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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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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 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]

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]

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]

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]

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]

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]

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]

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]

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]

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 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]

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]

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]

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]

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]

The marker-in-cell method is generally considered a flexible and robust method to model the advection of heterogenous non-diffusive properties (i.e., rock type or composition) in geodynamic problems. In this method, Lagrangian points carrying compositional information are advected with the ambient velocity field on an Eulerian grid. However, velocity interpolation from grid points to marker locations is often performed without considering the divergence of the velocity field at the interpolated locations (i.e., non-conservative). Such interpolation schemes can induce non-physical clustering of markers when strong velocity gradients are present (Journal of Computational Physics 166:218-252, 2001) and this may, eventually, result in empty grid cells, a serious numerical violation of the marker-in-cell method. To remedy this at low computational costs, Jenny et al. (Journal of Computational Physics 166:218-252, 2001) and Meyer and Jenny (Proceedings in Applied Mathematics and Mechanics 4:466-467, 2004) proposed a simple, conservative velocity interpolation scheme for 2-D staggered grid, while Wang et al. (Geochemistry, Geophysics, Geosystems 16(6):2015-2023, 2015) extended the formulation to 3-D finite element methods. Here, we adapt this formulation for 3-D staggered grids (correction interpolation) and we report on the quality of various velocity interpolation methods for 2-D and 3-D staggered grids. We test the interpolation schemes in combination with different advection schemes on incompressible Stokes problems with strong velocity gradients, which are discretized using a finite difference method. Our results suggest that a conservative formulation reduces the dispersion and clustering of markers, minimizing the need of unphysical marker control in geodynamic models. [ABSTRACT FROM AUTHOR]

We use historical and recent major earthquakes and GPS geodetic data to compute seismic strain rate, geodetic slip deficit, static stress drop, the parameters of the magnitude-frequency distribution and geodetic strain rate in the Iranian Plateau to identify seismically mature fault segments and regions. Our analysis suggests that 11 fault segments are in the mature stage of the earthquake cycle, with the possibility of generating major earthquakes. These faults primarily are located in the north and the east of Iran. Four seismically mature regions in southern Iran with the potential for damaging strong earthquakes are also identified. We also delineate four additional fault segments in Iran that can generate major earthquakes without robust clues to their maturity.The most important fault segment in this study is the strike-slip system near the capital city of Tehran, with the potential to cause more than one million fatalities. [ABSTRACT FROM AUTHOR]

The paper describes the complex of scientific instruments and the algorithm of the 'Molniya-Gamma' experiment on measuring gamma-ray fluxes in the energy range of 32-750 keV carried out in 2011 on board the Russian Segment (RS) of the International Space Station (ISS). About 500 thousand energy spectra with a time resolution of 1 min were obtained in 512 energy channels during 232 days. One-second variations in the number of gamma quanta in four energy channels and the triggered fluxes of gamma quanta lasting less than 100 ms were recorded simultaneously. The data obtained allow us to study temporal and spatial variation of gamma-ray radiation to detect terrestrial gamma flashes (TGFs). Data on very large number of gamma-ray spikes were acquired through a trigger data mode with a low threshold. [ABSTRACT FROM AUTHOR]

The upper part of the crust shows generally brittle behaviour while deeper zones, including the mantle, may present ductile behaviour, depending on the pressure-temperature conditions; moreover, some parts are melted. Seismic waves can be used to detect these conditions on the basis of reflection and transmission events. Basically, from the elastic-plastic point of view the seismic properties (seismic velocity and density) depend on effective pressure and temperature. Confining and pore pressures have opposite effects on these properties, such that very small effective pressures (the presence of overpressured fluids) may substantially decrease the P- and S-wave velocities, mainly the latter, by opening of cracks and weakening of grain contacts. Similarly, high temperatures induce the same effect by partial melting. To model these effects, we consider a poro-viscoelastic model based on Gassmann equations and Burgers mechanical model to represent the properties of the rock frame and describe ductility in which deformation takes place by shear plastic flow. The Burgers elements allow us to model the effects of seismic attenuation, velocity dispersion and steady-state creep flow, respectively. The stiffness components of the brittle and ductile media depend on stress and temperature through the shear viscosity, which is obtained by the Arrhenius equation and the octahedral stress criterion. Effective pressure effects are taken into account in the dry-rock moduli using exponential functions whose parameters are obtained by fitting experimental data as a function of confining pressure. Since fluid effects are important, the density and bulk modulus of the saturating fluids (water and steam) are modeled using the equations provided by the NIST website, including supercritical behaviour. The theory allows us to obtain the phase velocity and quality factor as a function of depth and geological pressure and temperature as well as time frequency. We then obtain the PS and SH equations of motion recast in the velocity-stress formulation, including memory variables to avoid the computation of time convolutions. The equations correspond to isotropic anelastic and inhomogeneous media and are solved by a direct grid method based on the Runge-Kutta time stepping technique and the Fourier pseudospectral method. The algorithm is tested with success against known analytical solutions for different shear viscosities. An example shows how anomalous conditions of pressure and temperature can in principle be detected with seismic waves. [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]

This study delineates the relative performance of the 12-km resolution NCMRWF regional Unified Model (NCUM-R) over the operational global NCUM (NCUM-G) model. Forecasts of four Bay of Bengal (BoB) landfalling tropical cyclones (TCs) using several different initial conditions (ICs) are used to compare the performance of two models. The position and intensity errors of the TCs are estimated with respect to the India Meteorological Department (IMD) and Joint Typhoon Warning Center (JTWC) best-track datasets and an inter-comparison study is also carried out between IMD and JTWC. The overall results suggest that the NCUM-R simulates the position and intensity of TCs more accurately compared to the NCUM-G. A majority of the TC tracks in the NCUM-G diverge more from the IMD track when compared to NCUM-R simulated tracks. It is also clearly noticed that both the models are more skillful in track prediction when initialized at intensity stages greater than 'cyclone' category. However, the mean position errors at different forecast hours and landfall errors of TCs are reduced by approximately 31 and 47% in the NCUM-R simulations compared to NCUM-G simulations, respectively. The mean gain in skill of the NCUM-R in cross track (CT) and along track (AT) error is around 29 and 24% over NCUM-G, respectively. The intensity errors are less in the NCUM-R simulations. The mean rainfall skill scores are considerably improved in the NCUM-R simulations in day-1 and day-2 as compared to the NCUM-G simulations. It is noticed that the mean position errors of the TCs are approximately 8% lower when compared against the JTWC tracks than the IMD tracks. However, the intensity errors are higher against the JTWC than that of IMD most likely due to the averaging period of the wind speed. [ABSTRACT FROM AUTHOR]

We study the uppermost mantle velocities and dip of Indian Moho beneath the NW Himalaya and Ladakh using 42 regional waveform data recorded on 15 seismographs along a ~600 km-long profile. We use the two-way travel time and interstation velocity methods. The apparent Pn and Sn velocities beneath the NW Himalaya are 8.08 ± 0.04 and 4.64 ± 0.07 km/s for earthquakes occurring south of the profile (downdip, western Indian shield) and 8.70 ± 0.13 and 4.76 ± 0.12 km/s for earthquakes from north (updip, western Tibet). Similarly, these velocities beneath Ladakh are 7.18 ± 0.07 and 4.32 ± 0.05 km/s for earthquakes due south (downdip, north Indian shield) and 8.50 ± 0.10 and 4.39 ± 0.12 km/s for earthquakes due north (updip, western Tibet). These velocity variations constrain the Moho dip at ~2.4 ± 0.14º beneath the NW Himalaya and ~6.6 ± 0.54º beneath Ladakh. Considering the varying dips along the profile, we observe that the true Pn (8.37 ± 0.07 km/s) and Sn (4.70 ± 0.1 km/s) velocities are higher for the NW Himalaya than for Ladakh (7.73 ± 0.08 and 4.33 ± 0.09 km/s). The large variation in interstation Pn velocity is observed between the station pairs near the Indus Zangpo Suture zone due to steep dipping (~7.1º to 6.26º) of the Indian Moho. In the Himalaya region, the interstation and average values of the velocities and Moho dip are comparable, whereas a variation is observed in different segments of the Ladakh region. The results show that the Indian Moho is underthrusting at a shallow angle (~2.5º) beneath the Himalaya, steepens abruptly (~6.6º) further north of the Southern Tibetan Detachment and continues at a shallow angle (~3.8º) beneath Ladakh. [ABSTRACT FROM AUTHOR]

In this study, we discuss the adjustment of grid definition in relation to seismic tomography in the case of elliptical anisotropic media. To optimize cell numbers and dimensions, the results of a staggered grid method are used to define an adjusted grid as a starting model for inversion. This procedure can be iterated, although improvements are not assured. First, two synthetic models with growing level of complexity are performed. Next, data from a previously conducted field survey are analyzed by introducing staggered grids. Finally, the results are compared with the previous results. The adjusted grid represents a technique that can be used to obtain an effective way of discretizing the model domain for further inversion, which often improves results for the velocity model. These conclusions can also be applied to isotropic media, as described in this study. [ABSTRACT FROM AUTHOR]

Four gridding methods for GPS velocities are compared in terms of their precision, applicability and robustness by analyzing simulated data with uncertainties from 0.0 to ±3.0 mm/a. When the input data are 1° × 1° grid sampled and the uncertainty of the additional error is greater than ±1.0 mm/a, the gridding results show that the least-squares collocation method is highly robust while the robustness of the Kriging method is low. In contrast, the spherical harmonics and the multi-surface function are moderately robust, and the regional singular values for the multi-surface function method and the edge effects for the spherical harmonics method become more significant with increasing uncertainty of the input data. When the input data (with additional errors of ±2.0 mm/a) are decimated by 50% from the 1° × 1° grid data and then erased in three 6° × 12° regions, the gridding results in these three regions indicate that the least-squares collocation and the spherical harmonics methods have good performances, while the multi-surface function and the Kriging methods may lead to singular values. The gridding techniques are also applied to GPS horizontal velocities with an average error of ±0.8 mm/a over the Chinese mainland and the surrounding areas, and the results show that the least-squares collocation method has the best performance, followed by the Kriging and multi-surface function methods. Furthermore, the edge effects of the spherical harmonics method are significantly affected by the sparseness and geometric distribution of the input data. In general, the least-squares collocation method is superior in terms of its robustness, edge effect, error distribution and stability, while the other methods have several positive features. [ABSTRACT FROM AUTHOR]

Up to now, several methods have been proposed to determine the mode I fracture toughness of rocks. In this research, different cylindrical and disc shape samples, namely: chevron bend (CB), short rod (SR), cracked chevron notched Brazilian disc (CCNBD), and semi-circular bend (SCB) specimens were considered for investigating mode I fracture behavior of a marble rock. It is shown experimentally that the fracture toughness values of the tested rock material obtained from different test specimens are not consistent. Indeed, depending on the geometry and loading type of the specimen, noticeable discrepancies can be observed for the fracture toughness of a same rock material. The difference between the experimental mode I fracture resistance results is related to the magnitude and sign of T-stress that is dependent on the geometry and loading configuration of the specimen. For the chevron-notched samples, the critical value of T-stress corresponding to the critical crack length was determined using the finite element method. The CCNBD and SR specimens had the most negative and positive T-stress values, respectively. The dependency of mode I fracture resistance to the T-stress was shown using the extended maximum tangential strain (EMTSN) criterion and the obtained experimental rock fracture toughness data were predicted successfully with this criterion. [ABSTRACT FROM AUTHOR]

Machine learning techniques such as Gaussian Processes can be used to identify stratigraphically important features in geophysical logs. The marker shales in the banded iron formation hosted iron ore deposits of the Hamersley Ranges, Western Australia, form distinctive signatures in the natural gamma logs. The identification of these marker shales is important for stratigraphic identification of unit boundaries for the geological modelling of the deposit. Machine learning techniques each have different unique properties that will impact the results. For Gaussian Processes (GPs), the output values are inclined towards the mean value, particularly when there is not sufficient information in the library. The impact that these inclinations have on the classification can vary depending on the parameter values selected by the user. Therefore, when applying machine learning techniques, care must be taken to fit the technique to the problem correctly. This study focuses on optimising the settings and choices for training a GPs system to identify a specific marker shale. We show that the final results converge even when different, but equally valid starting libraries are used for the training. To analyse the impact on feature identification, GP models were trained so that the output was inclined towards a positive, neutral or negative output. For this type of classification, the best results were when the pull was towards a negative output. We also show that the GP output can be adjusted by using a standard deviation coefficient that changes the balance between certainty and accuracy in the results. [ABSTRACT FROM AUTHOR]

In the linearized seismic full waveform inversion (FWI), it is well known that a good initial model is needed to avoid cycle-skipping issue, especially when the low-frequency components of data are lacking. To solve the problem, we develop a joint first-arrival traveltime and early arrival envelope inversion method (JTE) to build a good near-surface velocity model with low-wavenumber components. The JTE method combines the robustness of nonlinear traveltime inversion and the low-frequency information embedded in the waveform envelope. In two synthetic experiments, we confirm that traveltime inversion constrains the top near-surface velocity structures tightly, while the envelope inversion recovers the low-wavenumber structures with low-velocity objects or layers. Using the results of JTE as starting models, we find that FWI can produce accurate solutions for complex numerical models. In a real-data example, JTE followed by FWI resolves a near-surface velocity model to improve statics corrections for the subsurface stacking image. [ABSTRACT FROM AUTHOR]

Geophysical prospecting of underground caves being performed on a construction site is often still a challenging procedure. Estimation of a likelihood level of an anomaly found is frequently a mandatory requirement of a project principal due to necessity of risk/safety assessment. However, the methodology of such estimation is not hitherto developed. Aiming to put forward such a methodology the present study (being performed as a part of an underground caves mapping prior to the land development on the site area) consisted of application of electrical resistivity tomography (ERT) together with statistical analysis utilized for the likelihood assessment of underground anomalies located. The methodology was first verified via a synthetic modeling technique and applied to the in situ collected ERT data and then crossed referenced with intrusive investigations (excavation and drilling) for the data verification. The drilling/excavation results showed that the proper discovering of underground caves can be done if anomaly probability level is not lower than 90 %. Such a probability value was shown to be consistent with the modeling results. More than 30 underground cavities were discovered on the site utilizing the methodology. [ABSTRACT FROM AUTHOR]

A potential head ward retreat landslide area was identified in Munnar, a hill station in Western Ghats of Kerala, India. This imminent landslide was suspected to be formed in three different stages viz., evolution of plateau region, upliftment of the plateau region and the consequent slope modification which ultimately facilitated landslide occurrence. Geophysical study through vertical electrical sounding reveals that more than 11 m thick soil is still left in an overhanging position in the crown portion of the landslide and the thickness continues to the top of that ridge. In the event of high rainfall, the land can fail as there is no toe support, and the slope angle is >40º. This area is adjacent to a college building and in the event of any further landslide, the consequence will be high. Slope stability analysis using one-dimensional infinite slope stability model reveals that the entire area occupied by the college and the adjacent areas are unstable even in dry conditions. Rainfall threshold analysis shows that the landslide occurred due to very high amount of a 5-day antecedent rainfall rather than a daily rainfall during the monsoon. All these point towards a pressing requirement of landslide management practices in this area. This study also attempts to suggest a few management practices to minimize the effect of landslides. [ABSTRACT FROM AUTHOR]

Within the frame of the International DORIS Service (IDS), the CNES/CLS Analysis Center contributes to the geodetic and geophysical research activity through DORIS data analysis. A strategy was developed for the processing of the measurements of the DGXX instruments in RINEX/DORIS format, as it will be the only type of DORIS format made available by CNES, starting with the Jason-3 and Sentinel-3A missions launched at the beginning of the year 2016. The purpose of this paper is to describe the method implemented in the CNES/CLS Analysis Center orbit computation software GINS to process RINEX/DORIS data files. Phase measurements are converted into Doppler counts and then into relative satellite-to-beacon velocities. In this approach, the iono-free phase centers have to be used as the end points of the measurement instead of the 2 GHz phase centers. Given that, the processing results with RINEX/DORIS data are similar to the ones obtained with the usual doris2.2 data, except the scale factor of the Terrestrial Reference Frame in the 7-parameter transform of the network solution. We also address the issue of the scale factor increase from 2012 observed by all the IDS Analysis Centers in their solutions for the ITRF2014 combination. We show that the scale increase in 2012 is dependent on the type of DORIS data used. This scale increase is also enhanced by a bias due to the inclusion of HY-2A data, but which can be eliminated by adopting different coordinates of the onboard DORIS antenna phase center. [ABSTRACT FROM AUTHOR]

Within the frame of the International DORIS Service, the CNES/CLS Analysis Center, previously known as LCA and renamed GRG, contributes to the geodetic and geophysical research activity through DORIS data analysis. The main work carried out in the past two years concerns the processing of the measurements collected by the DORIS-equipped satellites over 22 years, in order to provide a homogeneous series of station coordinates and Earth pole parameters for the IDS contribution to the ITRF2014. First, we brought several upgrades to the processing and the modeling. Some of them are corrective actions to issues raised during or shortly after the production of our contribution to the ITRF2008 (ground station frequency offsets, attitude laws and macromodels). Recent models have been assessed with the aim to update our analysis configuration. Among others, we adopted the time variable gravity (TVG) model EIGEN-6S2 and applied tropospheric gradients. Then we processed almost all the DORIS data collected between January 1993 and December 2014. The series of weekly SINEX solutions derived from this processing is labeled grgwd40. This new series performs better than the series produced for ITRF2008. Especially, the results discussed in this paper show a decrease of 2% of the DORIS orbit residuals as well as a strong reduction of the annual terms of the TRF scale and Tz translation which can be explained by the application of the TVG model. [ABSTRACT FROM AUTHOR]

The Cadzow rank-reduction method can be effectively utilized in simultaneously denoising and reconstructing 5-D seismic data that depend on four spatial dimensions. The classic version of Cadzow rank-reduction method arranges the 4-D spatial data into a level-four block Hankel/Toeplitz matrix and then applies truncated singular value decomposition (TSVD) for rank reduction. When the observed data are extremely noisy, which is often the feature of real seismic data, traditional TSVD cannot be adequate for attenuating the noise and reconstructing the signals. The reconstructed data tend to contain a significant amount of residual noise using the traditional TSVD method, which can be explained by the fact that the reconstructed data space is a mixture of both signal subspace and noise subspace. In order to better decompose the block Hankel matrix into signal and noise components, we introduced a damping operator into the traditional TSVD formula, whichwe call the damped rank-reduction method. The damped rank-reduction method can obtain a perfect reconstruction performance even when the observed data have extremely low signal-to-noise ratio. The feasibility of the improved 5-D seismic data reconstruction method was validated via both 5-D synthetic and field data examples. We presented comprehensive analysis of the data examples and obtained valuable experience and guidelines in better utilizing the proposed method in practice. Since the proposed method is convenient to implement and can achieve immediate improvement, we suggest its wide application in the industry. [ABSTRACT FROM AUTHOR]