Geophysical Journal International

SummaryThe rigidity and intraplate deformation of the Indian plate has long been a subject of debate. To understand the present-day intraplate deformation, we utilized data from 34 well-distributed continuous Global Positioning System (cGPS) stations across the stable part of the Indian subcontinent to derive refined Euler pole parameters (51.834° ± 0.0495° N,3.9708° ± 0.9351° E, Ω = 0.52067° ± 0.002684°/Myr) and establish an updated Indian Reference Frame (IRF). The intraplate velocity field suggests a westward motion of the Northern Tectonic Block (NTB) (up to 2.5 mm/yr) relative to the stable Southern Tectonic Block (STB) (≤1 mm/yr) along the Narmada-Son Lineament (NSL) in the Central Indian Tectonic Zone (CITZ). The rotation pattern inferred from strain analysis also exhibits a progressive increase in the anticlockwise rotation from the STB (~2 nrad/yr) to NTB (~6 nrad/yr). Thus, the subtle, yet systematic variation in the intraplate deformation pattern from STB to NTB across the NSL strengthen the non-rigid behaviour of the Indian sub-continent and reflects its accommodation of far-field plate boundary forces generated by the Indo-Eurasian collision in the Himalayan region. To further substantiate these findings, we propose to conduct advanced investigations using a denser network of cGPS stations over the Indian subcontinent.

SummaryUncertainty quantification is indispensable for reliable magnetotelluric (MT) data interpretation, given the inherent non-uniqueness of MT inverse problem solutions. However, traditional sampling-based probabilistic schemes often require millions of costly forward predictions, making them computationally prohibitive. To address this, we develop a trans-dimensional Bayesian inversion framework that incorporates a novel forward modelling operator and a reversible-jump Markov chain Monte Carlo (RJMCMC) algorithm for robust uncertainty quantification. The forward modeling method leverages the extended Fourier DeepONet (EFDO) network. Once trained, the EFDO achieves up to a 300-fold acceleration in forward predictions compared to a conventional Finite Volume (FV)-based solver. Furthermore, we utilize an adaptive Delaunay model parameterization during the sampling process to allow for efficient model space exploration. We demonstrate the efficacy of the proposed approach through numerical experiments and application to the COPROD2 MT field dataset. Overall, this work advances Bayesian MT inversion by enabling rapid, high-dimensional inference of subsurface electrical resistivity structures, thereby facilitating reliable geological interpretation.

SummaryDistributed Acoustic Sensing (DAS) has emerged as a valuable complement to conventional seismic monitoring techniques. By converting fiber-optic cables into dense arrays of virtual sensors, DAS enables the application of standard large-array processing methods. However, its directional sensitivity—limited to strain measurements along the fiber axis—may restrict its potential for full wavefield analysis. To address this limitation, we investigate the capabilities of DAS on a fiber-optic cable installed both horizontally, near the surface, and vertically, in a borehole, thereby creating a so-called 3D-DAS array. The survey was carried out in the southern Munich region (Germany) to monitor local seismicity associated with nearby deep geothermal operations. In this study, we present the data acquisition setup and describe a processing workflow developed to characterize source and wavefield parameters of seismic events from DAS recordings. The workflow is illustrated using a nearby ${{M}_w}$ = 0.48 seismic event. Taking advantage of the configuration of the fiber optic cable, we demonstrate that the 3D-DAS array enables estimation of the wavefield back-azimuth, incidence angle and slowness, and compare these results with those provided by a local network of seismometers. In addition, seismic source parameters, including seismic moment and stress drop, are estimated from DAS data acquired in the 250-meter-deep vertical well. These parameters are derived after converting strain-rate to ground motion, a process quantitatively validated using a co-located three-component broadband seismometer. The results and waveform evaluation demonstrate that the 3D-DAS array provides reliable and comprehensive measurements, independently of the existing local seismic network.

SummaryIn many fields of geoscience, researchers study the Earth’s properties by solving inverse or inference problems. Probabilistic approaches have gained increased attention over the past decade because they address the non-linearity and non-uniqueness properties of many naturally-inspired inverse problems and allow uncertainties in the solutions to be estimated. However, implementing such methods is computationally expensive and requires expertise in inverse and inference theory, high performance computing, and the geoscientific theory to be inverted. This makes the methods inaccessible to many geoscientists. In this paper, we first review the theoretical background of a particular suite of probabilistic algorithms referred to as parametric variational inference (PVI), and introduce GeoPVI, an open-source Python package designed to facilitate the implementation of these methods. With GeoPVI, users can model uncertainties in their geophysical parameter estimates efficiently given their expertise in inverse theory. It differs from sampling-based, non-parametric variational methods in that the probabilistic solution – the posterior or post-inversion probability distribution function that describes uncertainty in the model parameters of interest – is parametrised by explicit mathematical expressions. These expressions allow for the efficient storage and transfer, and for the evaluation of the posterior probability density for any set of parameter values. We demonstrate how to use the package to solve a set of problems, including tomographic imaging using travel time data, full waveform inversion, surface wave dispersion inversion, and vertical electrical sounding. We provide built-in forward functions to simulate first arrival travel times and full acoustic waveform data (in two spatial dimensions), and external forward functions can be incorporated into the package easily. We also demonstrate how to change prior information efficiently post-inversion, using the method of variational prior replacement. Contributions from the community are welcome, to make the package more broadly applicable.

SummaryElectrical resistivity tomography (ERT) is a widely used and effective tool for hydrogeological investigations. Conventional ERT inversion approaches are based on gradient-based algorithms, which typically provide deterministic optimal solutions, which are subject to uncertainty. Such uncertainty could have significant impact on hydrogeological interpretation using ERT. Model appraisal is a critical step after inversion, however, conventional appraisal methods are qualitative and thus subjective. To address these limitations, this study introduces a probabilistic variational inference (VI) method, referred to as Stein variational gradient descent (SVGD), to quantify both resistivity distributions and associated uncertainties in ERT inversions. Synthetic examples are conducted to investigate the effects of configurations and noise, and to compare the performance of SVGD with conventional inversion and model appraisal techniques. A field case study and its model validation are also presented to demonstrate the practical advantages of uncertainty quantification in field. The results indicate that SVGD can effectively reduce artifacts introduced by regularization and provide more comprehensive quantitative insights into subsurface structures compared to conventional approaches. The study also reveals limitations in the interpretation of basic statistics of uncertainty estimates, highlighting the need to examine the entire posterior distributions of parameter values. Additionally, this study demonstrates that the final uncertainty arises from a trade-off among multiple factors, such as geometry of subsurface structures, measurement techniques and data noise levels. Finally, we also discuss some comparisons with other probabilistic frameworks in hydrogeophysics, highlighting its potential to improve uncertainty and probability quantification in ERT, and possible future developments in hydrogeophysical coupled inversion.

SummaryUnderstanding the internal structure of the Earth is achieved using geophysical data and inversion is a powerful mathematical technique used by resource explorers to do so. Inherent ambiguity means that an infinite number of petrophysical models exist that can explain the geophysical data, so constraints such as geological models and petrophysical data have been employed to reduce the solution space. The constraints, like the data, are subject to noise and error, resulting in uncertainty propagating to the final model because inversion is designed to use the algorithm and constraints to find the single ‘best’ solution. Current practice assumes the best solution is found by optimising for the lowest misfit between the data and model; however, if the data is uncertain, the model fit to that data is likewise uncertain and potentially misrepresentative. Optimising misfit also means that inversion is subject to overfitting. Overfitting occurs when a model achieves the lowest misfit values by inadvertently fitting to data noise. Overfitting inversion occurs when the model has too many free parameters with no constraints, resulting in near-surface anomalies that can be mistakenly identified as legitimate targets for exploration rather than model artefacts. This contribution describes the use of spatial uncertainty calculated from geophysical data, providing free parameter constraints to reduce overfitting for geophysical inversion. The spatial uncertainty estimate is taken from a geostatistical model calculated using Integrated Nested Laplacian Approximation (INLA). A region in the East Kimberley, northern Western Australia, is subject to gravity inversion using Tomofast-x, an open-source inversion platform. Inversion is conducted using different configurations. Inversion is run without spatial uncertainty constraints, as is current practice, and then with spatial uncertainty constraints to test their effect on the resulting petrophysical model. The geostatistical model offers different percentiles from the geophysical model representing the extrema of estimated gravimetry values in the 10th and 90th percentiles. Inversions are run using these ‘extrema’ alongside the current practice of using the 50th percentile (or ‘mean’) gravity models as the observed field. Examination of inversion using and not using spatial uncertainty constraints shows that overfitting can be reduced. Using the extrema percentiles as the observed field has lesser benefits to reduce overfitting.

SummaryThe Earth’s ancient magnetic field is challenging to constrain from the rock record in large part due to the presence of non-ideal magnetic recorders in addition to processes, like alteration, that affect the ability of a material to reliably record field strength. Of the magnetic minerals present on Earth’s surface, magnetite is one of the most commonly used to simultaneously recover palaeomagnetic direction and intensity. Recent work on archaeological artifacts and clinker deposits (sedimentary rocks baked by coal seam fires) has identified a potential new mineral capable of recording the full-vector magnetic field: ɛ-Fe2O3, a high-T metastable phase of hematite. The palaeomagnetic potential of ɛ-Fe2O3, specifically regarding palaeointensity, has not been studied in depth. Further, recent work on synthetic ɛ-Fe2O3 has raised questions about the reliability of this phase for palaeointensity recording. To understand whether ɛ-Fe2O3 is a trustworthy full-vector magnetic recorder, more work is needed to assess this phase in its natural form. Here, we present results from Thellier-style palaeointensity experiments using a lab-induced thermoremanent magnetization (TRM) on natural ɛ-Fe2O3 present in Quaternary age clinker samples from the Custer National Forest, Montana, USA. The experimental setup was designed in attempt to isolate the ɛ-Fe2O3 phase from other magnetic carriers. The results of our study suggest that natural ɛ-Fe2O3 can reliably record palaeointensity and palaeodirections, yielding palaeointensity estimates within 5% and directions consistent with the applied laboratory TRM field. These new results suggest that ɛ-Fe2O3 bearing artifacts and clinkers can be robust full-vector magnetic recorders. Overall, this study adds confidence to previously obtained archaeomagnetic data and to a novel palaeomagnetic recorder, clinkers, opening the door to a more detailed characterization of the recent field.

SummaryContinental collision is prevalent along the Tethyan tectonic belt, characterized by diverse deformation patterns across regions, including concentrated deformation in the Alps, integral deformation throughout the Tibetan Plateau, and separate deformation within the Iranian Plateau. However, the mechanisms governing the diversity of deformation in different collisional orogens along the Tethyan tectonic belt remain poorly understood. Accretion of continental terranes during the closure of the Paleo- and Neo-Tethys oceans generated a highly heterogeneous lithosphere along the southern margin of Eurasia, a crucial factor in interpreting continental deformation. This study employs 2D thermo-mechanical numerical modeling to assess how tectonic inheritance-induced rheological heterogeneities govern deformation patterns in continental collision orogens. Our simulation results reveal three end-member deformation patterns resulting from variations in the rheology of the upper plate within the collision system. When the upper plate is uniformly strong, it prevents deformation from propagating into the interior of the continent, resulting in concentrated deformation in the collision front. If the upper plate is uniformly weak, deformation occurs throughout the entire upper plate, resulting in an integral deformation pattern. When a rheologically weak block is embedded in the strong upper plate, deformation concentrates in the collision zone and the weak block, resulting in separate deformation within the upper plate. Changes in the rheology of the bounding plates, the convergence rate, and the total convergence amount would not alter the basic deformation pattern of the continental collision system, if the rheology of the upper plate remain unchanged. Based on our simulation results, we suggest that the rheological characteristics of the upper plate govern the deformation patterns in continental collision systems. Our simulation results provide first-order explanations for the observed diversity of deformation in different continental collision systems along the Tethyan tectonic belt.

SummaryThe dispersion of Scholte waves provides a fundamental basis for inverting shallow seafloor elastic parameters. With the expansion of marine exploration, an isotropic seabed approximation has become increasingly inadequate. Therefore, in this study, Scholte-wave dispersion was analyzed in vertically transversely isotropic (VTI) media and the sensitivities of key parameters were quantified. Using a reduced delta-matrix formulation, a numerically stable dispersion equation for fluid-solid-coupled VTI media was derived and validated with elastic wavefield modelling and frequency-velocity spectra. Sensitivity tests on three representative seabed models [velocity increasing with depth (VID), a low-velocity layer (LVL), and a high-velocity layer (HVL)] show that anisotropy amplifies phase-velocity sensitivity to P-wave velocity (VP), especially for higher modes. In contrast, sensitivities to Thomsen parameters ε and δ are secondary but non-negligible. As mode order increases, the sensitive frequency band broadens and penetrates to greater depths. For the HVL model, dispersion is particularly sensitive to the overburden above the high-velocity layer. By contrast, for the LVL model, sensitivity concentrates within the low-velocity layer itself and above it. These sensitivity patterns reflect the influences of different parameters on inversion results and support the development of dispersion curve inversion for anisotropic shallow seafloor.

SummaryReflection waveform inversion (RWI) is an effective method for reconstructing subsurface parameters with low-to-moderate wavenumbers. As the influence of anisotropy on seismic data becomes increasingly significant, RWI should be extended to tilted transversely isotropic (TTI) media (TTI-RWI) to improve inversion accuracy. Unlike conventional isotropy or vertical transverse isotropy (VTI) assumptions, the TTI model provides a more realistic representation of geological structures with intense tectonic activity. Nevertheless, the practical implementation of TTI-RWI faces two challenges. First, as it relies on waveform matching, an inaccurate initial model can cause cycle-skipping and convergence to local minima. Second, the inherent coupling between velocity and anisotropic parameters leads to significant parameter crosstalk. These issues often coexist when prior information is limited. To address the first challenge, we propose a modified gradient sampling algorithm (GSA) that incorporates global optimization information to mitigate cycle-skipping without increasing computational cost. For the second challenge, we design a two-stage inversion strategy where the vertical P-wave velocity vp0 is first inverted using GSA, followed by joint inversion of vp0 and the anisotropic parameter ε via Gauss-Newton optimization. The effectiveness of the proposed TTI-RWI approach is validated through numerical experiments on the Overthrust model and applications to field marine towed-streamer data.

SummaryRobust, unbiased statistics describing long-term geomagnetic behaviour are sorely needed to elucidate the dynamics and evolution of Earth’s magnetic field and the geodynamo which produces it. While palaeomagnetic data are available across much of Earth’s history, their utility is hampered by highly inhomogeneous distributions in space and time and by associated uncertainties. To address this, a set of parameters based on robust statistics and describing the average strengths of the axial dipolar and non-axial dipolar components of the field, the time-variability of the total field, and certain ratios of these are proposed. A framework for estimating these parameters is developed whereby global datasets of palaeomagnetic directions and intensities are compared to outputs from an ensemble of numerical geodynamo simulations. A bespoke Monte-Carlo proxy-based approach allows measurement uncertainties and spatial inhomogeneity in the data to be accounted for and the framework further allows for independent validation tests to be performed. Estimates of these parameters obtained for three intervals: 0.1–1, 1–4, and 4–15 million years (Myr) ago, provide benchmarks against which field models and geodynamo simulations may be compared. Furthermore, the values obtained suggest that: (1) 0.9 Myr is an insufficient duration for fully defining the time-averaged field; (2) average axial and nonaxial dipole field strengths in the interval 0.1-1 Myr were ~50 per cent higher than in the two preceding intervals; (3) the time-variances of the total field in the three intervals were not distinguishable. In addition to demonstrating the utility of the new framework, these findings can potentially address a longstanding question in geomagnetism: why is a polarity reversal ‘overdue’?

SummaryNortheast China hosts one of the largest intraplate Cenozoic volcanic provinces and has experienced multiple collisions during the Paleozoic, extension during the Late Jurassic–Early Cretaceous and compression during the Pliocene. Tectonism in Northeast China has been largely controlled by subduction of the western Pacific plate since the Mesozoic and is typically characterized by the formation of multiple intraplate volcanic groups and sedimentary basins. The mechanism underlying the tectonism in this area, particularly the origin of the Cenozoic intraplate volcanoes and the evolution of the supersedimentary Songliao basin, remains controversial. To address these issues, we conducted seismic tomography to image the P-wave velocity and azimuthal anisotropy of the crust and uppermost mantle beneath Northeast China. In this study, we adopt an eikonal equation-based traveltime tomography method to invert high-quality P-wave first arrivals. We manually pick 21,006 P-wave first arrivals from 890 regional earthquakes recorded by 426 broadband seismic stations. Four prominent features are revealed by tomographic inversion. First, the results reveal a significant low-velocity anomaly in the uppermost mantle of the Changbaishan volcano and strong azimuthal anisotropy with E–W-oriented fast velocity directions distributed along the low-velocity anomaly. This feature indicates horizontal flow in the uppermost mantle beneath the Changbaishan volcano. Second, a prominent low-velocity anomaly is present in the mid-lower crust below the Changbaishan volcano, implying the presence of a magma chamber. Third, the crust of the Wudalianchi volcano is characterized by a nearly normal velocity structure and strong azimuthal anisotropy with N–S-oriented fast velocity directions, suggesting that magmatic activity has little effect on the crustal structure. Fourth, a widespread distinct low-velocity anomaly in the mid-lower crust beneath the Songliao basin reflects the mechanically weak properties of the mid-lower crust.

SummaryThe western South Tianshan foreland records late Cenozoic deformation associated with the India-Eurasia collision, yet the timing and nature of Miocene kinematic changes remain poorly constrained. Here we present new magnetostratigraphic, paleomagnetic, and anisotropy of magnetic susceptibility (AMS) data from a ~12–6 Ma succession in the western Keping fold-and-thrust belt (FTB). Paleomagnetic results from 39 site-mean directions reveal small-magnitude vertical-axis rotations since ~12 Ma, characterized by two distinct rotational phases: an earlier clockwise (CW) rotation (potentially reaching ~8-9° when evaluated relative to a younger counterclockwise (CCW) background) prior to ~10 Ma, followed by a persistent but minor CCW rotation (~4°) from ~10 to 6 Ma. Although the magnitude of rotation is limited, this pattern indicates a subtle change in rotational behavior. Importantly, the persistence of the CCW rotation throughout the younger interval suggests that the observed rotations were not fully acquired during deposition, but may have been modified by deformation younger than ~6 Ma. AMS fabrics show corresponding variations in magnetic anisotropy, indicating a shift from relatively organized tectonic strain to more distributed deformation. We interpret these results as reflecting progressive basinward propagation of thrusting in the South Tianshan foreland, with rotation-related deformation occurring during a relatively late stage. Overall, the dataset highlights the limited magnitude and young timing of rotational deformation within the Keping FTB.

SummaryThis study investigates the crustal and uppermost mantle architecture beneath the São Francisco Craton (SFC), which constitutes the core of the broader São Francisco Paleocontinent (SFP), and its surrounding tectonic provinces through Rayleigh wave tomography, integrating ambient-noise (periods of 6–50 s) and earthquake-derived (periods of 9–180 s) dispersion curves. Two-dimensional phase and group velocity maps were regionalized using adaptive parameterization, with the resolution assessed from checkerboard tests. A pseudo-3D shear-wave velocity (VS) model was generated down to 70 km depth, from which crustal thickness was also derived using the maximum velocity gradient method. Results at shallow depths (2–10 km) identify the Paraná, Parnaíba, and Tucano–Jatobá basins as low-velocity anomalies, while the São Franciscan Basin is not fully resolved because its reduced thickness falls below the model’s resolution limit, despite its broad surface extent. In the middle-to-lower crust (20–40 km) inside SFC, a low VS corridor characterizes the Paramirim Aulacogen, highlighting the role of inherited rift structures and subsequent thermal reworking within the cratonic interior. At greater depths (60–70 km), the Borborema Province exhibits low velocities that contrast with the high velocities of the stable SFC root. The Moho map derived from tomography indicates crustal thickening beneath the Paraná and Parnaíba basins and the Brasília Belt, in good agreement with receiver-function estimates. Overall, the VS anomalies and Moho geometry in the regions neighboring the SFC reveal high-velocity corridors with relatively thin crust (32-36 km) extending across the Tocantins, Mantiqueira, and Borborema provinces, and projecting northwestward beneath the Parnaíba Basin. These results demonstrate that the boundaries of the São Francisco Paleocontinent extend significantly beyond its exposed surface limits within the crust and uppermost mantle. These boundaries are clearly discernible mainly at lower crustal depths and likely reach the upper crust. Furthermore, marginal deformations are primarily restricted to shallower levels of the crust, suggesting the preservation of a mechanically strong and continuous cratonic foundation beneath the surrounding orogenic belts and intracratonic basins. The main exception occurs along the southwestern margin, where the absence of a clear seismic boundary between the SFP and the Paranapanema Block suggests deep lithospheric integration or a boundary too narrow to be resolved by the present station geometry.

SummaryAutomated seismic event classification is a critical component of modern earthquake monitoring and network operations, yet many previous studies have been limited by small datasets or binary tasks. This work presents the first systematic benchmark of mainstream deep learning models, including convolutional neural networks (CNNs), Transformer-based architectures, and Capsule Networks (CapsNet), on the large-scale DiTing 2.0 AI seismic dataset, which contains 19,384 labeled three-component waveforms spanning three classes (natural earthquakes, quarry blasts, and mine collapses). Thus, we provide reproducible baselines for the seismic events classifications. Several CapsNet variants optimized for DiTing 2.0 are evaluated, and our results show that the CapsNet+Res model using MFCC representations and data augmentation achieves 91.08% accuracy (weighted F1 = 91.10%) on the held-out test set. The multi-station voting further improves event-level accuracy to 97.52%, while a companion noise-event classifier attains 98.47% accuracy. Functionality testing on demonstration continuous records confirms reliable end-to-end operation within a transferable and user-friendly system, underscoring its feasibility for seismic network applications. Overall, this study bridges methodological development and operational application by providing robust baselines, insights into the interplay of input features and architectures, and a practical platform for automated classification; large-scale continuous-data evaluation, cross-regional transfer validation, and adaptive learning strategies remain important directions for future research.

SummarySatellite altimetry technology can recover the marine gravity field by measuring Sea Surface Heights (SSHs) with high precision. However, traditional methods, relying on linearized SSH–gravity relations, fail to capture complex nonlinear characteristics. Meanwhile, the accuracy of the altimeter-only gravity field is often compromised in shallow depth areas due to poor-quality altimetric signals. To address these issues, this study proposes a method for recovering gravity anomalies that combines Back Propagation Neural Network (BPNN) with multi-source data. The BPNN establishes a nonlinear relationship between gravity and input parameters, including Deflections of the Vertical (DOVs), Seafloor Topography (ST), Vertical Gravity Gradients (VGGs), and Gravity Anomalies (GAs), thereby constructing a gravity anomaly model for the South China Sea. For benchmarking, gravity is also derived with the classical Inverse Vening–Meinesz (IVM) method and validated against independent shipborne gravity which is applied to evaluate the performance of the gravity model. The results demonstrate that the BPNN method outperforms the IVM method, achieving an accuracy improvement of 1.08 mGal overall, and 1.61 mGal in shallow depth areas. Additionally, compared with the reference gravity models (SWOT and DTU17), the gravity model derived by the BPNN method achieves an accuracy improvement of 0.04 mGal and 0.85 mGal, respectively. Power spectra analysis further reveals that the improvements from the BPNN method are most significant in the wavelength range of 5-100 km. The improved accuracy is attributed to the effective incorporation of ST, VGG and prior GA information. The results show that the BPNN method effectively captures nonlinear features and has significant potential for marine gravity field recovery.

SummaryGlaciers are key components of the global climate system and sensitive indicators of environmental change. Their dynamics generate diverse seismic signals, whose source mechanisms offer valuable insights into their internal stress conditions. While moment tensor inversion has been applied to icequakes on a few alpine and polar glaciers, it had not yet been implemented on the Argentière Glacier (French Alps). In this study, we conduct a systematic characterization of icequake source mechanisms based on a dense dataset of 14 057 near-surface events recorded by 98 3-component sensors deployed at the surface of the glacier during the RESOLVE project. We apply a full waveform inversion method to jointly reconstruct the moment tensor and the source time wavelet for each event. The moment tensor Green’s functions used in the inversion are computed through numerical modeling of elastic wave propagation in a 3D medium, incorporating real surface topography. This approach allows us to exploit the full complexity of the recorded seismic signals and to move beyond previous analysis based on simplified models and single-component data. The results reveal a clear dominance of opening-type (tensile crack) mechanisms, consistent with extensional stress regimes at the crevasse locations, with principal stress direction almost perpendicular to the local crevasse orientations. The exceptional size of the catalog enables a detailed investigation of spatial patterns in source mechanisms, particularly highlighting structural complexity in the heavily crevassed downstream zone. The distribution of extensional and compressional mechanisms further indicates a highly heterogeneous stress field at the glacier surface, influenced by local crevasse geometry. Depth-dependent variations in the reconstructed moment tensors suggest that deeper events tend to involve more isotropic components, likely reflecting pressure-driven failure under overburden stress. These findings demonstrate the potential of full waveform inversion to characterize the source mechanisms associated with the icequakes on a glacier. This work represents a significant step toward integrating seismological modeling with glaciological interpretation in alpine environments.

SummaryKinematic characteristics (creeping or locked) and high-precision seismic catalogs can constrain the shallow (<20 km) slip pattern of active fault zone. We collect Sentinel-1 Synthetic Aperture Radar (SAR) images and extract a high-resolution deformation velocity field along the active Laohushan-Haiyuan (LHS-HY) fault zone in the northeastern margin of the Qinghai-Tibet Plateau. We invert the shallow fault coupling and slip distribution using two-dimensional (2D) and three-dimensional (3D) models, indicating that the fault zone exhibits an alternating pattern of large strong coupling asperities and creeping zones, and the deep slip rate decreases from 5.2 mm/yr in the west to 3.4 mm/yr in the east, accompanied by a transition from strike-slip to dip-slip components. Then we calculate cumulative seismic energy release, seismic slip rate, and statistical parameters including $b - \textit{value}$, coefficient of variation of seismicity interevent times, and Nearest-Neighbor Distance (NND) with regional seismic catalog. The geodetic and seismic results demonstrate a complex shallow slip pattern in the fault zone. The following characteristics are highlighted. A significant throughgoing locked-creeping transition zone with variable depth range extends from the eastern part of the Laohushan segment (LHS) to the eastern segment of Haiyuan Fault (HYE). A shallow (<6 km) creeping zone with weak coupling and seismicity in the western HYE segment differs from the shallow part of the locked-creeping transition zone between the eastern LHS segment and the western part of the western segment of Haiyuan Fault (HYW). A transition zone with strong coupling and active seismicity in the eastern HYE segment ranges from 4 km to 12 km in depth. The results provide new insights into the shallow slip behavior of the LHS-HY fault zone, and offer valuable references for seismic hazard assessment in the region.

SummaryAccurate sensor orientation estimation is critical for reliable seismological processing, especially when rotating three-component seismograms is required. In this study, we determine the sensor orientation angles of 676 broadband stations of ChinArray-II deployed in northeastern Tibet between August 2013 and June 2016. The polarizations of both Rayleigh waves and teleseismic P-waves are used to estimate the azimuthal deviation. The results demonstrate that both approaches are consistent and approximately 600 stations are well-aligned, with mis-orientation angles less than 10°. The remaining stations exhibit various orientation problems, such as vertical component reversal and temporal variations in sensor alignments. Moreover, detailed multi-event analysis reveals that three-component sensor gain discrepancies may lead to failures of both P- and Rayleigh-wave approaches, while post-validation of multi-event estimation can identify such issues. Compared with previous studies, our results provide comprehensive sensor orientation information and indicate that combining noise level and wave polarization yields robust estimations.

SummaryThe South Peru subduction zone is a complex, highly active region, which has hosted four Mw 8 + earthquakes over the last 100 years. It marks the transition between the flat slab associated with the Nazca Ridge subduction in the North and more steeply dipping subduction in the South, causing the slab to contort and affecting seismicity patterns in the region. In this study, we present the first high-density, high-quality seismic catalog of the region between the arc and the trench, totaling 166 825 events between January 1st 2022 and December 31st 2024, including 125 467 well-located ones. We first picked and associated phases using PhaseNet and PyOcto, then located the resulting events with NonLinLoc-SSST and GrowClust3D. Finally, we derived a new slab model from the seismicity, allowing us to classify the earthquakes as upper plate (16 per cent), interface (12 per cent), lower plate (68 per cent), outer rise (0.20 per cent) and human-related (3.1 per cent).The region is broadly divided into four subregions with different seismicity patterns and slab geometries: the flat slab, with intense interface and intraslab activity, the slab transition zone, where the plate contorts to accommodate its change in geometry, the Arequipa region, with intense upper plate seismicity but very low intraslab and interface seismicity, and the North Chile region, with a large band of dense intraslab seismicity.We find that in the flat slab region, the Nazca Ridge is linked to the presence of dense seismicity close to the trench, and seismic swarms hinting at the presence of slow slip. Meanwhile, the intraslab seismicity in that region is organized in trench-parallel bands which are likely related to slab bending. In the slab transition region, we image multiple orthogonal faults just south of the slab contortion, suggesting a damaged slab. Further south, in the Arequipa region, upper plate seismicity forms a large, trenchward-dipping structure seemingly connected to the Incapuquio fault at the surface. Finally, in North Chile, the deep band of intraslab seismicity appears to locate further downdip as we move to the north, perhaps reflecting changes in slab properties.