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The net Arctic sea-ice area (SIA) can be estimated from the routine monitoring of sea-ice concentration (SIC) by passive microwave measurements from satellites. To be a truly useful metric, for example, of the sensitivity of the Arctic sea-ice cover to global warming, we need, however, reliable estimates of its uncertainty. We here derive this uncertainty by taking spatial and temporal error correlations of the underlying local sea ice concentration products into account. Doing so, we find that the observational uncertainties of both sea-ice area and sea-ice extent (SIE) in 2015 are about 300 000 km2 for daily and weekly estimates and 160 000 km2 for monthly estimates. This is about half of the spread in estimated sea-ice area from different passive microwave SIC products, showing that random SIC errors play at least as much a role in SIA uncertainties as inter-SIC-product biases. We further show that the trend of SIA in September, which is traditionally the month with least Arctic sea ice is 105 000 km2 a-1 ± 9 000 km2 a-1 for the period from 2002 to 2017. This is the first estimate of a SIA trend with an explicit representation of temporal error correlations. [ABSTRACT FROM AUTHOR]

The current state‐of‐the‐art of satellite gravity data processing makes use of de‐aliasing products to reduce high‐frequency mass anomalies. For example, the most recent official Atmosphere and Ocean De‐aliasing products (AOD1B‐RL06) are applied for the Gravity Recovery and Climate Experiment (GRACE) and GRACE‐Follow On (GRACE‐FO) missions. The temporal resolution of AOD1B‐RL06 is 3 h, and spectrally, they are computed up to degree and order 180. In this study, we explore a refined, e.g., geometrically, physically, and numerically improved, mass integration approach that is important for computing the atmosphere part of these products. Besides, the newly available ERA5 climate data are used to produce a new set of non‐tidal atmosphere de‐aliasing product (HUST‐ERA5) that is computed hourly up to degree and order 100, covering 2002 onwards. Despite an overall agreement with AOD1B‐RL06 (correlation≥0.99), considerable discrepancies still exist between HUST‐ERA5 and AOD1B‐RL06. The possible reasons are therefore analyzed, and we find the input climate data, sampling rate and integration method may result in a product difference of ∼0.3, ∼0.15 and ∼0.05 millimeter geoid height, respectively. The total differences between HUST‐ERA5 and AOD1B‐RL06 can lead to a mean variation of ∼7.34 nm/s on the laser ranging interferometry (LRI) range‐rate residuals, for example, during January 2019, which is already close to the LRI precision. This impact is invisible for the GRACE (‐FO) gravity inversion because of the less accurate on‐board KBR (K‐band ranging) instrument, however, it will be non‐negligible and should be considered when the LRI completely replaces the KBR in the future gravity missions. Plain Language Summary: Time‐variable GRACE and GRACE‐FO satellite gravity data are unique remote sensing products that can be used for studying mass changes related to for example, water variability in aquifers, continental ice‐sheets, and oceans. The current state‐of‐the‐art of GRACE (‐FO) data processing makes use of background de‐aliasing products to reduce high‐frequency mass anomalies to focus on the dominant hydrology related signals. Thus, any errors in these products will badly affect the quality of water mass estimations. In this study, we explore a refined, that is, geometrically, physically, and numerically improved, mass integration approach to use the newly available ERA5 weather data for computing the atmosphere part of the background non‐tidal de‐aliasing products. The new set is called HUST‐ERA5 that is computed hourly up to degree and order 100, covering 2002 onwards, and freely available for download. Here we show that replacing the official de‐aliasing products with HUST‐ERA5 can lead to a mean variation of 7.34 nm/s on the Laser Ranging Interferometry (LRI) residuals, which is close to the LRI precision. This impact is invisible for the GRACE (‐FO) data because of the less accurate on‐board ranging instrument. However, it will be non‐negligible and should be considered when the LRI is functional in the future gravity missions. Key Points: Hourly ERA5 reanalysis is employed to generate the atmosphere de‐aliasing product for the first time, through a refined 3‐D vertical integration methodThe use of input fields from ERA5 and increasing the sampling rate of atmospheric products to 1 h are recommended for Gravity Recovery and Climate Experiment‐Follow On and future missionsNew sets of hourly atmospheric non‐tidal de‐aliasing and tidal components including [S1,S2,P1,K1,N2,M2,L2,T2,R2,T3,R3,S3] are produced and freely shared [ABSTRACT FROM AUTHOR]

We investigate the veracity of the reports by Iwata and Umeno (2016, https://doi.org/10.1002/2016ja023036) and Iwata and Umeno (2017, https://doi.org/10.1002/2017ja023921), both of which claimed that the observed perturbations in Global Navigation Satellite System (GNSS)‐based ionospheric total electron content (TEC) could serve as a "precursor" of large earthquakes based on correlation analysis. Iwata and Umeno (2016, https://doi.org/10.1002/2016ja023036) defined a spatial correlation of residuals between the observed and predicted TEC time series. They reported that the correlation value is significantly larger before large earthquakes than those observed during non‐earthquake periods. Iwata and Umeno (2017, https://doi.org/10.1002/2017ja023921), who applied the same method to other large earthquake, claimed that the preseismic ionospheric disturbances can be distinguished from other non‐earthquake phenomena based on the small percentage of area where the correlation value exceeds the criterion. They also claimed that the low propagation velocity of the correlation peaks is also a preseismic characteristic. Here we tested their claims using a larger data set. As a result, these three characteristics they claimed to have captured as evidence of earthquake precursors are not significant being frequently observed during normal (nonearthquake) days. In addition to that, the criteria of Iwata and Umeno (2017, https://doi.org/10.1002/2017ja023921) cannot be applied to the large earthquake discussed by Iwata and Umeno (2016, https://doi.org/10.1002/2016ja023036), and vice versa. Therefore, we can find no basis for claiming that they detected precursors to the earthquakes. The calculation procedure of the correlation function shows that the value is more of an indicator that amplifies small variations synchronized between nearby stations, like medium‐scale traveling ionospheric disturbances rather than earthquake precursors. Key Points: Preseismic anomalies detected by correlation analysis by Iwata and Umeno (2016) is not significant compared with that on nonearthquake daysAnomalous area rate proposed as precursor in Iwata and Umeno (2017) is not significant and not applicable to their previous Iwata and Umeno (2016)Propagation velocity of total electron content (TEC) anomaly proposed by Iwata and Umeno (2017) is not significant as well [ABSTRACT FROM AUTHOR]

A geomagnetic storm is a phenomenon of weakening of Earth's magnetic field from a few hours to several days, which directly or indirectly affects navigation, transportation, communication, power grids, satellite electronics, etc. In general, the duration of the recovery phase is larger. Thus, its cumulative effect is greater than the main phase. Therefore, it is important to understand the physical processes involved during the recovery phase. In this paper, we have studied the recovery phase of 31 extreme geomagnetic storms that occurred from 1990 to 2020. Each storm demonstrates two distinct features of the recovery phase that is, initial fast and later slow recovery phase. During the fast recovery phase, the rate of recovery either linearly or non‐linearly depends on SYM−H, which has been characterized by an exponential or hyperbolic decay function in various reported studies. In our study, we have noted that the hyperbolic function explains the complete recovery phase of only 11 extreme events. Furthermore, both decay functions fail to explain the late recovery phase of storms. Interestingly, we have found that the rate of recovery during the slow phase shows steady variation (independent to SYM−H), that is, d(SYM−H)dt=constant. Our analysis suggests that the magnitude of the recovery rate during the late phase is proportional to the magnitude of the storm. Key Points: The exponential or hyperbolic decay function can only explain fast recovery phase of a stormsWe observe a constant recovery rate during the late (slow) recovery phase of extreme storms that is, d(SYM−H)dt=constantWe also find that the recovery rate during the late phase is directly proportional to the amplitude of the storm [ABSTRACT FROM AUTHOR]

The coupling between a rapidly expanding cloud of ionized debris and an ambient magnetized plasma is revisited with a hybrid (kinetic ion/fluid electron) simulation code that allows a study over a wide range of plasma parameters. Over a specified range of hypothetical conditions, simple scaling laws in terms of the total debris mass and explosion speed are derived and verified for the maximal size of the debris cloud and the fraction of debris that free‐streams from the burst along the magnetic field. The amount of debris that escapes from the burst with minimal coupling to the background magnetic field increases with the debris gyroradius. Test cases with two different debris species—including a heavy minority species with a relatively large gyroradius—highlight how the collisionless coupling of the debris depends on the single particle trajectories as well as the overall conservation of energy and momentum. Plain Language Summary: An astrophysical explosion is the rapid expansion of a cloud of ionized debris into a surrounding magnetized plasma. Examples include supernova remnants, targets hit by lasers in laboratory experiments, and active experiments in space where barium or other material is rapidly released. We systematically study the dependence of the distance the debris travels on its initial speed and on the total quantity of exploded mass. We also formulate simple estimates for the fraction of the debris that escapes along the magnetic field without losing much energy. Key Points: With hybrid particle‐in‐cell simulations, we formulate scalings for the size of an astrophysical explosion over a range of parametersTransport across the magnetic field by flute modes is quantifiedEstimates are developed for the fraction of the total debris that exits the explosion in free‐streaming beams along the magnetic field [ABSTRACT FROM AUTHOR]

Peer reviewing is the selfless act of evaluating and providing feedback on scientific papers submitted in journals like JGR: Planets. Every review is written with the objective of clarifying the article and often contains suggestions for additional analyses or topics of discussion. Reviewers often spend hours examining the rigor of the methods, the validity of the results, and the significance of the conclusions in the submitted manuscripts. The extra effort of our pool of reviewers in a year when we all needed to adjust our daily routines in response to a pandemic has not gone unnoticed. In 2020, JGR: Planets benefited from 1,168 reviews provided by 705 unique reviewers. We are particularly grateful to the scientists who remained involved in the review process. We also understand that many of us had to reduce our reviewing commitment this year. Hopefully, the coming year will see a return to normalcy in your lives. To our reviewers, past, present, and future, the entire editorial board of JGR: Planets wishes to express here our most heartfelt gratitude. Thank you! Plain Language Summary: Peer review relies on the dedication of volunteer scientists who spend hours evaluating the submitted manuscripts and suggesting ways to improve them. In 2020, JGR: Planets benefited from 1,168 reviews provided by 705 unique reviewers. We are particularly grateful to the scientists who remained involved in the review process in an especially challenging year. We also keep in our thoughts those who had to reduce their reviewing commitment this year as the pandemic and other events upset their daily lives. To our reviewers, past, present, and future, the entire editorial board of JGR: Planets wishes to express here our most heartfelt gratitude. Thank you! Key Points: Peer review is a crucial component of the high‐quality planetary science published in JGR: PlanetsIn 2020, 705 individuals provided 1,168 reviews of papers submittedPeer reviewers: thank you for your service to the planetary community [ABSTRACT FROM AUTHOR]

Here we are presenting a statement of Diversity, Equity and Inclusion (DEI) for JGR: Biogeosciences. This statement includes current policies and practices, and details concrete actions that we intend to implement over the next year to better include underrepresented groups in the publication process. Key Points: The impact of our journal is enhanced when a representative pool of contributors participates in the process of scientific publicationIncreasing reviewer and editor diversity is the best opportunity we have to remove bias from the peer review processKey priorities to expand and diversify our editorial, reviewing, and publishing community are highlighted [ABSTRACT FROM AUTHOR]

With the objective to identify the structures that represent the metalogenic structural control of auriferous zone, and to propose new zones with possible auriferous mineralization, in La Union - La Botija, provinces Camagüey - Las Tunas, Cuba it was carry out an integraed interpretation of come geophysical methods and the relief. The processing of the gravimetric and magnetic data was made to determine horizontal gradients in the different directions that suggest fault presence. The processing of the radiometric allows the evaluation of the mineralization factor and the creation of ternary maps. From the digital elevation model data it was obtained the drainage system and the maps of flow accumulation. It was accomplished the interpretation of every one of the generated maps and the integrated interpretation of them; that allowed identifying a large number of structures, and zones with hydrothermal. It was identified six possible zones of auriferous mineralization, according to geology geophysical and relief criteria. These results show the presence of new appropriate sectors for the recognition of auriferous mineralization which proves to be at the present time because they are in the frame of the National Program of gold that the Geological National Service execute. [ABSTRACT FROM AUTHOR]

Influences of the ocean mixed layer (OML) dynamics on intensity, pathway, and landfall of October 2012 Hurricane Sandy were examined through an experiment using the Weather Research and Forecasting (WRF) model. The WRF model was run for two cases with or without coupling to the OML. The OML in the WRF was calculated by an oceanic mixed layer submodel. The initial conditions of the depth and mean water temperature of the OML were specified using Global-FVCOM and Global-HYCOM fields. The comparison results between these two cases clearly show that including the OML dynamics enhanced the contribution of vertical mixing to the air-sea heat flux. When the hurricane moved toward the coast, the local OML rapidly deepened with an increase of storm wind. Intense vertical mixing brought cold water in the deep ocean toward the surface to produce a cold wake underneath the storm, with the lowest sea temperature at the maximum wind zone. This process led to a significant latent heat loss from the ocean within the storm and hence rapid drops of the air temperature and vapor mixing ratio above the sea surface. As a result, the storm was intensified as the central sea level pressure dropped. Improving air pressure simulation with OML tended to reduce the storm size and strengthened the storm intensity and hence provided a better simulation of hurricane pathway and landfall. [ABSTRACT FROM AUTHOR]

In this study, the potential for sea ice concentration prediction using machine-learning methods is investigated. Three different sea ice prediction models are compared: one high-resolution dynamical assimilative model and two statistical machine-learning models. The properties of all three models are explored, and the quality of their forecasts is compared. The dynamical model is a state-of-the-art coupled ocean and sea ice ensemble-prediction system with assimilation. The observations assimilated are high-resolution sea ice concentration from synthetic aperture radar (SAR) and sea surface temperature from infrared instruments. The machine-learning prediction models are a fully convolutional network and a k-nearest neighbors method. These methods use several variables as input for the prediction: sea ice concentration, sea surface temperature, and 2-m air temperature. Earlier studies have applied machine-learning approaches primarily for seasonal ice forecast. Here we focus on short-term predictions with a length of 1-4 weeks, which are of high interest for marine operations. The goal is to predict the future state of the sea ice using the same categories as traditional ice charts. The machine-learning forecasts were compared to persistence, which is the assumption that the sea ice does not change over the forecasting period. The machine-learning forecasts were found to improve upon persistence in periods of substantial change. In addition, compared to the dynamical model, the k-nearest neighbor algorithm was found to improve upon the 7-day forecast during a period of small sea ice variations. The fully convolutional network provided similar quality as the dynamical forecast. The study shows that there is a potential for sea ice predictions using machine-learning methods. [ABSTRACT FROM AUTHOR]

The anomaly maps and amplitude and wavelength changes of the anomalies obtained from gravity and magnetic methods can provide to identify fault traces in the underground. The Tuzgölü Fault Zone (TFZ), the NW-SE striking active fault zone in central Anatolia, includes fault strands that cut the basement and basin deposits. Our magnetic and gravity analysis suggests that Tuzgölü Basin and its surroundings are characterized by distinct depression and ridge areas. Gravity anomaly data show the presence of faults at depths of sea level (0 m), -1000 m, -2000 m, -3000 m, and -4000 m. These faults are mostly normal and reverse faults, as well as the lesser amount of vertical faults (high-angle normal/reverse faults) with NW-SE, N-S, and NE-SW-striking. The normal faults are of the structural development and the deposition of the Tuzgölü Basin units, which occurred late Cretaceous-Middle Eocene and Early Miocene-Quaternary Periods. The reverse faults originated from the result of the regional-scale compressional regime during Middle Eocene-Late Oligocene/Early Miocene based on the fault dating data from the literature. The active TFZ, including several fault strands, are relatively younger faults in the region that have initiated to develop during faulting events from after Middle Miocene or Early Pliocene. [ABSTRACT FROM AUTHOR]

Peatlands play a key role in the global carbon cycle, sequestering and releasing large amounts of carbon. Despite their importance, a reliable method for the quantification of peatland thickness and volume is still missing, particularly for peat deposits located in the tropics given their limited accessibility, and for scales of measurement representative of peatland environments (i.e., of hundreds of km2). This limitation also prevents the accurate quantification of the stored carbon as well as future greenhouse gas emissions due to ongoing peat degradation. Here we present the results obtained using the airborne electromagnetic (AEM) method, a geophysical surveying tool, for peat thickness detection at the landscape scale. Based on a large amount of data collected on an Indonesian peatland, our results show that the AEM method provides a reliable and accurate 3‐D model of peatlands, allowing the quantification of their volume and carbon storage. A comparison with the often used empirical topographic approach, which is based on an assumed correlation between peat thickness and surface topography, revealed larger errors across the landscape associated with the empirical approach than the AEM method when predicting the peat thickness. As a result, the AEM method provides higher estimates (22%) of organic carbon pools than the empirical method. We show how in our case study the empirical method tends to underestimate the peat thickness due to its inability to accurately detect the large variability in the elevation of the peat/mineral substrate interface, which is better quantified by the AEM method. Plain Language Summary: Peatlands store in their soils about the same amount of carbon present in the vegetation biomass. Peat degradation due to human interventions (as for example soil drainage) and fires that occur during severe droughts release several gigatons of carbon dioxide and other greenhouse gases (GHGs) every year. The accurate assessment of the carbon stored in peatlands is of key importance to implement effective strategies to mitigate climate change, promoting conservation actions, and avoiding potential GHG emissions. In this research, we compare two methods that allow us to construct a 3‐D model of peatlands. Applying the methods to a large study site in Indonesia, we show how a geophysical method called airborne electromagnetics allows for a more accurate quantification of the peat volume and the organic carbon pool. Key Points: The airborne electromagnetic (AEM) method can detect both the top and the bottom of a peatland over large areas at high spatial resolutionA correlation between the peat thickness and surface topography is common in some dome‐shaped peatlands around the worldThe peatland 3‐D model retrieved with AEM is superior if compared to the empirical approach that links peat thickness to only soil elevation [ABSTRACT FROM AUTHOR]

This special collection, sponsored by National Aeronautics and Space Administration's Solar System Exploration Research Virtual Institute, includes contributions relevant to the science and exploration of Moon, near‐Earth asteroids, and the moons of Mars. Contributions appear in the Journal of Geophysical Research—Planets, Earth and Space Science, and GeoHealth. Major topics covered by the contributions include, but are not limited to, space weathering, geologic analysis of potential lunar landing sites, field analog investigations, and infrared spectroscopic measurements applied to airless bodies in the solar system. Plain Language Summary: National Aeronautics and Space Administration's Solar System Exploration Research Virtual Institute (SSERVI) promotes the science and exploration of the Moon, near‐Earth Asteroids, and the moons of Mars. This special collection includes contributions relevant to this mission by SSERVI team members and the broader science community. Key Points: SSERVI works to advance basic and applied research fundamental to lunar and planetary science and to advance human exploration of the solar system through scientific discoveryThis special collection includes contributions from both SSERVI team members and nonteam members related to science and exploration of the Moon, near‐Earth asteroids, and the moons of MarsContributions highlight how remote sensing, laboratory geologic analyses, field work, and medical studies contribute to SSERVI's science and exploration plans [ABSTRACT FROM AUTHOR]

While it has been shown that the mechanical properties and the reactivity of carbonate‐bearing rocks may be influenced by the chemical composition of the fluids, little is known about how the fluid composition affects their frictional response. Here, we have used atomic force microscopy to investigate the frictional characteristics of single calcite crystals in calcium carbonate saturated solutions and in two brines, NaCl and CaCl2, at a wide range of geologically relevant concentrations. Surface forces were measured to determine the ion‐specific composition of the confined fluid films and the adhesion between the confining surfaces. The effect of fluid chemistry on calcite's (dynamic) frictional response significantly depends on the normal stress. At low stresses, the confined fluid film lubricates the single‐asperity contact efficiently, resulting in low friction coefficients, especially in the case of NaCl solutions. When the pressure solution of calcite is triggered at sufficiently high stress, a significant reduction of the friction coefficient was observed, and in this case, CaCl2 solutions were shown to promote this frictional weakening more significantly than NaCl. This is the first experimental investigation of the ion‐specific frictional characteristics of calcite at the level of a single‐asperity contact. The presence of infiltrated fluids in carbonate faults may also play a critical role in fault dynamics. Hence, the results of this nanoscale study are extrapolated to carbonate fault friction in the presence of infiltrated fluids, and they contribute to advance our understanding of induced seismicity at geological scale. Key Points: The frictional behavior of calcite was measured in CaCl2 and NaCl solutions by atomic force microscopy, and it was observed to depend on the normal stress, the sliding velocity, and the fluid compositionAt low normal stress, the confined fluid film lubricates the single‐asperity contact efficiently, resulting in low friction, and the friction is lower in NaCl solutionsWhen pressure solution is triggered at sufficiently high normal stresses, a significant weakening of the friction force is observed; this results in a decrease in friction, which is more prominent in CaCl2 brines [ABSTRACT FROM AUTHOR]

Triaxial experiments and direct fluid injection experiments have been conducted at confining pressures up to 100 MPa on Mancos shale, Whitby mudstone, Penrhyn slate, and Pennant sandstone. Experiments were conducted with sample axes lying both parallel and perpendicular to layering in the materials. During triaxial failure Penrhyn slate was stronger for samples with cleavage parallel to maximum principal stress, but the two orientations in the shales displayed similar failure stresses. Initial flaw sizes of around 40 μm were calculated from the triaxial data using the wing crack model, with the shales having shorter initial flaws than the nonshales. During direct fluid injection, breakdown was rapid, with no discernible gap between fracture initiation and breakdown. Breakdown pressure increased linearly with confining pressure but was less sensitive to confining pressure than expected from existing models. A fracture mechanics‐based model is proposed to determine the initial flaw size responsible for breakdown in injection experiments. Flaw sizes determined in this way agree reasonably with those determined from the triaxial data in the nonshales at low confining pressures. As confining pressure rises, a threshold is reached, above which the fluid injection experiments suggest a lower initial flaw length of around 10 μm. This threshold is interpreted as being due to the partial closure of flaws. In the shales an initial flaw length of around 10 μm was determined at all confining pressures, agreeing reasonably with those determined through the triaxial experiments. Key Points: Smaller flaws control sample failure in shales than in most other rock materialsBreakdown pressure increases linearly with confining pressure in fluid injection experimentsFlaws in the region of 10‐ to 40‐μm length control sample failure [ABSTRACT FROM AUTHOR]

The influence of aseismic ridges on subduction kinematics and dynamics, and on the deformation of the overriding plate, remains a topic of debate. This study presents laboratory‐based geodynamic models that simulate the process of aseismic ridge subduction below an overriding plate. The analog experiments show that, depending on its size, subduction of an aseismic ridge can impact on the kinematics of subduction, overriding plate deformation and, to a lower extent, on the geometry of the slab and that of the trench. Specifically, it can cause a reduction of the subducting plate and trench retreat velocities, decreases overriding plate extension and even drives local forearc shortening for the widest ridge, increases the slab dip angle next to the aseismic ridge, but decreases the dip angle at the aseismic ridge in case the ridge is thick and wide, and produces a local perturbation (indentation) of the trench geometry. The magnitude of the described modifications relies to a comparable extent on aseismic ridge width and thickness. The effects of aseismic ridge subduction observed in our models compare to those of the Louisville Seamount Chain, the Cocos Ridge, and the d'Entrecasteaux Ridge system in nature and provide an explanation for the local deformation observed at these subduction zones. Plain Language Summary: Subduction zones are locations where one tectonic plate sinks (subducts) beneath another plate. Beyond that simple definition, substantial differences have been documented for the current subduction systems around the globe. However, the factors controlling the different observed variables are still uncertain. One of these factors is the presence of submarine ridges on subducting oceanic plates, as these are relatively light features that reduce the bulk density of the sinking plates. What is the role of those ridges on the subduction process? We addressed this question by constructing laboratory models of subduction zones with aseismic ridges. Our experiments show that relatively large ridges allow subducting oceanic plates to sink more slowly into the Earth's mantle and remain relatively shallow. Nevertheless, these ridges cannot account for the extremely low angle at which some regions of the Nazca plate subduct below South America (the controversial "flat regions"). The margin of the overlying continental or oceanic plate is modified, developing a curvature in front of the ridges. Finally, the subduction of large ridges leads to local horizontal compression at the margin of the overlying plate, with the consequent rising of a small and isolated mountain belt like Fila Costena and Burica Peninsula in Costa Rica. Key Points: Subducting aseismic ridges have an impact on subduction geometry, kinematics and dynamics, and overriding plate deformationThe models in this study represent 200‐ to 400‐km‐wide and 12‐ to 20‐km‐thick aseismic ridges at 1,000‐km‐wide subduction zonesThe results of our analog models are compatible with data from natural subduction systems [ABSTRACT FROM AUTHOR]

Linear ultrasonic testing (LUT) has been extensively used as a tool for the evaluation of damage processes in various materials ranging from synthetic metals to natural geomaterials, such as rocks. A key limitation of LUT‐based damage studies to date is the lack of explicit evidence used in associating material damage with the changes in measured LUT attributes (e.g., ultrasonic wave amplitude and velocity). In this study, the evolution of the full‐field strains in brittle rock specimens (Lyons sandstone) subjected to failure are analyzed in real time and linked with the changes in the ultrasonic wave amplitude in localized areas illuminated by ultrasonic beams, termed as the ultrasonic image areas. The noncontact optical full‐field displacement measurement method of 2‐D digital image correlation is implemented in combination with the LUT procedure to continuously track changes in the ultrasonic wave amplitude with the evolution of strains across the surface of the uniaxially loaded intact rock specimens. The ultrasonic amplitude showed near‐linear correlation with the intensity of inelastic tensile strain recorded in the rock specimens. The results from the study corroborate that the ultrasonic changes are in fact influenced by the regions of tensile cracking, which is the primary inelastic deformation mechanism in brittle rocks. Key Points: Compressional ultrasonic wave attenuation was explicitly correlated with the stress‐induced extensile microcracks in brittle rock specimensThe intensity of extension was analyzed in the UIA by the total and nonelastic apparent tensile strain based on the critical strain limitUltrasonic amplitude showed consistent near‐linear correlation with nonelastic apparent strains above the crack initiation threshold [ABSTRACT FROM AUTHOR]

Both, the network configuration and the way of terrestrial reference frame (TRF) realization, affect the global geodetic products delivered from the Global Navigation Satellite Systems (GNSS) data processing. The purpose of this study is to analyze the differences in GNSS products, such as station coordinates, Earth rotation parameters, geocenter coordinates (GCC), and satellite orbits delivered from the double‐difference multi‐GNSS (GPS, GLONASS, and Galileo) processing, which may arise from (1) using a homogeneous and inhomogeneous network of multi‐GNSS stations, (2) different approaches to the TRF realization using minimum constraint conditions, and (3) different approaches to handling of GCC in GNSS global processing. The questionable quality of GCC delivered from the global GNSS solutions is described with a special attention to network effects and system‐specific parameters. We found that Galileo can provide GCC, whose quality corresponds to the GPS series. Moreover, the GCC from Galileo is of a better quality than those based on GLONASS data, despite the same number of nominal orbital planes and a much lower number of active satellites. When the No‐Net‐Translation constraint is not applied on the GNSS network, the station coordinate repeatability is worsened by about 70%, 55%, and 25% for the north, east, and up components, respectively, compared to the solution when applying No‐Net‐Translation and when having the network origin consistent with the international TRF. We thus infer that the No‐Net‐Translation condition is mandatory in global GNSS solutions. Key Points: Using the No‐Net‐Translation constraint in global multi‐GNSS processing is beneficial for station coordinate estimatesGalileo constellation can provide geocenter coordinates whose quality corresponds to that from GPSInhomogeneous distribution of GNSS stations leads to systematic effects in geocenter coordinates delivered from GNSS [ABSTRACT FROM AUTHOR]

We present a new, fully probabilistic and nonlinear inversion method to estimate the spatial distribution of geological properties (depositional facies, diagenetic rock types, or other rock properties) from geophysical data (e.g., seismic data). Contrary to the conventional generative approach that models solution probabilities via the likelihood of observed data, our method uses a discriminative approach that directly models the posterior distribution of the geological properties given the data. This reduces the modeling effort significantly and allows machine learning algorithms such as neural networks to be deployed to solve large geophysical inference problems. We show that our method honors spatial distributions of geological parameters supplied as prior information about local geology and can be trained using supervised learning to be robust against noise present in the data as long as we can provide statistical characteristics of the noise. Exact Bayesian inference is almost always infeasible in practice because it requires normalization of the posterior distribution; this is intractable for large models and must therefore be approximated. Most existing probabilistic inversion methods use stochastic sampling (e.g., Markov chain Monte Carlo, McMC) for approximate inference. However, McMC involves the use of subjective criteria to detect convergence. We use the variational Bayes method to transform probabilistic inference into numerical optimization. This is a more efficient, deterministic alternative to McMC‐based inference for suitably structured problems. Our method thus avoids extensive sampling during inference, yet provides fully probabilistic Bayesian results, and is therefore scalable to higher dimensional problems. Plain Language Summary: We present a new method for the estimation of geological properties such as type and physical properties of rocks, from geophysical measurements such as seismic data. Most existing methods assume that the geophysical data have been perfectly localized to produce data at each point in space (e.g., through tomography or imaging) and that the data are free of correlated noise or errors. Although neither requirement is met in reality, existing methods use these assumptions to make solutions computationally tractable. Our method removes both of these assumptions and is still computationally tractable for suitably structured problems (a class of problems that can be decomposed into interlinked subproblems). We achieve this by abandoning the usual approach of modeling the likelihood—a measure of how probable it is that the observed data were generated by any given geological model. Instead, our method models the geological parameters from the observed data directly, using examples of the direct data‐model relationship. This reduces the required computational resources significantly for large‐scale problems. To further improve computational efficiency, our method avoids extensive use of Monte Carlo sampling, and instead uses numerical optimization to estimate the desired geological properties and their fully probabilistic uncertainties. Key Points: Our fully nonlinear Bayesian inversion method requires no assumptions of localization or conditional independence of dataThe discriminative approach ensures that the method can be applied using supervised machine learningThe method performs fully nonlinear probabilistic inference while avoiding Markov chain Monte Carlo sampling [ABSTRACT FROM AUTHOR]

Along the Nankai Trough of southwest Japan, large‐magnitude interplate earthquakes (M > 8) have occurred repeatedly, with recurrence intervals of approximately 100 years. It is essential to estimate more precisely the spatial distribution of interplate coupling; that is, along‐strike and along‐dip heterogeneity of the coupling ratio defined as the slip deficit rate divided by the plate convergence rate, for understanding the mechanisms and/or assessing the potential of future mega interplate earthquakes in this region. Recently, the seafloor Global Navigation Satellite System‐Acoustic (GNSS/A) combination technique observation network has been extended, and we can now obtain crustal displacement fields for both onshore and offshore regions. In this study, we estimate interplate coupling distribution along the Nankai Trough using both seafloor GNSS/A and onshore GNSS data with the block motion model, minimizing the spatial variations of modeling uncertainties of coupling estimates. Seafloor GNSS/A data depict very strong coupling near the trough axis off of Tokai, as well as trough‐parallel heterogeneity in interplate coupling at the shallow plate interface. Using the block motion model confirmed that observed crustal deformation above the deep plate interface in SW Japan is dominated by rigid block motion rather than elastic response to slip deficit on the deep plate interface of the subducting Philippine Sea plate. The minimization of spatial variations for the modeling uncertainties of coupling estimates helps us to estimate the coupling distribution with nearly homogeneous uncertainties between offshore and onshore regions, which is useful for evaluation of interplate earthquakes and/or tsunamis hazards. Key Points: Interplate coupling along the Nankai Trough was estimated using the block motion model based on seafloor and onshore geodetic observationsSpatial variations of modeling uncertainties of coupling estimates were minimized with a new minimization algorithmVery strong coupling near the trough axis off of Tokai suggests tsunamigenesis potential at the shallowest part of plate interface [ABSTRACT FROM AUTHOR]

Understanding streaming potential generation in porous media is of high interest for hydrological and reservoir studies as it allows to relate water fluxes to measurable electrical potential distributions. This streaming potential generation results from an electrokinetic coupling due to the presence of an electrical double layer developing at the interface between minerals and pore water. Therefore, the pore sizes of the porous medium are expected to play an important role in the streaming potential generation. In this work we use 2‐D pore network simulations to study the effect of the pore size distribution upon this electrokinetic mechanism. Our simulations allow a detailed study of the influence of a large range of permeabilities (from 10−16 to 10−10 m2) for different ionic concentrations (from 10−4 to 1 mol/L). We then use and compare two different approaches that have been used over the last decades to model and interpret the streaming potential generation: the classical coupling coefficient or the effective excess charge density, which has been defined recently. Our results show that the four pore size distributions tested in the present work have a restricted influence on the coupling coefficient for ionic concentration smaller than 10−3 mol/L while it completely drives the behavior of the effective excess charge density over orders of magnitude. Then, we use these simulation results to test an analytical model based on a fractal pore size distributions. This model predicts well the effective excess charge density for all pore size distributions under the thin double layer assumption. Key Points: We simulate streaming potentials for 2‐D networks with different pore size distributionsThe pore size distribution has a very restricted influence on electrokinetic coupling coefficientsA recent effective excess charge density model accounts for all the pore size distributions [ABSTRACT FROM AUTHOR]

A wide range of mass gain in the inland of the Tibetan Plateau (TP) has been observed by the Gravity Recovery and Climate Experiment (GRACE). But there are still controversies on how to understand this phenomenon. In this paper, satellite geodesy data and hydrological models are combined and applied for extracting signals caused by tectonic processes in the TP during the period from 2003 to 2009. We find that in the inland of the TP there are three regions with a significant signal that should be attributed to tectonic processes. The three prominent mass signals, each located in the western, central, and eastern TP, are estimated to be at the rate of 1.47 ± 0.43, −0.85 ± 0.53, and 1.51 ± 0.56 cm/year, respectively, in equivalent water height. However, the rate caused by Earth surface deformation constrained by GPS is 0.33 ± 0.15/0.30 ± 0.10/0.14 ± 0.24 cm/year in equivalent water height, which cannot explain the whole tectonic signals and indicates that a significant mass change occurs beneath the crust, that is, the deformation of the Moho interface. We estimate the Moho change rate in the inland of the TP and find that the Moho interface is suffering an uneven deformation. The Moho is uprising at a rate of 18.1 ± 7.2 mm/year in the west and 21.7 ± 9.7 mm/year in the east of the TP, while there is an obvious deepening rate of −18.3 ± 8.6 mm/year in the central TP. Key Points: A rather poor correlation is found between GRACE observation and hydrological data in the interior basin of the Tibetan PlateauThe GRACE mass rates during the period from 2003 to 2009 have been separated effectivelyThe residual signals in the Tibetan Plateau are explained from the point of view of tectonics [ABSTRACT FROM AUTHOR]

The Groningen gas reservoir, situated in the northeast of the Netherlands is western Europe's largest gas reservoir. Due to gas production measurable subsidence and seismicity has been detected across this region, attributed to the deformations induced by reservoir pore pressure depletion. We investigate the surface displacement history using a principal component analysis‐based inversion method to combine a diverse set of optical leveling, interferometric synthetic aperture radar, and Global Positioning System data to better constrain reservoir compaction and subsidence history. The generated compaction model is then used in combination with prior pressure depletion models to determine a reservoir uniaxial compressibility. The best fitting model of uniaxial compressibility is time independent but spatially variable. The absence of evidence for any significant time delay between changes in depletion and compaction rates supports an instantaneous poroelastic reservoir response. The absence of nonlinear yielding at the largest compaction strains suggests that anelastic deformations are a minor part of reservoir compaction. Key Points: Seismicity is located within the reservoir levelsVariations and changes in gas extraction are not manifested in subsidence dataPressure depletion within reservoir levels is modeled using geodetic inversion [ABSTRACT FROM AUTHOR]

To improve models of ground motion estimation and probabilistic seismic hazard analyses, the engineering seismology field is moving toward developing fully nonergodic ground motion models, models specific for individual source‐to‐site paths. Previous work on this topic has examined systematic variations in ground‐motion along particular paths (from either recorded or simulated earthquake data) and has not included physical properties of the path. We present here a framework to include physical path properties, by seeking correlations between ground motion amplitudes along specific paths and crustal properties, specifically seismic velocity and anelastic attenuation, along that path. Using a large data set of small‐magnitude earthquakes recorded in Southern California, we find a correlation between the gradient of seismic S wave velocity and the path term residual, after accounting for an average geometric spreading and anelastic attenuation, indicating that heterogeneity in crustal velocity primarily controls the path‐specific attenuation. Even in aseismic regions, details of path‐specific ground motion prediction equations can be developed from crustal structure and property data. Key Points: To reduce uncertainty in ground motion (GM) estimation, we present a framework for including crustal properties in empirical GM modelsWe find a relationship between observed GMs and crustal heterogeneity, indicating it dominates regional path effects in Southern CaliforniaWe propose that these path effects are primarily from scattering and show steps forward to scale this framework to larger magnitudes [ABSTRACT FROM AUTHOR]

Taiwan is widely considered to be a typical example of an arc‐continent collision surrounded by two opposite dipping subduction zones. The manner by which the interaction of the two neighboring slabs caused plate collision and mountain building is insufficiently understood. Various hypotheses have been proposed, but the geodynamic feasibility of those remains to be tested. Here we present 3‐D thermomechanical models to study the geodynamic evolution process of a Taiwan‐like setting after an initial transform fault was consumed. In our model setup, the boundary between the Eurasian plate and the South China Sea is northeast trending. The results show that all simulations result in toroidal mantle flow around the slab edges and that slab breakoff as well as a small‐scale mountain belt with high topography and crustal exhumation occurs in most cases. The Eurasian continental crust is exhumed in a dome‐like manner exposing higher‐grade metamorphic rocks, facilitated by high erosion rates and a weak continental lower crust rheology, but inhibited by the presence of a weak arc. A high topography within the orogen, as well as continental slab detachment, can develop for the convergence direction of N307° and large convergence rates. Our modeling results are thus generally consistent with the Eurasian slab‐tearing model proposed for Taiwan based on seismic tomographic studies, and we suggest that the main characteristic features in Taiwan can be explained by the combined effects of fast erosion, a weak lower crust, fast convergence, and a small convergence azimuth. Key Points: We present the first 3‐D thermomechanical geodynamic models to study the geodynamic and plate tectonic evolution of TaiwanFast erosion, fast convergence, and a weak lower crust are the most important mountain‐building ingredientsOur results are consistent with the previously proposed slab‐tearing model to explain the geological formation of Taiwan [ABSTRACT FROM AUTHOR]

The autocorrelation of the seismic transmission response of a layered medium (autocorrelogram), in the presence of a free surface, corresponds to the reflection response. Despite many studies on the imaging of local structures through retrieval and forward modeling of stacked autocorrelograms, there is limited work on the inversion of these data. In this study, we demonstrate that the probabilistic inversion of autocorrelograms is efficient and can be used as an alternative imaging tool when other approaches are not applicable. Here, we calculate autocorrelograms of teleseismic P wave coda recorded on more than 1,200 permanent and temporary seismic stations across Australia and utilize a Bayesian framework to invert these data for crustal imaging. The results show patterns of structures consistent with those seen in previous crustal models constructed from receiver function, seismic reflection, and refraction methods. The new approach can therefore image large‐scale crustal structures comparable to those from other seismological methods. Key Points: We develop a new approach for crustal imaging by utilizing teleseismic P wave coda autocorrelogramsWe retrieve zero‐offset reflections from teleseismic P wave coda to image the crustal structure of Australia through a Bayesian inversionThe results of the probabilistic inversion are consistent with previous crustal models derived from multiple classes of information [ABSTRACT FROM AUTHOR]

Observations from a wintertime and summertime field campaign are used to assess the relationship between black and brown carbon (BC and BrC, respectively) optical properties and particle composition and coating state. The wintertime campaign, in Fresno, CA, was impacted by primary emissions from residential wood burning, secondary organic and inorganic particle formation, and BC from motor vehicles. Two major types of BrC were observed in wintertime. One occurred primarily at night—the result of primary biomass burning emissions. The second was enhanced in daytime and strongly associated with particulate nitrate and the occurrence of fog. The biomass‐burning‐derived BrC absorbed more strongly than the nitrate‐associated BrC but had a weaker wavelength dependence. The wintertime BC‐specific mass absorption coefficient (MACBC) exhibited limited dependence on the ensemble‐average coating‐to‐BC mass ratio (Rcoat‐rBC) at all wavelengths, even up to Rcoat‐rBC of ~5. For the summertime campaign, in Fontana, CA, BC dominated the light absorption, with negligible BrC contribution even after substantial photochemical processing. The summertime MACBC exhibited limited dependence on Rcoat‐rBC, even up to ratios of >10. Based on the four classes of BC‐containing particles identified by Lee et al. (2017, https://doi.org/10.5194/acp‐17‐15055‐2017) for the summertime measurements, the general lack of an absorption enhancement can be partly—although not entirely—attributed to an unequal distribution of coating materials between the BC‐containing particle types. These observations demonstrate that in relatively near‐source environments, even those impacted by strong secondary aerosol production, the ensemble‐average, mixing‐induced absorption enhancement for BC due to coatings can be quite small. Plain Language Summary: Particles in the atmosphere can scatter light, which has a cooling effect, or absorb light, which can contribute to localized atmospheric warming. Black carbon is a highly absorbing yet short‐lived climate pollutant that when coated with other materials can in theory have enhanced absorption. Organic compounds in particles can also absorb light, although tend to absorb less strongly than black carbon. Absorbing organic compounds are collectively referred to as brown carbon. We measured the composition and light absorption properties of atmospheric particles in wintertime Fresno, CA, and summertime Fontana, CA. In Fresno, we found two types of brown carbon contributed significantly to the overall light absorption by particles, in addition to absorption by black carbon. One of the brown carbon aerosol types in Fresno was emitted during wood burning, and the other was produced from chemical reactions in the atmosphere. In summertime Fontana, black carbon particles dominated the light absorption, with little contribution from brown carbon. Overall, at both sites the coating of materials onto black carbon particles had a limited impact on the absorption by black carbon, except to the extent that the materials themselves were absorbing. Key Points: Two co‐located types of ambient brown carbon were characterized, one from biomass combustion and one from secondary aerosol formationLimited mixing‐induced absorption enhancement observed in two distinct environments, despite substantial average coatings on black carbon [ABSTRACT FROM AUTHOR]

The Alcurra Dolerite in the Musgrave Province, central Australia, is part of the c. 1075 Ma Warakurna large igneous province (LIP), which is interpreted to have been emplaced contemporaneously with intracontinental rifting. The Alcurra Dolerite in the eastern Musgrave Province comprises two types of continental tholeiite. Dominant Group 1 dolerites are mainly magnesian tholeiites, whereas subordinate Group 2 dolerites are normal tholeiites. These two groups have distinct chondrite-normalized rare earth element (REE) patterns, primordial mantle-normalized trace element patterns, and incompatible element ratios (e.g. Th/Yb, Nb/Yb, La/Yb and Zr/Y). Both groups are low-Ti and low-Zr, but Group 1 dolerites have higher Ti/Zr (>60) and Ti/Y (>310) values than those of Group 2. Group 1 mainly comprises olivine-microgabbros, and is volumetrically dominant, whereas Group 2 is proportionally minor and includes noritic-microgabbros. Dolerites from both groups plot in discrete fields in 143Nd/144Nd versus 147Sm/144Nd space, along a mixing trend between chondritic or depleted mantle and the c. 1·59 Ga Musgravian basement. Group 1 dolerites have low Rb, Th and K2O contents that preclude their contamination by Musgravian continental crust. They also have incompatible element ratios that overlap with mid-ocean ridge basalt or primitive mantle. Group 2 dolerites have more negative ɛNd values and are also the more incompatible element enriched group; they may have, to some extent, been directly contaminated by Musgravian basement. Low concentrations of light REE (LREE) in Group 1 dolerites indicate a moderate to high percentage of partial melting of a relatively depleted source. Mixing this partial melt with a small proportion of melt derived by a moderate percentage of partial melting of a more incompatible element enriched mantle source could have resulted in the low (La/Sm)N ratios and low absolute La contents seen in these dolerites. Group 1 is divided into two subgroups (1A and 1B) on the basis of LREE abundances and Nb/Yb ratios. These two subgroups may reflect different percentages of partial melting of the depleted source. Petrogenetic interpretations for the Alcurra Dolerite of the eastern Musgrave Province must address published geophysical evidence for asthenospheric mantle upwelling and underplating in the Musgrave Province, and for contemporaneous low- and high-Ti Alcurra Dolerites indicative of a plume to the west where they are associated with Giles Suite layered intrusions. The large proportion of probable asthenosphere-derived melt in the petrogenesis of the Group 1 dolerites from the eastern Musgrave Province indicates either substantial heat transfer, or significant decompression in the mantle. The Warakurna LIP could result from a complex interaction between a plume and mantle upwelling. [ABSTRACT FROM AUTHOR]

Frictional heating, frequently termed Joule heating, results from the difference in ion and neutral flows in the Earth's upper atmosphere and is a major energy sink for the coupled magnetosphere‐ionosphere‐thermosphere system. During disturbed geomagnetic conditions, energy input from the Earth's magnetosphere can strongly enhance ion velocities and densities, which will generally increase the rate of Joule heating. Previous theoretical and experimental studies have shown that small‐scale variations in Joule heating can be quite significant in the overall energy budget. In this study, we employ high‐resolution fitting of ion velocities obtained by Super Dual Auroral Radar Network (SuperDARN) coherent scatter, along with spatially resolved neutral wind data from the Poker Flat Scanning Doppler Imager, to examine the spatial and temporal structure of F region ion temperature enhancements, as well as changes in Joule heating rates due to the neutral wind. These results are compared to those obtained using Poker Flat Incoherent Scatter Radar in order to assess the validity of this analysis, with the objective of developing a method that can be applied to any current or future neutral measurements worldwide, thanks to the global coverage of SuperDARN. We examine the agreement between the ion temperatures predicted using the Scanning Doppler Imager‐SuperDARN method and the temperatures measured directly by Poker Flat Incoherent Scatter Radar and discuss possible reasons for any discrepancies. We observe significant spatial structure in both the ion temperature and Joule heating rates during periods of magnetic activity. Key Points: Ion temperatures are estimated using frictional heating theory with Scanning Doppler Imager and SuperDARN dataThe inclusion of neutral winds has significant effects on Joule heating rates, reducing them during active periodsThis technique allows for 50‐km‐resolution maps of heating rates and temperatures [ABSTRACT FROM AUTHOR]

The propagation of bichromatic wave groups with differences in the wave‐group structure and its influence in long‐wave generation are investigated. The wave‐group structure is controlled by the number of wave groups (Ng) within a repetition period. Consequently, an important energy content is measured at lower frequencies than the group frequency fg, in particular, at the repetition frequency fr. The cross‐shore evolution of the energy at fr is partly explained by nonlinear energy transfers from the primary frequencies and partly by a breakpoint forcing. When Ng increases, the energy transfer to fr during wave group shoaling reduces. When Ng≥3, the amplitude of fr suddenly grows at the breakpoint displaying a node‐antinode pattern within the surf zone. In this case, the observed dominance of the breakpoint forcing over the energy transfers is justified by the combination of steep‐slope regime and steep‐wave conditions. The resultant cross‐shore structure is in agreement with the Symonds et al. (1982, https://doi.org/10.1029/JC087iC01p00492) mechanism. A new methodology is proposed to identify the amplitude and phase cross‐shore evolution of the radiated and reflected components. Due to energy dissipation of short waves and long waves at fg, the swash zone motion can be dominated by wave motions occurring at fr. Plain Language Summary: Examination of the sea surface profile records indicates that wave heights are not uniform showing a tendency of forming wave groups, that is, high waves often seem to be grouped together. During shoreward wave group propagation, the waves forming the groups undergo substantial transformations and they eventually break close to the shoreline, defining a moving wave breakpoint. This moving breakpoint acts as a wave maker generating seaward and shoreward propagating waves whose wavelength is related to the modulation of the wave group (typically long waves). As a result of this long‐wave generation, a characteristic cross‐shore pattern is identified. These breakpoint‐generated long waves have been traditionally measured on field and laboratory under specific conditions associated to relatively steep beach slopes only, with no evidences of their existence on milder beach slopes.The present paper is one of the first investigations on nearshore processes where evidences of breakpoint generated long waves on a mild beach slope (1:100) have been measured. To achieve that, differences in the wave‐group structure have been imposed in the design of the experimental wave cases. Furthermore, a new methodology is proposed to identify and compute the cross‐shore evolution of these breakpoint‐generated long waves. Key Points: The generation and growth of frequency components lower than the group frequency is due to nonlinear energy transfers and breakpoint forcingA new methodology to compute breakpoint‐radiated long waves is presentedBecause of saturation of the short waves and group frequency, the swash dynamics are dominated by lower‐frequency components [ABSTRACT FROM AUTHOR]

We have analyzed the high‐speed video of an upward negative leader that exhibited multiple branches. From the video, which was recorded at a frame rate of 300 kiloframes per second (3.3 μs per frame), we have identified 75 leader steps, 21 being from the leader main channel and 54 from 4 branches of the leader. Through analyzing each individual leader step and branch in detail, we found a similar formation pattern for both the leader step and the branch. This pattern can be described in the following sequence: (1) the streamer area forms ahead of the leader tip, (2) the streamer area and the backward leader channel increase in luminosity, (3) the streamer area and the leader channel decrease in luminosity, (4) the streamer area reilluminates ahead of the leader tip, and (5) the reilluminated streamer area develops to a new leader tip and a new streamer area is emitted forward ahead of the new leader tip. Key Points: The detailed luminosity decrease and reillumination of the leader channel between two consecutive steps are presented for the first timeThe so‐called stem can be the reilluminated streamer which then develops to become a new leader tipLeader steps and branches share a similar formation process [ABSTRACT FROM AUTHOR]

One of the important geological structures that have significant geologic implications on petroleum and gas exploration in the subsurface are listric faults. The classical interpretation of listric faults is usually performed by manual picking, which is not only time consuming and labor intensive but also susceptible to interpreter bias. In this paper, we propose a texture-based interpretation workflow for the automated delineation of major listric faults in a 3D migrated seismic volume. In the first step, we compute three-dimensional gradient of texture (3D-GoT), which describes the texture dissimilarity between neighboring cubes around each voxel in a seismic volume across time or depth, crossline, and inline directions. In the second step, we calculate an adaptive global threshold and apply it to the 3D-GoT map to obtain a binary map, which highlights the probable boundary regions of the listric faults. Finally, we apply post-processing to obtained binary maps that includes morphological opening and curve fitting to yield a delineated listric fault within the migrated seismic volume. The experimental results on a real seismic dataset from the Stratton field in the Texas Gulf coast show the effectiveness of the proposed workflow indicating its great potential for assisting structural interpretation and reservoir characterization in the exploration areas dominated by listric faults as well as the associated rollover anticlines and normal faults. [ABSTRACT FROM AUTHOR]

The use of seismic direct hydrocarbon indicators is very common in exploration and reservoir development to minimise exploration risk and to optimise the location of production wells. DHIs can be enhanced using AVO methods to calculate seismic attributes that approximate relative elastic properties. In this study, we analyse the sensitivity to pore fluid changes of a range of elastic properties by combining rock physics studies and statistical techniques and determine which provide the best basis for DHIs. Gassmann fluid substitution is applied to the well log data and various elastic properties are evaluated by measuring the degree of separation that they achieve between gas sands and wet sands. The method has been applied successfully to well log data from proven reservoirs in three different siliciclastic environments of Cambrian, Jurassic, and Cretaceous ages. We have quantified the sensitivity of various elastic properties such as acoustic and extended elastic (EEI) impedances, elastic moduli ( K and K - μ), lambda-mu-rho method ( λρ and μρ), P-to-S-wave velocity ratio ( V / V ), and Poisson's ratio ( σ) at fully gas/water saturation scenarios. The results are strongly dependent on the local geological settings and our modeling demonstrates that for Cambrian and Cretaceous reservoirs, K - μ, EEI, V / V and σ are more sensitive to pore fluids (gas/water). For the Jurassic reservoir, the sensitivity of all elastic and seismic properties to pore fluid reduces due to high overburden pressure and the resultant low porosity. Fluid indicators are evaluated using two metrics: a fluid indicator coefficient based on a Gaussian model and an overlap coefficient which makes no assumptions about a distribution model. This study will provide a potential way to identify gas sand zones in future exploration. [ABSTRACT FROM AUTHOR]

Air radon concentration measurement is useful for research on geophysical effects, but it is strongly sensitive to site geology and many geophysical and microclimatic processes such as wind, ventilation, air humidity and so on inducing very big fluctuations on the concentration of radon in air. On the contrary, monitoring the radon concentration in soil by measuring the thermal neutron flux reduces environmental effects. In this paper, we report some experimental results on the natural thermal neutron flux as well as on the concentration of air radon and its variations at 4300 m asl. These results were obtained with unshielded thermal neutron scintillation detectors (en-detectors) and radon monitors located inside the ARGO-YBJ experimental hall. The correlation of these variations with the lunar month and 1-year period is undoubtedly confirmed. A method for earthquake prediction provided by a global net of en-detectors is currently under study. [ABSTRACT FROM AUTHOR]

A short, waterborne streamer resistivity survey was conducted on Mono Lake in California. The lake, located on the eastern side of the Sierra Nevada Mountains, contains a significant amount of dissolved solids due to being a terminal lake with no outlet. The survey was conducted to determine if the method could be used to define subbottom sediments and other geological features to answer questions related to recent-past volcanic and tectonic events. The survey used a 15-meter dipole-dipole array towed at approximately 2 mph behind a small flat bottomed boat. The survey was limited in scope to collecting approximately 6,000 m of data within the western cove, where substantial core sampling has taken place. Comparison of the methods indicates the towed array can obtain good quality data despite the lake's conductivity being in excess of 84,000 uS/cm. The resistivity models reconstructed geological material upwards of 400 ohm-m to depths of 35 m, which likely represent hard rock below the lake. We conclude that the method could be used to map most of the shallow areas of the lake, where the water column is less than 20 m. The deepest areas of the lake, south of Paoha Island, would require streamer resistivity cables with an electrode spacing of at least 60 m. [ABSTRACT FROM AUTHOR]

We have tested the Vertical-Array Differential Target Antenna Coupling (DTAC) system over a variety of well-characterized, buried targets. The DTAC system produces a primary field in the frequency range of 10 Hz to 10 kHz and records secondary magnetic fields from subsurface targets, relative to a reference frequency. The current DTAC system has higher power, compared with our earlier tests, and this system is suitable for either ground or airborne mapping of a wide variety of near-surface targets, which might be encountered in civil engineering, water resources, environmental characterization, mining, and other natural-resource exploration. Profiles over three well-characterized targets show a close agreement between the measured DTAC response and model simulations. Conventional field measurements using induced magnetic fields are also displayed and they do not show nearly as effective mapping of the targets. Another profile shows that the DTAC method has greatly reduced sensitivity to surface clutter, compared to conventional measurements. [ABSTRACT FROM AUTHOR]

The paper considers Poisson temporal occurrence of earthquakes and presents a way to integrate uncertainties of the estimates of mean activity rate and magnitude cumulative distribution function in the interval estimation of the most widely used seismic hazard functions, such as the exceedance probability and the mean return period. The proposed algorithm can be used either when the Gutenberg-Richter model of magnitude distribution is accepted or when the nonparametric estimation is in use. When the Gutenberg-Richter model of magnitude distribution is used the interval estimation of its parameters is based on the asymptotic normality of the maximum likelihood estimator. When the nonparametric kernel estimation of magnitude distribution is used, we propose the iterated bias corrected and accelerated method for interval estimation based on the smoothed bootstrap and second-order bootstrap samples. The changes resulted from the integrated approach in the interval estimation of the seismic hazard functions with respect to the approach, which neglects the uncertainty of the mean activity rate estimates have been studied using Monte Carlo simulations and two real dataset examples. The results indicate that the uncertainty of mean activity rate affects significantly the interval estimates of hazard functions only when the product of activity rate and the time period, for which the hazard is estimated, is no more than 5.0. When this product becomes greater than 5.0, the impact of the uncertainty of cumulative distribution function of magnitude dominates the impact of the uncertainty of mean activity rate in the aggregated uncertainty of the hazard functions. Following, the interval estimates with and without inclusion of the uncertainty of mean activity rate converge. The presented algorithm is generic and can be applied also to capture the propagation of uncertainty of estimates, which are parameters of a multiparameter function, onto this function. [ABSTRACT FROM AUTHOR]

We performed three-dimensional density modeling of Showa-Shinzan lava dome, Usu, Japan, by joint inversion of the gravity anomaly and recently obtained muon radiography data. Our multilayer emulsion muon detector significantly reduces the background noise in our measurements of the muon flux through the dome. The high-quality muon data enables us to more accurately reconstruct the density structure of the lava dome compared with our own previous work. We find that the lava dome consists of a cylindrical column of massive lava with a diameter of 300 m, and that there is no evidence of magma intrusion in the shallow part of the plateau, located east of the dome. [ABSTRACT FROM AUTHOR]

Groundwater extraction is one of the most typical disturbance factors for strain observation in seismic precursor monitoring. The statistic regression method is used to study based on the relation between the variation of strain and the groundwater level. The least square regression linear model is built between the annual variation of Sangzi groundwater level and the Xiaoxinzhuang strain data. Such model meets t test with significance level $$\alpha = 0. 0 5$$ , which confirms that groundwater-level change in each year affects strain measurement significantly and strain's trend variation is related to groundwater-level change. Consequently, a new correction method about strain data is put forward based on the groundwater-level annual variation to eliminate the trend change. Results indicate that the accumulated residual deformation causes the horizontal displacement and strain change, which is on account of that the amount of groundwater recharge is less than that of extraction around Xiaoxinzhuang cave, the phreatic surface continues to descend, and residual deformation accumulates and leads to local subsidence area. Therefore, the decline trend change of strain is related to groundwater-level change and is not seismic precursor. [ABSTRACT FROM AUTHOR]

Anomalies in polarization angles of teleseismic waves have been used to understand effect of scattered arrivals from subsurface heterogeneities. Seismological data recorded in southern India show polarization anomalies up to 5° for several stations. These anomalies are most pronounced for earthquakes from western and southern azimuths. Furthermore, stations located near the boundary of Dharwar craton and southern Granulites are more affected by scattered waves. Considering that many of the nearby stations show similar patterns of polarization anomalies, it is likely that the source of scattered energy is located at shallower depths. The non-stationary nature of seismic arrivals warrants determination of frequency-dependent polarization. Result obtained using multi-taper spectral analysis method indicates that data are contaminated at frequencies greater than ~2 Hz for most of the stations. Furthermore, surface-wave records also indicate off-azimuth arrivals, and quasi-Love waves indicating heterogeneities or anisotropy in the subsurface. These small-scale heterogeneities that may be located in crust may be important for studies using converted phases and ground motion prediction studies. [ABSTRACT FROM AUTHOR]

Huoqiu iron deposit is a typical Precambrian banded iron-formation (BIF) field which is located in the North China Craton (NCC). To detect the deep ore bodies around Dawangzhuang Village in Yingshang County, north of the Huoqiu deposit field, electromagnetic methods were tested. As the ore bodies are buried under very thick conductive Quaternary sediments, the use of EM methods is a great challenge. Short-offset transient electromagnetic method (SOTEM) was applied in the area as we wanted to test due to its detection depth and resolution. A 2D model was first built according to the geology information and magnetic measurement results. Then, 2D forward and 1D inversion were carried out using FDTD and Occam's algorithm, respectively. The synthetic modeling results helped us with the survey design and interpretation. Two 1400-m-long survey lines with offset of 500 and 1000 m were laid perpendicular to the BIF's strike, and the transmitting parameters were selected by a test measurement at the vicinity of a local village. Finally, the structure of survey area and BIF bodies were determined based on the 1D inversion results of real data, and showed a consistency with the subsequent drill results. Our application of SOTEM in detecting hidden BIF buried under very thick conductive layer has shown that the method is capable of penetrating great depth more than 1000 m even in a very conductive environment and will be an effective tool for deep resources investigation. [ABSTRACT FROM AUTHOR]

Full waveform inversion (FWI) can be applied to obtain an accurate velocity model that contains important geophysical and geological information. FWI suffers from the local minimum problem when the starting model is not sufficiently close to the true model. Therefore, an accurate macroscale velocity model is essential for successful FWI, and Laplace-Fourier-domain FWI is appropriate for obtaining such a velocity model. However, conventional Laplace-Fourier-domain FWI remains an ill-posed and ill-conditioned problem, meaning that small errors in the data can result in large differences in the inverted model. This approach also suffers from certain limitations related to the logarithmic objective function. To overcome the limitations of conventional Laplace-Fourier-domain FWI, we introduce a weighted l objective function, instead of the logarithmic objective function, as the data-domain objective function, and we also introduce two different model-domain regularizations: first-order Tikhonov regularization and prior model regularization. The weighting matrix for the data-domain objective function is constructed to suitably enhance the far-offset information. Tikhonov regularization smoothes the gradient, and prior model regularization allows reliable prior information to be taken into account. Two hyperparameters are obtained through trial and error and used to control the trade-off and achieve an appropriate balance between the data-domain and model-domain gradients. The application of the proposed regularizations facilitates finding a unique solution via FWI, and the weighted l objective function ensures a more reasonable residual, thereby improving the stability of the gradient calculation. Numerical tests performed using the Marmousi synthetic dataset show that the use of the weighted l objective function and the model-domain regularizations significantly improves the Laplace-Fourier-domain FWI. Because the Laplace-Fourier-domain FWI is improved, the frequency-domain FWI, in which the Laplace-Fourier-domain FWI result is used as the starting model, yields inversion result much closer to the true velocity. [ABSTRACT FROM AUTHOR]

Surface wave tomography based on continuous regionalization of model parameters is widely used to invert for 2-D phase or group velocity maps. An inevitable problem is that the distribution of ray paths is far from homogeneous due to the spatially uneven distribution of stations and seismic events, which often affects the spatial resolution of the tomographic model. We present an improved tomographic method with a spatially varying smoothing scheme that is based on the continuous regionalization approach. The smoothness of the inverted model is constrained by the Gaussian a priori model covariance function with spatially varying correlation lengths based on ray path density. In addition, a two-step inversion procedure is used to suppress the effects of data outliers on tomographic models. Both synthetic and real data are used to evaluate this newly developed tomographic algorithm. In the synthetic tests, when the contrived model has different scales of anomalies but with uneven ray path distribution, we compare the performance of our spatially varying smoothing method with the traditional inversion method, and show that the new method is capable of improving the recovery in regions of dense ray sampling. For real data applications, the resulting phase velocity maps of Rayleigh waves in SE Tibet produced using the spatially varying smoothing method show similar features to the results with the traditional method. However, the new results contain more detailed structures and appears to better resolve the amplitude of anomalies. From both synthetic and real data tests we demonstrate that our new approach is useful to achieve spatially varying resolution when used in regions with heterogeneous ray path distribution. [ABSTRACT FROM AUTHOR]

Tests aimed to verify whether there is a correlation between the basic parameters characterizing the mechanical properties of rocks with the properties of ionizing radiation scattered by rocks were performed as part of the research. The positive correlation between the two examined properties would provide the basis for the development of a new method of rock testing using radiation sources or devices generating ionizing radiation. The method could be applied to carry out research in underground boreholes to determine the mechanical properties of the rock mass in situ. The study allowed the verification of the adopted assumptions for the proposed method. The verification was based on the correlation analysis of absorption coefficients of the ionizing radiation of rocks from the Upper Silesian Coal Basin with the results of the research on mechanical and physical properties. [ABSTRACT FROM AUTHOR]

The electrical conductivity of pyroxene andesite was in situ measured under conditions of 1.0-2.0 GPa and 673-1073 K using a YJ-3000t multi-anvil press and Solartron-1260 Impedance/Gain-phase analyzer. Experimental results indicate that the electrical conductivities of pyroxene andesite increase with increasing temperature, and the electrical conductivities decrease with the rise of pressure, and the relationship between electrical conductivity ( σ) and temperature ( T) conforms to an Arrhenius relation within a given pressure and temperature range. When temperature rises up to 873-923 K, the electrical conductivities of pyroxene andesite abruptly increase, and the activation enthalpy increases at this range, which demonstrates that pyroxene andesite starts to dehydrate. By the virtue of the activation enthalpy (0.35-0.42 eV) and the activation volume (−6.75 ± 1.67 cm/mole) which characterizes the electrical properties of sample after dehydration, we consider that the conduction mechanism is the small polaron conduction before and after dehydration, and that the rise of carrier concentration is the most important reason of increased electrical conductivity. [ABSTRACT FROM AUTHOR]

The problem of estimating the maximum possible earthquake magnitude $$m_\mathrm{max}$$ has attracted growing attention in recent years. Due to sparse data, the role of uncertainties becomes crucial. In this work, we determine the uncertainties related to the maximum magnitude in terms of confidence intervals. Using an earthquake catalog of Iran, $$m_\mathrm{max}$$ is estimated for different predefined levels of confidence in six seismotectonic zones. Assuming the doubly truncated Gutenberg-Richter distribution as a statistical model for earthquake magnitudes, confidence intervals for the maximum possible magnitude of earthquakes are calculated in each zone. While the lower limit of the confidence interval is the magnitude of the maximum observed event,the upper limit is calculated from the catalog and the statistical model. For this aim, we use the original catalog which no declustering methods applied on as well as a declustered version of the catalog. Based on the study by Holschneider et al. (Bull Seismol Soc Am 101(4):1649-1659, 2011), the confidence interval for $$m_\mathrm{max}$$ is frequently unbounded, especially if high levels of confidence are required. In this case, no information is gained from the data. Therefore, we elaborate for which settings finite confidence levels are obtained. In this work, Iran is divided into six seismotectonic zones, namely Alborz, Azerbaijan, Zagros, Makran, Kopet Dagh, Central Iran. Although calculations of the confidence interval in Central Iran and Zagros seismotectonic zones are relatively acceptable for meaningful levels of confidence, results in Kopet Dagh, Alborz, Azerbaijan and Makran are not that much promising. The results indicate that estimating $$m_\mathrm{max}$$ from an earthquake catalog for reasonable levels of confidence alone is almost impossible. [ABSTRACT FROM AUTHOR]