Geophysical Journal International

SummaryHuang et al. (2025) reported the detection of 67 teleseismic marsquakes identified by P and S wave arrivals. The authors used a deep learning phase picker trained on local earthquake data and applied it to narrow-bandpass filtered seismic data recorded by NASA’s InSight seismometer, making use of similarities between local earthquake and teleiseismic marsquake recordings when adjusting for sampling rate and S-P time scaling relations. We review all detections as similarly done for the Marsquake Service catalogue and other studies on this data set, using the complementary wind and pressure data recorded by InSight. As these auxiliary data were not recorded in the second half of the mission, we also infer wind contamination from bandwidths in the seismic data that contain wind-sensitive lander modes. Additionally, we analyse the signal polarisation to compare it with the expected characteristics of P and S waves and the background noise. Our review indicates that all 67 detections reported by the authors correspond to atmospheric noise. In most cases, the detections relate to the seismic signature of small wind bursts followed by larger wind bursts, onsets of which are interpreted as P and S waves by the authors. Further, we show that if these events were interpreted as genuine marsquakes, their inferred epicentral distance distribution would not match typical marsquake distances, while their magnitudes would make them the largest events of the catalogue. For future studies that deal with seismic event detection and interpretation from InSight, we recommend a careful consideration of the established event and noise signal markers described in this comment and in the literature to avoid misinterpretation of noise as event signals.

SummaryHigh-speed train (HST) signals offer an abundant and eco-friendly seismic source along the railway, but their application to full waveform inversion (FWI) presents unique challenges due to complex source characteristics and field constraints. We develop an HST-based elastic FWI framework that models the train as a distributed pier-force: a chain of time-delayed excitations applied continuously along deeply embedded bridge piers. This source mechanism generates predominantly S- and Rayleigh-wave energy, providing enhanced shallow subsurface illumination. The synthetic anomaly experiment demonstrates that the distributed pier-force enables superior multi-parameter reconstruction, particularly achieving higher density accuracy than the explosive and single-force sources. Additional sparse acquisition tests validate the robustness of the method under limited receiver coverage. The field data application successfully reconstructs subsurface layering through simultaneous source and parameter inversion, supporting the physical plausibility of the distributed source model. Overall, this study establishes the distributed pier-force as an effective and computationally efficient HST source for shallow subsurface characterisation, while also highlighting limitations under realistic field conditions.

SummaryThe Laji Shan-Jishi Shan Tectonic Belt (L-JTB), situated at a crucial tectonic transfer position on the northeastern margin of the Tibetan Plateau, is important for understanding regional deformation partitioning and seismic hazard. Although it has traditionally been regarded as a zone of relatively modest deformation, the 2023 Jishishan Mw 6.0 earthquake highlights the need to reassess its present-day kinematics and mechanical role. In this study, we integrate GNSS and Sentinel-1 InSAR data to derive a high-resolution three-dimensional interseismic crustal deformation field. We then apply an enhanced dip-aware velocity-profile model within a Bayesian framework to estimate the slip rates and locking characteristics of the major faults, and we further calculate the regional strain-rate field using a multiscale spherical wavelet approach. The results indicate that: (1) The L-JTB exhibits a modest average regional strain level relative to the first-order boundary faults to its north and south, but also displays pronounced along-strike heterogeneity and localized deformation focusing within the belt; (2) The Laji Shan Fault is characterized by a comparatively weak interseismic signal and is dominated by shortening and uplift, with only a minor fault-parallel component, whereas the Jishi Shan Fault is more strongly active, accommodating dextral strike-slip at 1.7 ± 0.3 mm/yr together with shortening-related dip-slip at 3.5 ± 1.2 mm/yr; and (3) the L-JTB is better interpreted as an internal strain transfer belt between the dextral Riyue Shan Fault and the sinistral West Qinling Fault, in which part of the transferred deformation is converted into crustal shortening, uplift, and localized internal strain. Our study reveals that even within a tectonic transfer belt characterized by only modest average regional strain, moderate earthquakes may still nucleate where deformation becomes localized through favorable stepover geometry, structural segmentation, and local strain focusing.

SummaryWe investigate the 410 km discontinuity (thereafter the ‘410’) beneath Europe using teleseismic S-to-P converted waves. This discontinuity—associated with the olivine–wadsleyite phase transition at the top of the mantle transition zone (MTZ)—is widely used as an indicator of thermal variations linked to mantle upwellings and subducting slabs. Our results reveal complex structures of the ‘410’, including closely spaced discontinuities above and below 410 km depth, within laterally confined regions (∼100-200 km wide). These features are predominantly aligned along a corridor extending from the western Alpine front (Western Alps, Rhone Graben) through the Eifel volcanic fields and the Eger Graben to the eastern Alpine front (Western Carpathians, northern Pannonian Basin, Eastern Carpathians), along the European Cenozoic Rift System (ECRIS). In several locations, the disturbed ‘410’ is associated with an elevated lithosphere–asthenosphere boundary (LAB), suggesting a link between lithospheric processes and MTZ structure. We interpret these observations as evidence for small-scale lithospheric dripping, potentially initiated during or following the Alpine orogenesis. Additional occurrences of apparent ‘410‘ doubling are identified beneath the southern Scandes and the northern Adriatic region; beneath the Scandes, this feature spatially correlates with extensional tectonics. Overall, our results indicate that the ‘410’ beneath Europe is strongly influenced by smaller-scale mantle dynamics, closely related to the ECRIS, rather than reflecting solely large-scale thermal anomalies.

SummaryRayleigh wave dispersion curves inversion is an important method for shallow shear wave velocity structure imaging, which can be achieved through different frameworks such as deterministic inversion and Bayesian inversion. The deterministic methods with fixed parametrization usually require pre-set model complexity, and are difficult to directly provide posterior uncertainty estimation. In contrast, trans-dimensional Bayesian method can probabilistically estimate the dimensions of the model during the sampling process and quantify the uncertainty of the inversion results. However, in the inversion of multimode Rayleigh wave dispersion curves, the posterior space usually has high-dimensional, multi-modal, and strongly nonlinear characteristics. How to achieve efficient posterior exploration and stable trans-dimensional mixing is still a key issue in practical applications. In response to this issue, we constructed and evaluated a trans-dimensional Parallel Tempering reversible jump Markov Chain Monte Carlo (PT-rjMCMC) inversion workflow for multi-modal Rayleigh wave dispersion curves in shear wave velocity imaging, denoted as All-Pair-Sweep PT-rjMCMC (APS-PT-rjMCMC). The method integrated Voronoi trans-dimensional parameterization, multi-modal dispersion likelihood function, reversible jump model update, and parallel tempering sampling into a unified framework. In the replica exchange stage, it adopted an all-pair-sweep replica-exchange schedule with randomized ordering to enhance the inter chain information propagation and trans-dimensional mixing ability under a limited number of temperature chains. The inversion results of synthesized model and measured data indicated that compared with the benchmark implementation, the workflow exhibited better performance in convergence behavior, posterior structure recovery, and layer identification. Our technology provides a solution that combines adaptability and reliability for fine survey of shallow geological structures. It is effectively improving the inversion accuracy of shear wave velocity structures under complex geological conditions. It has broad application space and significant application value in fields such as engineering survey, geological hazard assessment, and water resources investigations.

AbstractThe Poisson equation governing a planet’s gravitational field is posed on the unbounded domain, $\mathbb {R}^3$, whereas finite-element computations require bounded meshes. We implement and compare three strategies for handling the infinite exterior in the finite-element method: (i) naive domain truncation; (ii) Dirichlet-to-Neumann (DtN) map on a truncated boundary; (iii) multipole expansion on a truncated boundary. While all these methods are known within the geophysical literature, we discuss their parallel implementations within modern open-source finite-element codes, focusing specifically on the widely-used MFEM package. We consider both calculating the gravitational potential for a static density structure and computing the linearised perturbation to the potential caused by a displacement field—a necessary step for coupling self-gravitation into planetary dynamics. In contrast to some earlier studies, we find that the domain truncation method can provide accurate solutions at an acceptable cost, with suitable coarsening of the mesh within the exterior domain. Nevertheless, the DtN and multipole methods provide superior accuracy at a lower cost within large-scale parallel geophysical simulations despite their need for non-local communication associated with spherical harmonic expansions. The DtN method, in particular, admits an efficient parallel implementation based on an MPI-communicator limited to processors that contain part of the mesh’s outer boundary. A series of further illustrative calculations are provided to show the potential of the DtN and multipole methods within realistic geophysical modelling.

SUMMARYNatural faults commonly contain fluid-saturated gouge layers, in which fluid injection can modify pore pressure and porosity evolution, thereby affecting slip stability and induced seismicity. Here we develop a spring-slider model based on rate-and-state friction (RSF) to investigate fault slip evolution under dry, fluid-saturated, and fluid injection conditions. Our model incorporates gouge dilatancy/compaction and fluid-related pore pressure effects. Our results show pronounced differences in the onset time of the first dynamic instability and the peak slip rate among these cases. Compared to the dry case, fluid saturation without injection delays instability and slightly lowers the peak slip rate, whereas rapid injection-induced pressurization triggers earlier dynamic slip and higher peak slip rates. Without injection, increasing the dilatancy coefficient systematically delays instability. Under rapid injection, however, the onset time becomes much less sensitive to dilatancy, indicating a gradual transition from a dilatancy-influenced to an injection-dominated nucleation regime as the injection-dilatancy competition number increases. Linear stability analysis further suggests that fault stability can be characterized by a generalized critical stiffness that combines the effects of effective normal stress, pressurization rate, and dilatancy/compaction feedback. These results indicate that fluid effects on fault rupture arise from the competition between stabilizing dilatancy hardening and destabilizing time-dependent pressurization, highlighting that injection-induced seismicity can be understood as an injection-rate-driven stability problem. Our findings provide a physical framework for understanding the transition from dilatancy-sensitive to injection-controlled fault slip within the explored net dilatant regime under different fluid environments.

SummaryThis study leverages a new, improved and densified GNSS velocity field of the western Aegean region to quantify slip rates, strain localisation, and interseismic loading within the upper plate of the Hellenic subduction zone, including the deformation systems associated with the subduction–collision transition around Cephalonia, the Hellenic forearc extension, and the southwestern termination of the North Anatolian Fault system. We examine several active tectonic domains, comprising four extensional regions (Corinth–Patras Rift, Evia Gulf, Argolic Gulf, southwestern Peloponnese) and three strike-slip systems (Cephalonia Transform Fault, Katouna–Stamna Fault System, Movri Fault Zone). Across the Corinth Rift, NS extension increases westward from ≈ 7 to ≈ 15 mm.yr$^{\hspace{1.0pt}\text{--}1}$, of which up to ≈ 6 mm.yr$^{\hspace{1.0pt}\text{--}1}$ is accommodated offshore. Velocity profiles indicate combined elastic loading and aseismic creep on a limited number of crustal-scale faults. The Evia–Boeotia sector undergoes NS extension at up to 8 mm.yr$^{\hspace{1.0pt}\text{--}1}$, but deformation is distributed across multiple structures, each accommodating creep or elastic loading at rates <2 mm.yr$^{\hspace{1.0pt}\text{--}1}$. In the southern Peloponnese, diffuse EW extension of up to 6 mm.yr$^{\hspace{1.0pt}\text{--}1}$ occurs alongside 1–2 mm.yr$^{\hspace{1.0pt}\text{--}1}$ of NS extension in the central Peloponnese. A portion of this EW deformation may be accumulating interseismically as elastic strain on prominent structures, such as the Sparti and East Messenia faults. No measurable strain is detected across the Argolic Gulf, suggesting substantially lower present-day loading rates on the Astros Fault than previously inferred. Strike-slip systems display contrasting behaviours. The Katouna segment accommodates transtensional left-lateral creep of ≈ 13 mm.yr$^{\hspace{1.0pt}\text{--}1}$ within a zone <6 km wide, whereas slip decreases to ≈ 8 mm.yr$^{\hspace{1.0pt}\text{--}1}$ on the Stamna segment, consistent with strain transfer through the Trichonida pull-apart basin and the Nafpaktia diffuse shear zone. In contrast, the Movri Fault appears locked down to at least 10 km depth, accumulating ≈ 4 mm.yr$^{\hspace{1.0pt}\text{--}1}$ of right-lateral strain. Onshore velocities near the Cephalonia Transform Fault indicate an onshore half-rate of elastic loading of ≈ 8 mm.yr$^{\hspace{1.0pt}\text{--}1}$, suggesting that the full transpressional right-lateral motion (≈ 16 mm.yr$^{\hspace{1.0pt}\text{--}1}$) accumulates interseismically, highlighting considerable seismic hazard potential.

SummaryDistributed Acoustic Sensing (DAS) data often contain various types of noise, including random noise, coherent noise (e.g., coupling or linear noise), and common mode noise, which significantly degrade seismic signal quality. Conventional denoising methods struggle to effectively suppress diverse noise components while preserving important seismic signals. To address this issue, we propose a denoising self-supervised cascade network (DAS-DSCnet), a multi-stage neural network designed to progressively denoise DAS data without requiring external labels or synthetic training data generation. The network consists of three stages: Stage 1 targets random noise using a Noise2Noise-based approach; Stage 2 suppresses dataset-specific coherent noise using a denoising convolutional neural network (DnCNN)-based network trained with internally extracted noise patches; and Stage 3 predicts and removes common mode noise through trace shuffling and a Noise2Noise-based model. Training data for each stage are generated directly from the input DAS data by exploiting the data’s inherent characteristics, enabling efficient learning that reflects field-specific noise features. The model was evaluated using two distinct field DAS datasets with different noise patterns. The results demonstrate that DAS-DSCnet achieves superior noise suppression compared to conventional approaches, enhancing signal continuity while minimizing leakage. The denoising performance remains stable across different stacking configurations and hyperparameters, confirming the model’s robustness. Therefore, DAS-DSCnet offers a scalable and practical framework for improving seismic data quality in DAS applications, demonstrating the potential for fully automated, data-driven denoising in large-scale seismic monitoring.

SUMMARYWe present a comprehensive dataset of 920 coordinates and 509 velocities for geodetic points in central Greece and the Peloponnese, an area characterised by intense tectonic deformation. The points, with observation periods within the 1990–2024 range, are organised into three categories: permanent stations, triangulation pillars, and markers. The latter two categories are subdivided according to whether or not they feature self-centring. Most of the triangulation pillars belong to the Greek national network originally surveyed in the 1960s–70s. The GNSS data were processed using the GIPSY 6.4 software. To assess the secular velocities, we corrected for co-seismic and post-seismic displacements using earthquake parameters constrained by the time series of the permanent stations. Self-centring systems improve precision, reducing the average horizontal coordinate residual variability from 6.15 to 4.45 mm. The velocity uncertainties stabilise below 0.15 mm yr−1 when the time series exceed twenty years. Points with self-centring achieve 0.2 mm yr−1 accuracy after twelve years of data, compared to twenty years for those without self-centring. After twenty-five years, campaign points observed eight to ten times match the precision of permanent stations. The velocities at the campaign points further validate the HELVEL model previously developed using permanent stations only. We calculate a seven-parameter transformation from the original coordinates of 424 triangulation pillars to their GNSS-based ITRF2020 coordinates at epoch 2020.0. The lowest mean scatter after the transformation is 0.134 m when 1965 is used as the mean epoch for the triangulation data. We then apply this transformation to all 9,729 pillars of the study area. At the 424 resurveyed pillars, the GNSS ellipsoidal heights agree with the sum of the levelled heights and the official HG2023 geoid heights to within 0.184 m root-mean-square. Our dataset is entirely referenced to ITRF2020 at epoch 2020.0, which enables interoperability with previous and future geodetic studies. Dense campaign point arrays are critical for resolving the strain distribution at the scale of individual active faults, beyond the reach of arrays of permanent stations alone.

AbstractMantle viscosity remains one of the largest outstanding uncertainties in global geodynamics. Time-dependent mantle circulation models that assimilate tectonic histories (MCMs) provide a way to test viscosity by assessing their present-day predictions against observations. This approach allows for the influence of viscosity on mantle density structure to be accounted for, which is not possible using instantaneous modelling approaches. Here we present the first systematic test of lower mantle viscosity against dynamic topography, the geoid, and seismic heterogeneity using high-resolution MCMs. Model density structure depends strongly on the assumed viscosity profile, which in turn controls the fit to seismic heterogeneity. The fit to dynamic topography and the geoid is further influenced by the instantaneous transmission of stresses to the surface. These two effects can either reinforce or counteract each other at different depths, which must be considered when attempting to match dynamic topography and geoid amplitudes. MCMs typically overestimate dynamic topography amplitudes. We find that it is possible to reduce these amplitudes by lowering viscosity in the upper lower mantle (≈660-2000 km), though this comes at the expense of a reduced fit to the geoid and/or seismic heterogeneity. Our preferred viscosity profile provides an excellent fit to observed geoid amplitudes and the seismic heterogeneity of S40RTS. We also tested an alternate tectonic reconstruction with tomography-based refinements around the Pacific which improved the correlation with the observed geoid by ≈20%. Our results show that MCMs can now reach a level of resolution and realism sufficient for comparison to multiple independent data sets, opening the door to systematic assessment of uncertain parameters which govern convection in the mantle.

SUMMARYThe excitation and propagation of multiple wave types, including seismic waves, ocean acoustic waves, and tsunamis triggered by earthquakes within the oceanic wavefield, constitute a problem of substantial scientific and practical challenge. This phenomenon involves complex interactions of waves within a fluid-solid coupled system, which is critical for both fundamental geophysical understanding and enhancing hazard assessment. While several numerical methods have been developed to simulate the full wavefield, few studies have systematically explored the crucial influence of complex seafloor topography on coupled wave dynamics. This study introduces a novel earthquake-tsunami coupling simulation method within a 2-D spectral-element method (SEM) framework, leveraging its flexibility to handle complex geometries and accuracy for long-range wave propagation. To validate the accuracy of the simulated seismic waves, ocean acoustic waves, and tsunamis, we quantitatively evaluate the permanent seafloor displacement, yielding a high correlation coefficient of 0.997 and a negligible error of 5 × 10−3 compared with the analytical solution. The mean relative error of the calculated tsunami phase velocities of the proposed method with those from the propagator matrix method is only 0.12%. Furthermore, we establish two distinct numerical models—one incorporating irregular bathymetry and another with an idealized flat bathymetry—to systematically investigate the effects of bathymetry on the oceanic wavefield. Our results demonstrate that the irregular bathymetry significantly influences the propagation characteristics of both seismic waves and tsunamis, altering wave amplitudes, travel times, and spatial patterns. We further decompose the contributions of seawater and seafloor geometry, highlighting their respective roles in shaping the overall wavefield. Additionally, we examine the influence of varying earthquake source locations on wave propagation paths, emphasizing the importance of accurately modelling bathymetry for offshore seismic events. Overall, our proposed 2-D earthquake-tsunami coupling simulation framework provides a powerful tool for comprehensively understanding the oceanic wavefield under gravity and offers significant potential for improved earthquake and tsunami hazard assessment, particularly when combined with seismological and oceanographic observations.

AbstractSeismicity rates in west Texas and southeast New Mexico have increased over the last nine years and are in large part driven by subsurface wastewater disposal associated with oil-gas operations. Injection-induced seismicity is often explained as the result of fault weakening from fluid pressurization. However, fluid injection also induces poroelastic stresses from fluid-rock coupling, which in some cases are larger than the perturbations induced from pore pressure alone. In this work, we model in-zone changes in pore pressure and poroelastic stressing along four major fault zones that have hosted moderate-large ML 4 – 5 earthquakes in the Delaware Basin (DB) of west Texas. We leverage high-quality downhole pore-pressure measurements to constrain the in-situ hydraulic diffusivity and storativity. The data show that the deep injection interval has a storativity of ∼ 5×10−5 and a diffusivity between 23-65 m2/s, suggesting that this interval can pressurize rapidly and transmit fluid pressure efficiently. We view these as local hydraulic properties and use an ensemble modeling approach that accounts for a large range in diffusivities and storativities to model changes in Coulomb Failure Stresses (CFS). Our 2D fully coupled poroelastic models show that deep subsurface fluid injection can induce between ∼1-1000 kPa in CFS along basement rooted faults that penetrate the injection interval, with the largest values occurring in models that use the hydraulic properties inferred from our in-situ measurements. However, the induced changes in CFS are much smaller (∼ 20-30 kPa) when averaging over a large range in hydraulic properties. Irrespective of the model parameterization, the in-zone perturbations in CFS are dominated by changes in pore pressure, even at distances as far as 20-30 km from the nearest injection source. Our results highlight the importance of obtaining in-situ poromechanical measurements and indicate that such high-resolution measurements are critical to understanding subsurface stressing associated with fluid injection.

AbstractThe northern Adriatic Sea provides an exceptional setting for investigating tidal processes because of its shallow bathymetry, elongated basin geometry, and semi-enclosed configuration. These characteristics produce some of the largest tidal amplitudes in the Mediterranean and favor the amplification of both diurnal and semidiurnal constituents, leading to complex sea-level variability and episodic extreme events such as high stands along the coastal cities. We analyze tidal dynamics and ocean tidal loading (OTL) in the northern Adriatic using a multi-technique approach that combines tide gauge (TG) observations, interferometric reflectometry (GNSS-IR) sea-level retrievals, and GNSS precise point positioning (PPP) solutions describing crustal deformation. Tide gauge records confirm the progressive increase of semidiurnal tidal energy toward the northern end of the basin, with the M2 and S2 constituents dominating over the diurnal band. These observations broadly agree with the FES2014b ocean tide model, although local amplitude and phase deviations are observed in shallow and geometrically complex coastal environments. Sea-level time series derived from GNSS-IR at several coastal sites show a high degree of agreement with nearby tide gauges, with correlations exceeding 90%. Both diurnal and semidiurnal constituents are well resolved, and amplitude differences remain within 4-5 cm, demonstrating the potential of GNSS-IR as an effective and low-cost complement to traditional TG networks. GNSS PPP solutions further allow the estimation of three-dimensional OTL displacements at hourly temporal resolution. The vertical component is primarily controlled by the semidiurnal M2 tide and closely matches model predictions in both amplitude and phase. Larger discrepancies are observed for diurnal constituents, particularly K1, likely related to interactions with GNSS orbital periods and remaining systematic effects in the processing. Overall, this work presents the first high-temporal-resolution GNSS-based assessment of ocean tidal loading in the northern Adriatic. The strong consistency among GNSS, GNSS-IR, and TG observations highlights the capability of integrated GNSS approaches to simultaneously capture oceanographic variability and solid Earth tidal deformation, opening new perspectives for coastal sea-level monitoring, geodetic stability studies, and hazard assessment in a changing climate.

SummaryThe horizontal magnetic inter-station transfer function (M) offers distinct advantages in magnetotelluric (MT) studies due to its reduced susceptibility to shallow galvanic distortions. While its utility in constraining subsurface conductivity through 2D inversions is established, its resolution characteristics in three-dimensional (3D) scenarios—particularly regarding depth sensitivity and lateral recovery—remain poorly quantified. Here, we conduct a systematic investigation of M through 3D forward modelling, sensitivity analysis, and inversion of synthetic models, followed by a validation using long-period MT array data from the Eastern Pamir. Key findings reveal: (1) M exhibits response patterns analogous to the impedance tensor (Z), with an inverse component correspondence where diagonal elements of Z align with off-diagonal elements of M; (2) Reference station placement critically controls the inversion performance of M—locations above conductive anomalies distort anomalous currents and degrade data fit, whereas resistive homogeneous backgrounds enhance lateral resolution; (3) M resolves shallow anomalies with lateral boundary definition and resistivity contrast recovery superior to those of Z and the tipper (T) in sparse arrays; (4) Sensitivity tests indicate that M provides limited resolution for deep structures beyond the effective inductive scale, where its recovery capability diminishes significantly compared to Z; (5) Application to field data demonstrates that incorporating M improves the resolution of complex shallow structures and enhances the fit of Z data, with the joint inversion of Z + M + T yielding the most robust electrical model. We recommend using multiple reference stations for field data inversion to mitigate the impact of variations in reference site locations. This work establishes a quantitative framework for deploying M in field surveys and 3D inversions.

SummaryOceanic transform faults (TFs) are fundamental elements of plate tectonics and have traditionally been viewed as conservative strike-slip boundaries. Seafloor observations and numerical modelling suggest the existence of extensional stress, however how it manifest at depth remains unknown. Moreover, slow-slipping TFs are often associated with thin crust and possible exposures of serpentinised peridotite near the seafloor. Here we apply full waveform inversion (FWI) to a 12-km offset seismic dataset across the Romanche TF, the largest TF on the Earth. We use source-receiver reciprocity and downward continuation to emulate a split-spread ocean bottom cable survey geometry from one-sided surface streamer data, bringing the refracted waves ahead of reflections while accounting for rough seafloor topography. We then perform travel time tomography followed by FWI to the downward-continued data to derive a high-resolution crustal model. The resolution is about 0.7 km horizontally and 0.4 km vertically, down to 3.5–4 km depth from the seafloor. Our results reveal low P-wave velocity in the upper 3 km, suggestive of basaltic origin, and no evidence for high velocities characteristic of serpentinised peridotite on the valley floor. Moreover, we image inward dipping normal faults extending to ∼4 km depth, forming a flower-like structure. Regional earthquake data reveal strike-slip mechanisms along the transform and normal-faulting near the RTI, with strike-slip hypocenters aligning with interpreted faults. These features suggest that the Romanche TF resembles a trans-tensional regime with a deep-rooted strike-slip fault in the middle, accommodating local strain deformation.

SummaryAdvances in satellite gravimetry technologies have enabled the integration of increasingly diverse mission datasets for high-resolution static gravity field modeling. However, during the construction of regularization matrices for stabilizing Spherical Harmonic Coefficients (SHCs), conventional regularization methods generally neglect significant correlations among SHCs, primarily due to heterogeneous noise characteristics of observations from different missions. To address this limitation, we propose a Full Signal Variance-Covariance (FSVC) regularization method by constructing a full regularization matrix based on a priori gravity anomaly signal amplitudes. Applying this method to combined normal equations integrating GOCE SGG, GRACE, and Swarm observations yield three solutions under different constraint strategies: a Kaula diagonal constrained solution (Tongji-GMMG2025S-KLA), a Diagonal Signal Variance-Covariance (DSVC) regularized solution (Tongji-GMMG2025S-DSVC) derived from the diagonal elements of the FSVC matrix, and the FSVC-regularized solution (Tongji-GMMG2025S-FSVC). Our analyses demonstrate that: Based on FSVC analysis, the proposed FSVC regularization method exhibits overall superior performance compared to the diagonal regularization approach, particularly when the prior model incorporates terrestrial gravity data. Even when using the Kaula-constraint solution as the prior model, quantitative evaluations in both spectral and spatial domains demonstrate that the FSVC-regularized solution still exhibits significantly improved performance relative to diagonal regularization schemes. In the degree range 151–300, the Tongji-GMMG2025S-FSVC model reduces cumulative geoid error degree variances by 9.28 per cent and 9.58 per cent compared to the Tongji-GMMG2025S-KLA and Tongji-GMMG2025S-DSVC solutions, respectively, indicating more effective suppression of medium- to high-degree noise. Spatial comparisons with the XGM2019 model further show reduced gravity anomaly discrepancies, with the FSVC solution achieving the lowest global standard deviation (4.94 mGal). Notably, this improvement is particularly evident in the Indonesia region, which is characterized by complex land-sea distributions. Independent validation using GNSS/Leveling data demonstrates that the FSVC-regularized solution overall higher accuracy than the diagonal-constrained solutions. In particular, the Tongji-GMMG2025S-FSVC model exhibits a distinct advantage, achieving noise reductions of 9.15 per cent and 8.53 per cent relative to the Tongji-GMMG2025S-KLA and Tongji-GMMG2025S-DSVC solutions in the Canadian region, respectively. In conclusion, the proposed FSVC regularization approach proves highly effective in suppressing high-degree noise and enhancing the accuracy of satellite-only static gravity field solutions. This improvement highlights the potential applicability of the proposed approach for future multi-satellite gravity mission integration.

SummaryMachine learning offers new opportunities for geophysical inverse problems, yet conventional regularized inversions of potential field data remain limited by global smoothing constraints and low structural resolution. We propose a locally adaptive, data-driven framework that combines synthetic Earth model generation and ensemble learning for joint gravity and magnetic interpretation. Training models are generated using geologically informed Voronoi-based geometries and planar structures, and a random forest classifier is trained on local statistical features of gravity and magnetic anomalies. The method yields geologically consistent subsurface models that reproduce observed anomaly characteristics without explicit regularization or iterative inversion. Compared with nonlinear Bayesian and traditional regularized inversions applied to the same dataset, the approach provides a substantial reduction in computational cost while preserving key structural features. The performance of the method is inherently linked to how representative the training ensemble is with respect to the target structure, and the results should be interpreted within this context. This framework demonstrates a practical and efficient alternative for potential field inversion using machine learning.

SummaryThis paper describes the implementation of the direct solution method (DSM) using radial spectral elements for the calculation of synthetic seismograms in self-gravitating, spherically symmetric, non-rotating, anelastic, and transversely isotropic Earth models. In contrast to previous implementations of the DSM that used a potential formulation within fluid regions, we use a displacement formulation throughout. It is this feature that allows us to extend the DSM to account fully for self-gravitation along with arbitrary fluid stratification. Our code, DSpecM1D, is benchmarked against the normal mode summation code specnm as well as the direct radial integration code YSpec. Agreement between the codes is excellent for both elastic and anelastic models.

SummaryCarbonate dissolution represents a key mechanism for slab carbon release in oceanic subduction zones. However, the magnitude and controlling factors of carbonate dissolution remain unclear. Here, we develop a coupled thermo-petrological modeling method that integrates slab dehydration, carbonate mineral abundances and their solubilities into subduction-zone thermal models. Systematic model results establish a quantitative relationship between the dissolved CO2 outflux and the subduction-zone thermal parameter (here defined as φ = slab age × subduction velocity/100 in kilometers), which reveals a peak outflux at φ ≈ 13 km, corresponding to warm subduction zones. The dissolved CO2 outflux exhibits a sublinear increase at φ < 13 km and an exponential decline at higher φ. This indicates that warm subduction zones with moderate thermal parameters provide the favorable thermal conditions for carbonate dissolution. The style of aqueous fluid migration strongly influences both the pattern and magnitude of carbonate dissolution. In the pervasive-flow system, fluid infiltration substantially enhances the dissolved CO2 outflux, producing magnitudes approximately three times higher than those in the channelized-flow system. The specific model results for three representative subduction zones—hot Cascadia, warm Nicaragua, and cold Hokkaido—confirm that warm Nicaragua exhibits higher dissolved CO2 outflux, potentially explaining its high arc CO2 degassing outflux.