonstrated here may hold promise for monitoring aquitard breaching by both natural and anthropogenic processes. |
Seisms Forecast & Prediction
1) Research Gate
2) Google Scholar: Earthquake Forecasting and Earthquake Prediction: Different Approaches for Obtaining the Best Model
3) Geoscience World |
Noviembre de 2015
Acoustically-induced slip in sheared granular layers: application to dynamic earthquake triggering
Authors: B Ferdowsi, M Griffa et al
Link: Click here
Abstract
A fundamental mystery in earthquake physics is how can an earthquake be triggered by distant seismic sources? Here, we use discrete element method simulations of a granular layer, during stick-slip, that is subject to transient vibrational excitation to gain further insight into the physics of dynamic earthquake triggering. Using Coulomb friction law for grains interaction, we observe delayed triggering of slip in the granular gouge. |
We find that at a critical vibrational amplitude (strain) there is an abrupt transition from negligible time-advanced slip (clock advance) to full clock advance, i.e., transient vibration and triggered slip are simultaneous. The critical strain is order of 10-6, similar to observations in the laboratory and in Earth. The transition is related to frictional weakening of the granular layer due to a dramatic decrease in coordination number and the weakening of the contact force network. Associated with this frictional weakening is a pronounced decrease in the elastic modulus of the layer. The study has important implications for mechanisms of triggered earthquakes and induced seismic events and points out the underlying processes in response of the fault gouge to dynamic transient stresses. |
Noviembre de 2015
Evidence for primordial water in Earth’s deep mantle
Authors:
Lydia J. Hallis, Gary R. Huss et al
Link: Click here
Abstract
The hydrogen-isotope [deuterium/hydrogen (D/H)] ratio of Earth can be used to constrain the origin of its water. However, the most accessible reservoir, Earth’s oceans, may no longer represent the original (primordial) D/H ratio, owing to changes caused by water cycling between the surface and the interior. Thus, a reservoir completely isolated from surface processes is required to define Earth’s original D/H signature. Here we present data for Baffin Island and Icelandic lavas, which suggest that the deep mantle has a low D/H ratio (δD more negative than –218 per mil). Such
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strongly negative values indicate the existence of a component within Earth’s interior that inherited its D/H ratio directly from the protosolar nebula. The hydrogen-isotope [deuterium/hydrogen (D/H)] ratio of Earth can be used to constrain the origin of its water. However, the most accessible reservoir, Earth’s oceans, may no longer represent the original (primordial) D/H ratio, owing to changes caused by water cycling between the surface and the interior. Thus, a reservoir completely isolated from surface processes is required to define Earth’s original D/H signature. Here we present data for Baffin Island and Icelandic lavas, which suggest that the deep mantle has a low D/H ratio (δD more negative than –218 per mil). Such strongly negative values indicate the existence of a component within Earth’s interior that inherited its D/H ratio directly from the protosolar nebula.
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Noviembre de 2015
On magnetic estimation of Earth's core angular momentum variation
Authors: S Asari et al
Link: Click here
Abstract
We study systematically the estimation of Earth's core angular momentum (CAM) variation between 1962.0 and 2008.0 by using core surface flow models derived from the recent geomagnetic field model C3FM2. Various flow models are derived by changing four parameters that control the least squares flow inversion. The parameters include the spherical harmonic (SH) truncation degree of the flow models and two Lagrange multipliers that control the weights of two additional constraints. The first constraint forces the energy spectrum of the flow solution to follow a power law, where l is the SH degree and p is the fourth parameter. The second allows to modulate the solution continuously between the dynamical states of
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tangential geostrophy (TG) and tangential magnetostrophy (TM). The calculated CAM variations are examined in reference to twofeatures of the observed length-of-day (LOD) variation, namely, its secular trend and 6 year oscillation. We find flow models in either TG or TM state for which the estimated CAM trends agree with the LOD trend. It is necessary for TM models to have their flows dominate at planetary scales, whereas TG models should not be of this scale; otherwise, their CAM trends are too steep. These two distinct types of flow model appear to correspond to the separate regimes of previous numerical dynamos that are thought to be applicable to the Earth's core. The phase of the subdecadal CAM variation is coherently determined from flow models obtained with extensively varying inversion settings. Multiple sources of model ambiguity need to be allowed for in discussing whether these phase estimates properly represent that of Earth's CAM as an origin of the observed 6 year LOD oscillation. |
Noviembre de 2015
Insights on earthquake triggering processes from early aftershocks of repeating microearthquakes
Authors: O Lengliné et al
Link: Click here
Abstract
Characterizing the evolution of seismicity rate of early aftershocks can yield important information about earthquake nucleation and triggering. However, this task is challenging because early aftershock seismic signals are obscured by those of the mainshock. Previous studies of early aftershocks employed high-pass filtering and template matching but had limited performance and completeness at very short times. Here we take advantage of repeating events previously identified on the San Andreas Fault at Parkfield and apply empirical Green's function deconvolution techniques. Both Landweber and sparse deconvolution methods reveal the occurrence of aftershocks as early as
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few tenths of a second after the mainshock. These events occur close to their mainshock, within one to two rupture lengths away. The aftershock rate derived from this enhanced catalog is consistent with Omori's law, with no flattening of the aftershock rate down to the shortest resolvable timescale ∼0.3 s. The early aftershock rate decay determined here matches seamlessly the decay at later times derived from the original earthquake catalog, yielding a continuous aftershock decay over timescales spanning nearly 8 orders of magnitude. Aftershocks of repeating microearthquakes may hence be governed by the same mechanisms from the earliest time resolved here, up to the end of the aftershock sequence. Our results suggest that these early aftershocks are triggered by relatively large stress perturbations, possibly induced by aseismic afterslip with very short characteristic time. Consistent with previous observations on bimaterial faults, the relative location of early aftershocks shows asymmetry along strike, persistent over long periods. |
Noviembre de 2015
A new interpretation of seismic tomography in the southern Dead Sea basin using neural network clustering techniques
Authors: B Braeuer et al
Link: Click here
Abstract
The Dead Sea is a prime location to study the structure and development of pull-apart basins. We analyzed tomographic models of Vp, Vs and Vp/Vs using self-organizing map clustering techniques. The method allows us to identify major lithologies by their petrophysical signatures. Re-mapping the clusters into the subsurface reveals the distribution of basin
|
sediments, pre-basin sedimentary rocks and crystalline basement. The Dead Sea basin shows an asymmetric structure with thickness variation from 5 km in the west to 13 km in the east. Most importantly, we identified a distinct, well-defined body under the eastern part of the basin down to 18 km depth. Considering its geometry and petrophysical signature, this unit is interpreted as a buried counterpart of the shallow pre-basin sediments encountered outside of the basin, and not as crystalline basement. The seismicity distribution supports our results, where events are concentrated along boundaries of the basin and the deep pre-basin sedimentary body. Our results suggest, that the Dead Sea basin is about 4 km deeper than assumed from previous studies. |
Noviembre de 2015
Disruption of groundwater systems by earthquakes
Authors: X Liao, CY Wang et al
Link: Click here
Abstract
Earthquakes are known to enhance permeability at great distances
and this phenomenon may also disrupt groundwater systems by
breaching the barrier between different reservoirs. Here we
analyze the tidal response of water level in a deep (~4 km)
well before and after the 2008 M7.9 Wenchuan earthquake to
show that the earthquake not only changed the permeability
but
|
also
altered the poroelastic properties of the groundwater system.
Based on lithologic well logs and experimental data for rock
properties we interpret the change to reflect a coseismic breaching
of aquitards bounding the aquifer, due perhaps to clearing of
pre-existing cracks and creation of new cracks, to depths of
several km. This may cause mixing of groundwater from previously
isolated reservoirs and impact the safety of groundwater supplies
and underground waste repositories. The method demonstrated
here may hold promise for monitoring aquitard breaching by both
natural and anthropogenic processes. |
Noviembre de 2015
Deterministic model of earthquake clustering shows reduced
stress drops for nearby aftershocks
Authors: Bruce E. Shaw, Keith Richards-Dinger et
al
Link: Click here
Abstract
While a number of viable physical mechanisms have been offered
to explain the temporal clustering of aftershocks, the spatial
clustering of aftershocks, in particular the concentrated
productivity of aftershocks very near the mainshock rupture
area, has been difficult to
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reproduce
with physical models. Here we present a new deterministic physical
model capable of reproducing both the spatial and temporal clustering.
We apply this new model to a longstanding puzzling question
raised by ground motion observations, which suggest that nearby
aftershocks show reduced ground motions relative to similar
magnitude mainshocks. In the model, the physical basis for these
observations is reduced stress drops for nearby aftershocks
compared to similar magnitude mainshocks. These reduced stress
drops are due to nearby aftershocks rerupturing incompletely
healed parts of the fault which ruptured in the mainshock. |
Octubre de 2015
Hydrothermal response to a volcano-tectonic earthquake
swarm, Lassen, California
Authors: S. E. Ingebritsen, D. R. Shelly et al
Link: Click here
Abstract
The increasing capability of seismic, geodetic, and hydrothermal
observation networks allows recognition of volcanic unrest
that could previously have gone undetected, creating an imperative
to diagnose and interpret unrest episodes. A November 2014
earthquake swarm near Lassen Volcanic National Park, California,
which included the largest earthquake in the area in more
than
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60?years,
was accompanied by a rarely observed outburst of hydrothermal
fluids. Although the earthquake swarm likely reflects upward
migration of endogenous H2O-CO2 fluids in the source region,
there is no evidence that such fluids emerged at the surface.
Instead, shaking from the modest sized (moment magnitude 3.85)
but proximal earthquake caused near-vent permeability increases
that triggered increased outflow of hydrothermal fluids already
present and equilibrated in a local hydrothermal aquifer. Long-term,
multiparametric monitoring at Lassen and other well-instrumented
volcanoes enhances interpretation of unrest and can provide
a basis for detailed physical modeling. |
Octubre de 2015
Internal structure of the Moon inferred from Apollo seismic
data and selenodetic data from GRAIL and LLR
Authors: K Matsumoto, R Yamada et al
Link: Click here
Abstract
The internal structure of the Moon is important for discussions
on its origin and evolution. However, the deep structure of
the Moon is still debated due to the absence of comprehensive
seismic data. This study explores lunar interior models by
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complementing
Apollo seismic travel time data with selenodetic data which
have recently been improved by Gravity Recovery and Interior
Laboratory (GRAIL) and Lunar Laser Ranging (LLR). The observed
data can be explained by models including a deep-seated zone
with a low velocity (S wave velocity = 2.9 ± 0.5 km/s)
and a low viscosity (~3 × 1016 Pa s). The thickness of
this zone above the core-mantle boundary is larger than 170
km, showing a negative correlation with the radius of the fluid
outer core. The inferred density of the lowermost mantle suggests
a high TiO2 content (>11 wt.%) which prefers a mantle overturn
scenario. |
Octubre de 2015
Possible seasonality in large deep-focus earthquakes
Authors: Z Zhan et al
Link: Click here
Abstract
Large deep-focus earthquakes (magnitude > 7.0, depth >
500 km) have exhibited strong seasonality in their occurrence
times since the beginning of global earthquake catalogs. Of
60 such events from 1900 to the present, 42 have occurred
in the middle half of each year. The seasonality appears strongest
in the northwest Pacific subduction zones and
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weakest
in the Tonga region. Taken at face value, the surplus of northern
hemisphere summer events is statistically significant, but due
to the ex post facto hypothesis testing, the absence of seasonality
in smaller deep earthquakes, and the lack of a known physical
triggering mechanism, we cannot rule out that the observed seasonality
is just random chance. However, we can make a testable prediction
of seasonality in future large deep-focus earthquakes, which,
given likely earthquake occurrence rates, should be verified
or falsified within a few decades. If confirmed, deep earthquake
seasonality would challenge our current understanding of deep
earthquakes. |
Octubre de 2015
Experimental evidence of electrification processes during
the 2009 L'Aquila earthquake main shock
Author: P. Nenovski
Link: Click here
Abstract
Two types of coseismic magnetic field events are simultaneously
observed: transient offset events and magnetic field signal
that occurred at the destructive, Mw6.1 L'Aquila earthquake
main
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shock.
The offset event, conventionally interpreted as a signature
of piezomagnetic effects, however, could not be explained as
such. In the second type of coseismic event, the transient magnetic
signal starts simultaneously with the offset event and reaches
amplitude of 0.8?nT in the total magnetic field. The signal
is a local one; its amplitude shape resembles diffusion-like
form with time scale characteristics that are indicative for
a source deep in the crust. The polarity of the transient signal
is in the horizontal plane and nearly parallel to the L'Aquila
fault strike. |
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