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Mayo de 2021
Sensitivity of permeability changes to different earthquakes in a fault zone: Possible evidence of dependence on the frequency of seismic waves
Authors: Xin Liao, Yun Shi et al.
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Changes in the permeability of a fault zone are dependent upon the frequency of seismic waves, and is an important phenomenon whose mechanisms have not be completely elucidated to date. In this study, the tidal response of water level

in well Chuan06 was considered as an indicator of the permeability of the fault zone, and the sensitivity of permeability changes to earthquakes with different epicentral distances were investigated. The results suggested that the permeability change induced by seismic waves is frequency dependent. In addition, based on the mechanisms of permeability changes induced by the seismic waves, the difference in sensitivity may be attributed to the different sizes of the fractures in the fault zone. These findings are likely to contribute to an understanding of hydrogeological responses and seismic activity induced by the earthquakes.

Mayo de 2021
A Decade of Lessons Learned from the 2011 Tohoku oki Earthquake
Authors: N. Uchida and R. Bürgmann.
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The 2011 Mw 9.0 Tohoku oki earthquake is one of the world’s best recorded ruptures. In the aftermath of this devastating event, it is important to learn from the complete record. We describe the state of knowledge of the megathrust earthquake generation process before the earthquake, and what has been learned in the decade since the historic event. Prior to 2011, there were a number of studies suggesting the potential of a great megathrust earthquake in NE Japan from geodesy, geology, seismology, geomorphology, and paleoseismology, but results from each field were not enough to enable a consensus assessment of the hazard. A transient unfastening of interplate coupling and increased .

seismicity were recognized before the earthquake, but did not lead to alerts. Since the mainshock, follow up studies have (1) documented that the rupture occurred in an area with a large interplate slip deficit, (2) established large near‐trench coseismic slip, (3) examined structural anomalies and fault zone materials correlated with the coseismic slip, (4) clarified the historical and paleoseismic recurrence of M 9 earthquakes, and (5) identified various kinds of possible precursors. The studies have also illuminated the heterogeneous distribution of coseismic rupture, aftershocks, slow earthquakes and aseismic afterslip, and the enduring viscoelastic response, which together make up the complex megathrust earthquake cycle. Given these scientific advances, the enhanced seismic hazard of an impending great earthquake can now be more accurately established, although we do not believe such an event could be predicted with confidence

Mayo de 2021
Relationship Between Subduction Erosion and the Up Dip Limit of the 2014 Mw 8.1 Iquique Earthquake
Authors: Florian Petersen, Dietrich Lange et al.
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The aftershock distribution of the 2014 Mw 8.1 Iquique earthquake offshore northern Chile, identified from a long term deployment of ocean bottom seismometers installed eight months after the mainshock, in conjunction with seismic reflection imaging, provides insights into the processes regulating the updip limit of coseismic

rupture propagation. Aftershocks updip of the mainshock hypocenter frequently occur in the upper plate and are associated with normal faults identified from seismic reflection data. We propose that aftershock seismicity near the plate boundary documents subduction erosion that removes mass from the base of the wedge and results in normal faulting in the upper plate. The combination of very little or no sediment accretion and subduction erosion over millions of years has resulted in a very weak and aseismic frontal wedge. Our observations thus link the shallow subduction zone seismicity to subduction erosion processes that control the evolution of the overriding plate.

Mayo de 2021
Solar or Diesel: A Comparison of Costs for Groundwater Fed Irrigation in Sub Saharan Africa Under Two Energy Solutions
Authors:Hua Xie, Claudia Ringler et al.
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Sub Saharan Africa has long been beset with food insecurity and energy poverty. Expanding irrigated agriculture can help boost food production in the region, but this requires energy for accessing water, especially in groundwater fed irrigation. This paper compared economic performance of groundwater

pumping for irrigation under two energy solutions: solar photovoltaic (PV) and diesel fuel. We estimated the life cycle costs of the power units of two pumping systems for a range of crop and irrigation method scenarios and mapped their relative cost effectiveness over cropland in sub Saharan Africa. As a renewable and clean energy source, solar energy has attracted much attention and there is keen interest in investing in solar PV to support the development of irrigated agriculture. Results of this study provide insights into the prospects of promoting solar irrigation in sub Saharan Africa.

Abril de 2021
Flexural Control of Basal Crevasse Opening Under Ice Shelves
Authors: W. Roger Buck and Ching Yao Lai
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Classical analyses of basal crevasse opening do not account for the free surface of a floating ice layer. We describe a high resolution numerical treatment of the opening of a single crevasse in a finite thickness elastic layer floating on an inviscid substrate. For low extensional stress (less than about half of the expected maximum for a freely

floating shelf) the resulting crevasse height and width match previous studies. For larger magnitude applied extensional stresses, the new results predict basal crevasse widths an order of magnitude greater than the classical solution. An analysis using the thin layer approximation shows that the greatly increased predicted width of basal crevasse opening results from layer bending. Given that the height and width of basal crevasses are non linear functions of the stress experienced by an ice shelf, the new model results may enable better estimation of buttressing stresses for different parts of ice shelves.

Abril de 2021
Seismological Structures on Bimodal Distribution of Deep Tectonic Tremor
Authors: Yasunori Sawaki, Yoshihiro Ito et al.
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Deep tectonic tremors occur at the downdip extent of the seismogenic zone due to fluid processes. Beneath the northeastern Kii Peninsula, southwestern Japan, there is an along‐dip bimodal distribution of tremor. However, no constraint exists on the structures controlling that distribution. We extract detailed seismological structures from multi band receiver functions and evaluate conditional

differences in the distribution. To achieve high resolution images along the plate interface, we utilize records of regional deep focus earthquakes from the Pacific slab. Cross section images show the subducting oceanic plate with depth‐dependent phases along the bimodal distribution, revealing a conspicuous plate interface at the updip portion and an inconspicuous interface below the mantle wedge at the downdip portion. This indicates that episodic tremors occur in the high pore‐fluid plate interface below the impermeable forearc crust, and that continual tremors occur at the permeable mantle wedge corner, owing to continuous fluid supply from the oceanic crust.

Abril de 2021
A risk-based approach for managing hydraulic fracturing–induced seismicity
Authors: Ryan Schultz, Gregory C. Beroza et al.
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Risks from induced earthquakes are a growing concern that needs effective management. For hydraulic fracturing of the Eagle Ford shale in southern Texas, we developed a risk-informed strategy for choosing red-light thresholds that require immediate well shut-in. We used a combination of datasets to simulate spatially

heterogeneous nuisance and damage impacts. Simulated impacts are greater in the northeast of the play and smaller in the southwest. This heterogeneity is driven by concentrations of population density. Spatially varying red-light thresholds normalized on these impacts [moment magnitude (Mw) 2.0 to 5.0] are fairer and safer than a single threshold applied over a broad area. Sensitivity tests indicate that the forecast maximum magnitude is the most influential parameter. Our method provides a guideline for traffic light protocols and managing induced seismicity risks.

Abril de 2021
Diachronous Growth of the Northern Tibetan Plateau Derived From Flexural Modeling
Authors: Lin Wang, Feng Cheng et al.
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The early Cenozoic topography of the northern Tibetan plateau remains enigmatic because of the paucity of independent paleoelevation constraints. Long‐held views of northward propagating deformation imply a low Paleogene elevation, but this prediction is speculative. We apply flexural modeling to reconstructed Paleogene isopach data obtained from the Qaidam basin, which requires a

larger topographic load in the Qilian Shan and a smaller load in the Eastern Kunlun Shan. Incorporating knowledge of proto‐Paratethys marine incursions in the Paleogene Qaidam basin, we infer a topographically low (0.4–1.0 km) Eastern Kunlun Shan and a higher (0.4–1.5 km) Qilian Shan during the Paleogene. This implied paleo‐relief contrasts with previous predictions and suggests more recently, Neogene surface uplift in the Eastern Kunlun Shan has been more significant than in Qilian Shan, highlighting diachronous growth of the northern Tibetan plateau. The low moderate paleoelevation implies a warmer and more humid climate in Northern Tibet during the Paleogene.

Abril de 2021
Unraveling the Causes of the Seismicity Induced by Underground Gas Storage at Castor, Spain
Authors:Víctor Vilarrasa, Silvia De Simone et al.
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The offshore Castor Underground Gas Storage (UGS) project had to be halted after gas injection triggered three M4 earthquakes, each larger than any ever induced by UGS. The mechanisms that induced seismicity in the crystalline basement at 5–10 km depth after gas injection at 1.7 km depth remain unknown. Here, we propose a combination of mechanisms to explain the observed seismicity

First, the critically stressed Amposta fault, bounding the storage formation, crept by the superposition of well known overpressure effects and buoyancy of the relatively light injected gas. This aseismic slip brought an unmapped critically stressed fault in the hydraulically disconnected crystalline basement to failure. We attribute the delay between induced earthquakes to the pressure drop associated to expansion of areas where earthquakes slips cause further instabilities. Earthquakes occur only after these pressure drops have dissipated. Understanding triggering mechanisms is key to forecast induced seismicity and successfully design deep underground operations.

Abril de 2021
Analyzing Low Frequency Seismic Events at Cerberus Fossae as Long Period Volcanic Quakes
Authors: Sharon Kedar, Mark P. Panning et al.
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The InSight Mission began acquiring the first seismic data on Mars in early 2019 and has detected hundreds of events. The largest events recorded to date originate at Cerberus Fossae, a young volcanic region characterized by high volume, low viscosity lava flows. A handful of Low Frequency (LF) quakes that share key attributes of Long Period quakes recorded on Earth's volcanoes are also traced to Cerberus Fossae. This study explores whether a traditional volcanic source model that simulates the generation of tremor as pressurized fluid makes its way through a channel at depth, can explain these atypical LF events. We consider a

wide range of physical parameters including fluid viscosity, the ratio of driving pressure to lithostatic pressure, aspect ratio of the channel, and the equilibrium channel opening. We find that the model can produce the observed seismic signature, with a combination of low-viscosity magma and high volume flux of ~104 - 105 m3/s that are within an order-of-magnitude agreement with Cerberus Fossae lava flow properties deduced from analysis of lava flow dimensions. It is impossible, however, at this stage to conclude whether or not this is a likely explanation for Mars, as the model results in fluxes that are extreme for Earth yet are just within bounds of what has been inferred for Cerberus Fossae. We therefore conclude that we cannot rule out active magma flow as the mechanism responsible for the atypical LF events that likely originate from Cerberus Fossae.

Abril de 2021
Seismic Strain Rate and Flexure at the Hawaiian Islands Constrain the Frictional Coefficient
Authors: A. Bellas and S. J. Zhong
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Flexure occurs on intermediate geologic timescales (~1 Myr) due to volcanic-island building at the Island of Hawaii, and the deformational response of the lithosphere is simultaneously elastic, plastic, and ductile. At shallow depths and low temperatures, elastic deformation transitions to frictional failure on faults where stresses exceed a threshold value, and this complex rheology controls the rate of deformation manifested by earthquakes. In this study, we estimate the seismic strain rate based on earthquakes recorded between 1960 and 2019 at Hawaii, and the estimated strain rate with 10-18–10-15 s-1 in magnitude exhibits a local minimum or neutral bending plane at 15 km depth within the

lithosphere. In comparison, flexure and internal deformation of the lithosphere are modeled in 3D viscoelastic loading models where deformation at shallow depths is accommodated by frictional sliding on faults and limited by the frictional coefficient (µf), and at larger depths by low-temperature plasticity and high-temperature creep. Observations of flexure and the seismic strain rate are best-reproduced by models with µf = 0.3 ± 0.1 and modified laboratory-derived low-temperature plasticity. Results also suggest strong lateral variations in the frictional strength of faults beneath Hawaii. Our models predict a radial pattern of compressive stress axes relative to central Hawaii consistent with observations of earthquake pressure (P) axes. We demonstrate that the dip angle of this radial axis is essential to discerning a change in the curvature of flexure, and therefore has implications for constraining lateral variations in lithospheric strength.

Abril de 2021
Global groundwater wells at risk of running dry
AuthorsScott Jasechko and Debra Perrone
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Groundwater wells supply water to billions of people, but they can run dry when water tables decline. Here, we analyzed construction records for ~39 million globally distributed wells. We show that 6 to 20% of wells are no more than 5 meters deeper than the water table, implying that millions of wells

are at risk of running dry if groundwater levels decline by only a few meters. Further, newer wells are not being constructed deeper than older wells in some of the places experiencing significant groundwater level declines, suggesting that newer wells are at least as likely to run dry as older wells if groundwater levels continue to decline. Poor water quality in deep aquifers and the high costs of well construction limit the effectiveness of tapping deep groundwater to stave off the loss of access to water as wells run dry.

Abril de 2021
First Focal Mechanisms of Marsquakes
Authors: Nienke Brinkman, Simon C. Stähler et al.
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Since February 2019, NASA's InSight lander is recording seismic signals on the planet Mars, which, for the first time, allows to observe ongoing tectonic processes with geophysical methods. A number of Marsquakes have been located in the Cerberus Fossae graben system in Elysium Planitia and further west, in the Orcus Patera depression. We present a first study of the focal mechanisms of three well-recorded events (S0173a, S0183a, S0235b) to determine the processes dominating in the source region. We infer for all three events a predominantly extensional setting. Our method is

adapted to the case of a single, multicomponent receiver and based on fitting waveforms of P and S waves against synthetic seismograms computed for the initial crustal velocity model derived by the InSight team. We explore the uncertainty due to the single-station limitation and find that even data recorded by one station constrains the mechanisms (reasonably) well. For the events in the Cerberus Fossae region (S0173a, S0235b) normal faulting with a relatively steep dipping fault plane is inferred, suggesting an extensional regime mainly oriented E-W to NE-SW. The fault regime in the Orcus Patera region is not determined uniquely because only the P wave can be used for the source inversion. However, we find that the P and weak S waves of the S0183a event show similar polarities to the event S0173, which indicates similar fault regimes.

Abril de 2021
Seismological rockslide warnings in the Himalaya
Authors: N. Purnachandra Rao, Rajesh Rekapalli et al. | Edited by Jennifer Sills | Science Magazine
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On 7 February, a glaciated ridge of Ronti mountain in the western Himalaya faailed at 5600 m above sea level, causing a rocksslide that inducedd a debris flow and flooding in the tributaries of the river Ganga. The events destoyed two hydroelectric projects and claimed more 100 lives. Himalayan countries urgentrly need a robust early warning mechanism for rockslides aand triggered flow cascades such as debris...

Abril de 2021
Bayesian Integration Using Resistivity and Lithology for Improving Estimation of Hydraulic Conductivity
Authors: Shih-Yang Cheng and Kuo-Chin Hsu.
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The characterization of spatially heterogeneous hydraulic conductivity (K) is important in groundwater resources management. We propose a Bayesian statistical method that integrates multiple secondary data (continuous and category data) with primary data (K) to improve regional K field characterization. Considering the disparity of the data scale, spatial scarcity of primary and secondary data, and need for regional scale site characterization, the aquifer thickness is used as the scale for data integration. We transform the high resolution secondary data to the scale of K and perform linear/nonlinear regression analyses for the transformed secondary data and primary data. A Bayesian approach using

Metropolis within Gibbs sampling is developed for jointly integrating the primary and transformed secondary data without a limitation on the type of data attribute and the number of data set. A synthetic example is first presented to demonstrate the capability of the proposed method. Results show that the correlation strength, not the relation type, is the primary factor for improving the estimates. The Bayesian method is applied to Choushui River alluvial fan in Taiwan. Resistivity logs and a lithological description are first upscaled and then simultaneously integrated in the K estimation. Results indicate that the improvement of the K estimate obtained using resistivity data is higher in the proximal and mid fans but lower in the distal fan compared to that obtained using lithofacies data. Jointly integrating two attribute data outperforms using one or no secondary data set for K estimates. The proposed Bayesian integration method is thus versatile and suitable for large scale aquifer characterization.

Abril de 2021
Identification of Surface Deformation in InSAR Using Machine Learning
Authors: Clayton M. J. Brengman and William D. Barnhart
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The availability and frequency of synthetic aperture radar (SAR) imagery are rapidly increasing. This surge of data presents new opportunities to constrain surface deformation that spans various spatial and temporal scales. This expansion also introduces common challenges associated with large volumes of data, including best practices for analyzing these data. In recent years, machine learning techniques have been at the forefront of big data challenges, as an efficient methodology for automatically classifying large volumes of data. Convolutional Neural Networks (CNNs), in particular, have achieved strong levels of performance on image classification problems. Here we present SarNet, a CNN developed to

detect, locate, and classify the presence of co seismic like surface deformation within an interferogram. We trained SarNet using 4 × 106 synthetic interferograms, including both wrapped and unwrapped forward modeled co seismic like surface deformation with synthetic noise representative of the atmospheric and topographic noise found in interferograms. The results show that SarNet obtains an overall accuracy of 99.74% on a validation data set. We use class activation maps (CAMs) to show that SarNet returns the location of surface deformation within the interferogram. We employ a transfer learning method to translate the accuracy of SarNet trained on synthetic data to real interferograms with manually classified co‐seismic surface displacement. We train SarNet on 32 interferograms containing labeled co‐seismic surface deformation as well as noise. The results show that, through transfer learning, SarNet obtains an overall accuracy of 85.22% on a real InSAR data set, and that SarNet returns the location of the surface deformation within the interferogram.

Marzo de 2021
Injection induced seismicity size distribution dependent on shear stress
Authors: Y. Mukuhira, M. C. Fehler et al.
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Frequency magnitude distribution of a series of natural earthquakes and laboratory earthquakes correlates with the applied stress. However, the variation of the frequency magnitude distribution for injection-induced seismicity has not been

understood well since the stress state is rather constant in reservoir scale. This study investigates the stress state of the faults that caused the injection-induced seismicity. We found that the events that occurred from the fault that oriented to have relatively higher shear stress caused the b-value reduction. This finding provides the new perspective of the scaling law of frequency magnitude distribution for induced seismicity. This insight leads to seismic hazard mitigation due to fluid injection.

Marzo de 2021
Using array-derived rotational motion to obtain local wave propagation properties from earthquakes induced by the 2018 geothermal stimulation in Finland
Authors: G. Taylor, G. Hillers et al.
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Earthquakes generate seismic waves consisting of both translational (back and forth) and rotational ground motion. Translational motion is routinely measured by standard seismometers, but the observation of the rotational motion requires relatively expensive and rare instruments. In this study we estimate rotational ground motion caused by earthquakes using groups of translational seismometers. This technique—computing rotational motion from translational

seismometers—has been used before, but the novelty of our study is to use high quality recordings of earthquakes that were induced by the creation of a geothermal reservoir at 6 km depth in bedrock. We use our measurements of ground rotation to estimate the speed and direction in which the seismic waves are travelling when they reach the seismometers. We find that the direction in which the seismic waves travel usually points back to the earthquake location, but at some seismometers the waves arrive from a different direction. At these locations, it is likely that local geological features are altering the direction of the waves. We expect that our findings will provide access to approaches for determining earthquake characteristics and Earth structure that currently require highly specialised instruments.

Marzo de 2021
Investigating a tsunamigenic megathrust earthquake in the Japan Trench
Authors: Shuichi Kodaira, Takeshi Iinuma and Kentaro Imai.
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Ten years ago, the magnitude 9 Tohoku-oki earthquake rocked Japan and caused massive damage. The earthquake also generated a destructive tsunami, the impacts of which are still being managed today. Kodaira et al. review what was learned from the tremendous number of observations from the great earthquake that unexpectedly ruptured into a shallow part of the megathrust fault. Postseismic deformation is ongoing, as is the risk of another very large normal

fault earthquake seaward of the Japan Trench. Ten years have passed since the 2011 Tohoku-oki earthquake occurred in the Japan Trench, where the Pacific plate subducts beneath the continental plate. The earthquake and tsunami caused enormous damage along the coast of northeast Japan in the Tohoku region, and local communities are still recovering. Tsunami traces more than 10 m above sea level were observed along 530 km of coastline in central and northeast Japan, and runups higher than 20 m were observed over about 200 km of the Tohoku coast. The tsunami inundated an area of 561 km2, and its runup reached a maximum of 40 m in northern Tohoku. These statistics made it one of the largest tsunamis ever recorded in historical literature as well as in geological records...

Marzo de 2021
Evidence for the Innermost Inner Core: Robust Parameter Search for Radially Varying Anisotropy Using the Neighborhood Algorithm
Authors: J. Stephenson, H Tkalčić et al
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The model of cylindrical anisotropy in the inner core (IC) states that seismic rays traveling parallel to the Earth's rotational axis travel faster than those parallel to the equator. There have been continuing discrepancies in estimates of the strength and orientation of anisotropy, with some evidence suggesting that such a model may not be supported by available data. Here, we scrutinize the radial dependence of anisotropy within the IC, where the nature of anisotropy has been shown to change anywhere between a 300 and 800 km radius. We

use recent travel time data from the International Seismological Centre in conjunction with the neighborhood algorithm to provide a robust means of testing this idea, through examination of an ensemble of models that satisfactorily fit the data. This can be done with no explicit regularization and without the need for subjective choices associated with binning of phase data. In addition, uncertainty bounds are calculated for anisotropic parameters using a likelihood ratio approach. We find evidence to suggest that commonly employed spatial averaging (binning) methods may be detrimental to obtaining reliable results. We conclude that there is no significant change in the strength of anisotropy with depth in the IC. Instead, we find a change in the slow direction of anisotropy to 54° within the innermost IC at an ∼650 km radius with fast direction parallel to the Earth's rotational axis.

Febrero de 2021
A long lived planetesimal dynamo powered by core crystallization
Authors: Clara Maurel, James F. J. Bryson et al
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The existence of numerous iron meteorite groups indicates that some planetesimals underwent melting that led to metal‐silicate segregation, sometimes producing metallic cores. Meteorite paleomagnetic records suggest that crystallization of these cores led to the generation of dynamo magnetic fields. Here we describe the magnetic history of the partially differentiated IIE iron meteorite

parent body. This is the first planetesimal for which we have a time resolved paleomagnetic record constrained by 40Ar/39Ar chronometry spanning several tens of million years (Ma). We find that the core of the IIE parent body generated a dynamo, likely powered by core crystallization, starting before 78 ± 13 Ma after solar system formation and lasting at least 80 Ma. Such extended core crystallization suggests that the core composed a substantial fraction of the body (urn:x-wiley:00948276:media:grl61991:grl61991-math-000113 20% core to body radius ratio depending on the body's radius), indicating efficient core formation within some partially differentiated planetesimals.

Febrero de 2021
High Frequency Seismic Events on Mars Observed by InSight
Authors: Martin van Driel, Savas Ceylan et al
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The seismometer deployed on the surface of Mars as part of the InSight mission (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) has recorded several hundreds of marsquakes in the first 478 sols after landing. The majority of these are classified as high‐frequency (HF) events in the frequency range from approximately 1 to 10 Hz on Mars' surface. All the HF events excite a resonance around 2.4 Hz and show two distinct but broad arrivals of seismic energy that are separated by up to 450 s. Based on the

frequency content and vertical to horizontal energy ratio, the HF event family has been subdivided into three event types, two of which we show to be identical and only appear separated due to the signal‐to‐noise ratio. We show here that the envelope shape of the HF events is explained by guided Pg and Sg phases in the Martian crust using simple layered models with scattering. Furthermore, the relative travel times between these two arrivals can be related to the epicentral distance, which shows distinct clustering. The rate at which HF events are observed varies by an order of magnitude over the course of one year and cannot be explained by changes of the background noise only. The HF content and the absence of additional seismic phases constrain crustal attenuation and layering, and the coda shape constrains the diffusivity in the uppermost shallow layers of Mars.

Febrero de 2021
Bayesian integration using resistivity and lithology for improving estimation of hydraulic conductivity
Authors: Shih-Yang Cheng and Kuo-Chin Hsu
Link: Click here

The characterization of spatially heterogeneous hydraulic conductivity (K) is important in groundwater resources management. We propose a Bayesian statistical method that integrates multiple secondary data (continuous and category data) with primary data (K) to improve regional K field characterization. Considering the disparity of the data scale, spatial scarcity of primary and secondary data, and need for regional‐scale site characterization, the aquifer thickness is used as the scale for data integration. We transform the high-resolution secondary data to the scale of K and perform linear/nonlinear regression analyses for the transformed secondary data and primary data. A Bayesian approach using

Metropolis within Gibbs sampling is developed for jointly integrating the primary and transformed secondary data without a limitation on the type of data attribute and the number of data set. A synthetic example is first presented to demonstrate the capability of the proposed method. Results show that the correlation strength, not the relation type, is the primary factor for improving the estimates. The Bayesian method is applied to Choushui River alluvial fan in Taiwan. Resistivity logs and a lithological description are first upscaled and then simultaneously integrated in the K estimation. Results indicate that the improvement of the K estimate obtained using resistivity data is higher in the proximal and mid fans but lower in the distal fan compared to that obtained using lithofacies data. Jointly integrating two‐attribute data outperforms using one or no secondary data set for K estimates. The proposed Bayesian integration method is thus versatile and suitable for large-scale aquifer characterization.

Febrero de 2021
Real-time Earthquake Early Warning with Deep Learning: Application to the 2016 M 6.0 Central Apennines, Italy Earthquake
Authors: Xiong Zhang, Miao Zhang et al
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Earthquake early warning systems are required to report earthquake locations and magnitudes as quickly as possible before the damaging S wave arrival to mitigate seismic hazards. Deep learning techniques provide potential for extracting earthquake source information from full seismic waveforms instead of seismic phase picks. We developed a novel deep learning earthquake early

warning system that utilizes fully convolutional networks to simultaneously detect earthquakes and estimate their source parameters from continuous seismic waveform streams. The system determines earthquake location and magnitude as soon as very few stations receive earthquake signals and evolutionarily improves the solutions by receiving continuous data. We apply the system to the 2016 M 6.0 Central Apennines, Italy Earthquake and its first-week aftershocks. Earthquake locations and magnitudes can be reliably determined as early as four seconds after the earliest P phase, with mean error ranges of 8.5–4.7 km and 0.33–0.27, respectively.

Enero de 2021
Potential link between 2020 Mentone, West Texas M5 earthquake and nearby wastewater injection: implications for aquifer mechanical properties
Authors: Sui Tung, Guang Zhai et al
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The M5 Mentone earthquake that occurred on March 26, 2020, was the largest event recorded over the last two decades in West Texas within the Delaware Basin, a U.S. major petroleum producing area. Also, numerous hydrofracturing and wastewater disposal wells are spread across this region. Within

a 30 km distance to mainshock, eight class II injection wells for industrial wastewater disposal target the deep porous Ellenburger aquifer at an average rate of 1.36x106 BBL/mo during 2012-2020. Poroelastic models of fluid diffusion show these nearby injectors collectively imparted up to 80.5 kPa of Coulomb stress at the mainshock location, capable of triggering this M5 event. Assuming the Mentone event occurs when pore pressure increase is maximum, the time delay between peak injection and the M5 occurrence corresponds with an optimal permeability of 6.76x10-14 m2 for the Ellenburger aquifer layer, in agreement with independent estimates.

Enero de 2021
Tidal influence on seismic activity during the 2011-2013 El Hierro volcanic unrest
Authors: Luis Miguel Sanz, Pablo J. González et al
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The El Hierro volcanic unrest started in July 2011, with an increase in observed seismicity rates and surface deformation. After the initial onset, hypocenters migrated southward through September 2011, culminating in a submarine eruption beginning on October 10, 2011 and finishing in February 2012. The seismic activity continued, with remarkable periods of unrest through 2012 and 2013. The most significant episodes of seismic activity during this unrest are related to magma migration at depth. In this work, we compute tidal stress for each earthquake, at its

hypocenter depth, and assign them a tidal stress phase angle. We have found statistically significant correlations between the occurrence of earthquakes and tidal stress phase angles, corresponding mainly to increasing tidal stress change rates. We found primarily that the magnitude of vertical and E‐W horizontal tidal stress values and their changing rates with time were correlated with earthquake occurrence times. We also found that there is no correlation between tides and seismicity at times with no observed surface displacements, suggesting that tidal modulation might be related to overpressure during migration of magma. Tidal modulation changes with depth and the influence of ocean‐loading tides is stronger than the influence of solid Earth tides. Our results support the hypothesis that tidal stress may modulate the seismicity during volcanic unrest, particularly during shallow depth magma migration.

Diciembre de 2020
Probabilistic Geomagnetic Storm Forecasting via Deep Learning
Authors: Adrian Tasistro-Hart, Alexander Grayver et al
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Geomagnetic storms, which are governed by the plasma magnetohydrodynamics of the solar-interplanetary-magnetosphere system, entail a formidable challenge for physical forward modeling. Yet, the abundance of high quality observational data has been amenable for the application of data-hungry neural networks to geomagnetic storm forecasting. Almost all Geomagnetic storms, which are governed by the plasma magnetohydrodynamics of the solar-interplanetary-magnetosphere system, entail a formidable challenge for physical forward.

modeling. Yet, the abundance of high quality observational data has been amenable for the application of data-hungry neural networks to geomagnetic storm forecasting. Almost all applications of neural networks to storm forecasting have utilized solar wind observations from the Earth-Sun first Lagrangian point (L1) or closer and generated deterministic output without uncertainty estimates. Furthermore, forecasting work has focused on indices that are also sensitive to induced internal magnetic fields, complicating the forecasting problem with another layer of non-linearity. We address these points, presenting neural networks trained on observations from both the solar disk and the L1 point. Our architecture generates reliable probabilistic forecasts over Est, the external component of the disturbance storm time index, showing that neural networks can gauge confidence in their output.

Diciembre de 2020
Reconstruction of GRACE Total Water Storage Through Automated Machine Learning
Authors: Alexander Y. Sun, Bridget R. Scanlon et al
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The Gravity Recovery and Climate Experiment (GRACE) satellite mission and its follow-on, GRACE-FO, have provided unprecedented opportunities to quantify the impact of climate extremes and human activities on total water storage at large scales. The approximately one-year data gap between the two GRACE missions needs to be filled to maintain data continuity and maximize mission benefits. In this study, we applied an automated machine learning (AutoML) workflow to perform gridwise GRACE-like data reconstruction. AutoML represents a new paradigm for optimal algorithm selection, model structure selection, and hyperparameter tuning, addressing some of the most challenging issues

in machine learning applications. We demonstrated the workflow over the conterminous U.S. (CONUS) using six types of machine learning models and multiple groups of meteorological and climatic variables as predictors. Results indicate that the AutoML-assisted gap filling achieved satisfactory performance over the CONUS. On the testing data, the mean gridwise Nash-Sutcliffe efficiency is around 0.85, the mean correlation coefficient is around 0.95, and the mean normalized root-mean square error is about 0.09. Trained models maintain good performance when extrapolating to the mission gap and to GRACE-FO periods (after 2017/06). Results further suggest that no single algorithm provides the best predictive performance over the entire CONUS, stressing the importance of using an end-to-end workflow to train, optimize, and combine multiple machine learning models to deliver robust performance, especially when building large-scale hydrological prediction systems and when predictor importance exhibiting strong spatial variability.

Diciembre de 2020
Complex Basement-Involved Contractional Structures in the Pre-Andean Basins of Northern Chile: A Review from Seismic Data
Authors:F. Martínez, B. Muñoz et al
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For many years, the geometry, kinematic, and the age of the basement-involved structures of the Pre-Andean basins of northern Chile have been debated. Even, many tectonic models supported by surface geological data have ignored how is the continuity of these structures in the subsurface, and also their possible relation with ancient pre-orogenic structures, thus difficulting the understanding of the main tectonic mechanisms that acted during the Andean uplift. To solve this problem, we discussed in this study the geometry and timing of the basement-involved contractional structures present in the Pre-Andean basins of northern Chile. We present field and seismic evidences of different basement-involved structural styles, including reverse faults, inverted normal faults, basement thrust ramps, and rotated and reworked basin margins, and use it them to produce three large structural cross-sections showing the geometries and

distribution of structures along the inner forearc region. The structures are interpreted to have resulted from basin inversion, which was followed by large reverse faulting accumulating 43 km in the Salar de Atacama, 10 km in the Salar de Punta Negra and 27 km in the Salar de Pedernales. Major reverse faults are predominantly located along the western and eastern edges of the basins, whereas inverted normal faults, basement thrust ramps, and othe structures are confined to the central sections. In this context, large basement thrust ramps and reverse faults are the most effective structures for generating crustal thickening. Previous analyses (U-Pb dating) of synorogenic deposits over inverted structures and apatite fission track data from Paleozoic basement pre-rift rocks suggest that contraction in the region began in the Late Cretaceous-Paleocene and continued throughout the Cenozoic; however, basement rocks experienced rapid cooling due to tectonic uplift during the Eocene. Further, the results indicate that basement-involved contractional structures are not only generated by flat-slab subduction processes, as observed in other regions of northern Chile (e.g., Frontal Cordillera). Finally, we conclude that the observed structural complexity predominantly results from the initial distribution of pre-orogenic extensional structures.

Diciembre de 2020
Analytical Prediction of Seismicity Rate Due to Tides and Other Oscillating Stresses
Authors: Elías R. Heimisson, Jean-Philippe Avouac et al
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Oscillatory stresses are ubiquitous on Earth and other solid‐surface bodies. Tides and seasonal signals perpetually stress faults in the crust. Relating seismicity to these stresses offers fundamental insight into earthquake triggering. We present a simple model that describes seismicity rate due to perpetual oscillatory stresses. The model applies to large-amplitude,

nonharmonic, and quasiperiodic stressing. However, it is not valid for periods similar to the characteristic time ta. We show that seismicity rate from short‐period stressing scales with the stress amplitude, but for long periods with the stressing rate. Further, that background seismicity rate r is equal to the average seismicity rate during short‐period stressing. We suggest that Aσ0 may be underestimated if stresses are approximated by a single harmonic function. We revisit Manga et al. (2019, https://doi.org/10.1029/2019GL082892), which analyzed the tidal triggering of marsquakes and provide a rescaling of their seismicity rate response that offers a self‐consistent comparison of different hydraulic conditions.

Noviembre de 2020
A Machine Learning-Based Detection of Earthquake Precursors Using Ionospheric Data
Authors: A. A. Akyol, O. Arikan et al
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Detection of precursors of strong earthquakes is a challenging research area. Recently, it has been shown that strong earthquakes affect electron distribution in the regional ionosphere with indirectly observable changes in the ionospheric delays of GPS signals. Especially, the total electron content (TEC) estimated from GPS data can be used in the seismic precursor detection for strong earthquakes. Although physical mechanisms are not well understood yet, GPS‐based seismic precursors can be observed days prior to the occurrence of the earthquake. In this study, a novel machine learning‐based technique, EQ-PD, is proposed

for detection of earthquake precursors in near real time based on GPS‐TEC data along with daily geomagnetic indices. The proposed EQ‐PD technique utilizes support vector machine (SVM) classifier to decide whether an observed spatiotemporal anomaly is related to an earthquake precursor or not. The data fed to the classifier are composed of spatiotemporal variability map of a region. Performance of the EQ‐PD technique is demonstrated in a case study over a region covering Italy in between the dates of 1 January 2014 and 30 September 2016. The data are partitioned into three nonoverlapping time periods, that are used for training, validation, and test of detecting precursors of earthquakes with magnitudes above 4 in Richter scale. The EQ‐PD technique is able to detect precursors in 17 out of 21 earthquakes while generating 7 false alarms during the validation period of 266 days and 22 out of 24 earthquakes while generating 13 false alarms during the test period of 282 days.

Noviembre de 2020
Machine Learning-Based Analysis of Geological Susceptibility to Induced Seismicity in the Montney Formation, Canada
Authors: Paulina Wozniakowska and David W. Eaton
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We analyze data from 6,466 multistage horizontal hydraulic fracturing wells drilled into the Montney Formation over a large region in western Canada to evaluate the impact of geological, geomechanical, and tectonic characteristics on

the distribution of hydraulic fracturing-induced seismicity. Logistic regression was used to obtain a machine learning estimate of the seismogenic activation potential of each well. Our results fit the observed spatial variability, including an enigmatic change in seismicity at 120°W that does not correlate with any change in industrial activity. Feature importance analysis provides insight into data types that have the greatest impact on the results. Based on current data, seismogenic activation potential is most strongly influenced by depth of injection and distance of the well to the Cordilleran thrust belt.

Noviembre de 2020
Modern Meteoric 36Cl Deposition in the Atacama Desert, Chile
Authors: Fan Wang and Greg Michalski
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36Cl is a radioactive chlorine isotope found in the atmosphere and can be used in many ways, from determining ages of soils and groundwaters to tracing origins of salts and groundwater flow paths. In order to use meteoric 36Cl, we must know how much is deposited from the

atmosphere to the surface. There are only a few studies of 36Cl deposition in southern hemisphere, even less in extraordinarily dry environments, which hinders its use in desert regions south of the equator. We have measured the 36Cl deposition along a west‐east transect in the Atacama Desert in northern Chile and developed a simple explanation for our results. Future work will use this deposition rate to determine the duration of soil salt accumulation in the Atacama and understand changes in climate (precipitation) in the past.

 

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