Geophysical Journal International

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.

SummaryThe Orientale Basin is the youngest and best-preserved multi-ring impact basin on the Moon. It is approximately 930 km in diameter and comprises three concentric rings—the Cordillera, Inner Rook, and Outer Rook rings. We used Gravity Recovery and Interior Laboratory (GRAIL) mission gravity data (GRGM1200B, truncated to degree 660) to invert the three-dimensional (3D) density structure associated with the basin’s mascon and ring-related crustal anomalies. To separate longer and shorter-wavelength signals, we performed inversions using (1) spherical harmonic degrees 2–660 to characterise the basin’s deep structure and (2) degrees 60–660 to highlight crustal-scale heterogeneity. The inversion with degree and order of 2–660 resolves a basin-wide central positive density anomaly beneath the inner depression, extending from a depth of ∼16–80 km, corresponding to uplifted mantle. This anomaly persists below the crust–mantle boundary; however, its deep continuation should be interpreted cautiously because it may partially reflect vertical smearing in the gravity inversion. Nonetheless, the spatial association of this anomaly with a mascon rooted in the upper mantle is compatible with impact-driven uplift of dense material from depth, followed by post-impact thermal evolution and relaxation processes. The inversion with degree and order of 60–660 indicates alternating positive and negative density anomalies associated with the ring system. Prominent ring-parallel positive anomalies occur along the Outer Rook Ring and Cordillera Ring, extending to ∼30–35 km depth and exhibiting a density contrast of ∼60–200 kg/m3. The geometry and lateral continuity of these anomalies across multiple rings support an interpretation of ring-controlled crustal heterogeneity, consistent with either intrusion and structurally focused modification along ring-related discontinuities or impact-generated fracturing that provided pathways for magma ascent. The results of this study provide quantitative constraints on the depth, magnitude, and spatial distribution of density anomalies associated with the Orientale mascon and ring system, thereby improving the subsurface framework for regional geological interpretation and supporting future lunar landing-site geophysical investigations and in situ sampling. Based on the inferred crustal density architecture, we propose that future geophysical sampling efforts should prioritise the Outer Rook Ring and Cordillera Ring, where the observed ring-parallel anomalies may provide insights into crustal modification processes and the composition of the lunar interior.

SummaryWe studied ionospheric changes associated with the 2025 March 28 Myanmar earthquake (Mw7.7) using global navigation satellite system receivers to measure ionospheric electrons, as a part of the project to predict earthquake precursors. The total electron contents above the fault changed their trends ~36 minutes before the earthquake, with the positive anomaly reaching ~1 per cent of the background. These quantities fit well with the past ~20 cases despite relatively large day-to-day variability due to high geomagnetic activities. The positive anomaly was sandwiched by two negative anomalies to the north and the south, suggesting within-ionosphere electron transportation along geomagnetic fields possibly driven by surface positive electric charges released from the fault.

SummaryWe develop and demonstrate a new paradigm for modeling prompt forensics data from potential nuclear explosions of concern. Related scenarios include nuclear terrorism, which may involve low-yield detonations. Traditional modeling appropriate for higher-yield historical nuclear testing is generalized to capture uncertainties in yields (such as when using conversion to obtain “equivalent” nuclear yields for conventional explosives in low-yield experiments) and to capture variation among source-to-sensor path effects for which no calibration data are available. Special attention is paid to quantifying these sources of uncertainty and to their formal inclusion in comprehensive yield uncertainty — uncertainty that would otherwise be underestimated and potentially lead to mistaken conclusions. For the example scenario considered, two useful stand-alone monitoring phenomenologies are based on geophysical data (from surface effects characteristics and local seismic metrics). By fusing signatures from multiple phenomenologies, the Multi-Phenomenology Explosion Monitoring (MultiPEM) framework provides improved yield characterization relative to reliance on single-phenomenology analysis alone, especially when individual sensors have complementary sensitivities to emplacement/environmental conditions.

SummaryBroadband seismic stations are primarily designed to record ground displacement from earthquakes, but they are sensitive to a wide range of processes, including human activity, oceanic waves, and atmospheric pressure variations. These signals are often considered noise, yet their study at frequencies from a few millihertz to one hertz has been fundamental for understanding geosphere coupling, developing methods to image Earth’s interior, and monitoring climate. At lower frequencies, below 10 cycles per day, the origin of continuous seismic noise remains poorly understood and may result from multiple coexisting mechanisms. To illuminate this part of the spectrum and its governing physics, we apply a dedicated processing method to 20 years of global seismic data. Our approach enables precise quantification of frequencies, angular degrees, and velocities of low-frequency modes, which we unambiguously identify as Lamb waves in the atmosphere.

SummaryThe February 6, 2023, Mw 7.8 Kahramanmaraş earthquake reactivated the East Anatolian Fault Zone (EAFZ) and involved surface rupture from the Amik Basin in south to the northeast of Çelikhan in north. Although the EAFZ continues southwest towards the Gulf of İskenderun across the Amanos Mountain Range (AMR) via the Türkoğlu–Osmaniye segment, the 2023 rupture instead followed the western margin of the Karasu Valley. Our analysis suggests that this deviation was governed by structural architecture of these two routes. While both routes involve similar rock units, the AMR is characterized by a massive, intact, and thicker crust that allowed the velocity-strengthening frictional properties of the basement to act as an effective barrier, arresting the rupture east of Türkoğlu. In contrast, the transtensional architecture of the Karasu Valley—evidenced by deep-seated extensional fissures and basaltic volcanism—represents a structurally dilated and thinner crust. This extensional setting neutralized the potential frictional resistance of the basement, providing a rheologically compliant path of least resistance for the 2023 rupture. The Türkoğlu–Osmaniye segment has not experienced a major event for about last 1 500 years and considering a slip rate of ~4.8 mm/yr, about 7 meters of slip deficit has accumulated. Furthermore, the 2023 earthquake loaded stress on the Türkoğlu-Osmaniye Fault. For these reasons, the potential for an M > 7 earthquake on this part of the EAFZ is high, necessitating urgent preparedness for a large earthquake in the region.

SummaryThe Born approximation offers a computationally efficient alternative to full electromagnetic (EM) forward modeling, but suffers from limited accuracy due to its reliance on a fixed background conductivity. In this work, we develop an adaptive Born approximation that treats the background medium as a tunable parameter to enhance accuracy in a goal-oriented manner. The background conductivity is selected locally for each measurement configuration using spatial sensitivity functions, enabling accurate modeling in both isotropic and anisotropic media. In this study, we primarily focus on horizontally layered earth models penetrated by a vertical well to investigate the fundamental behavior of the approximation in a simplified setting. We formulate our approach to be applicable to general anisotropic media by using the Green’s function defined for a homogeneous medium. Furthermore, the approach extends to cases where the background conductivity is isotropic while the actual medium is anisotropic. For a layered medium, the orientation of induced current densities relative to the layering provides physical intuition for background selection, drawing analogies to Voigt- and Reuss-type bounds. While these analogies offer useful guidance, our numerical results do not always conform to the expectations derived from them. Among the averaging schemes evaluated, arithmetic averaging generally yields the most accurate results. Numerical experiments indicate that the adaptive approach significantly outperforms fixed-background models across a range of frequencies, spacings, and conductivity contrasts. Furthermore, an example with a 3D structure illustrates the method’s broader applicability beyond the horizontally-layered earth setting. This framework provides a principled and efficient path toward fast, accurate EM borehole modeling for real-time well geosteering and subsurface electrical imaging.

SummaryThe Southern Apennines—Northern Calabrian boundary is a region marked by lithological heterogeneity, complex geodynamics and tectonics, and prone to significant seismic hazard. This sector is part of a complex geodynamic system, where Africa-Eurasia convergence, Ionian subduction, and slab retreat coexist. Its structure and seismic activity derive from extensive lithospheric heterogeneity and fluid-related processes, both of which are poorly constrained. Here, we present a novel application of seismic attenuation and scattering tomography of the area at a regional scale. We estimated seismic wave attenuation and scattering for the Southern Apennines—Northern Calabria region using a dataset of 1581 waveforms related to 95 M ≥ 3.0 earthquakes that occurred between 2004 and 2024 and were recorded at 32 stations. We constrained the heterogeneous properties and fluid saturation of the Southern Apennines—Northern Calabrian region by mapping P-wave Peak Delays and inverting coda-normalized energies for total attenuation (1/Q). Results consistently reveal different seismic energy dissipation mechanisms between the two domains, reflecting their different characteristics in terms of Peak Delay and attenuation patterns. The Southern Apennines exhibit high Peak Delay values at all depths and almost no remarkable total attenuation anomalies, consistent with weakly consolidated, fractured sedimentary sequences and limited fluid content. Nevertheless, at a depth of 5.4 km, a relatively high attenuation pattern is detectable, likely linked to the presence of less cohesive and potentially fluid-saturated units. Conversely, Northern Calabria shows low Peak Delay and high attenuation in the investigated depth range, reflecting wave propagation through coherent crystalline rocks with significant fluid circulation, likely favored by overpressurized materials or active migration pathways. The spatial correlation between high attenuation, low seismic velocities, and thermal anomalies shows that fluids modulate seismic wave behavior, providing new constraints on the crustal structure and seismotectonic segmentation of the region. The joint interpretation of our results with other geophysical models and responses highlights the complex interplay between lithology, tectonics, and fluid dynamics across this critical segment of the central Mediterranean.

SummaryThe earthquake fault as observed by seismic motion primarily manifests as a surface of displacement discontinuity within a linear elastic continuum. The displacement discontinuity and the surface normal vector (n-vector) of this idealized earthquake source are measured by the tensor of potency, which is seismic moment normalized by stiffness. We exploit this theoretical relation to formulate an inverse problem of reconstructing a smooth, three-dimensional fault surface from an areal density field of the potency tensor. In this problem, the surface is represented by an elevation field that parametrizes the vertical variation of the surface relative to a reference, and the nodal planes of a given potency-density-tensor field describe the n-vector field. The remaining subject is the n-vector-to-elevation transform, the operation inverse to defining the n-vector field on a given surface. Whereas this transform is a well-posed one-to-one mapping in two dimensions where the n-vector has one degree of freedom, the transform becomes overdetermined in three dimensions because the n-vector has two degrees of freedom while the scalar elevation has only one, generally admitting no solution. This overdetermination originates from a reduction in degrees of freedom from six to five upon modeling the source as a displacement discontinuity rather than general potency density, namely inelastic strain. The sixth degree of freedom unmodeled by displacement discontinuities and n-vectors manifests as a local violation of the determinant-free constraint in point potency sources; however, in areal sources of potency density, it raises a conflict with the global consistency of the n-vector field. Recognizing that this conflict derives from the capacity of the potency-density-tensor field to describe inelastic strain source incompatible with displacement discontinuity on a surface, we explicitly introduce an a priori constraint to define the fault surface as the smooth surface that best approximates the surface distribution of inelastic strain by displacement discontinuity. We derive an analytical solution for the surface reconstruction thus formulated and demonstrate its ability to reproduce smooth three-dimensional surfaces from synthetic noisy n-vector fields. Lastly, we integrate the derived formula into the potency density tensor inversion and validate it in an application to the 2013 Balochistan earthquake. The estimated fault geometry agrees better with the observed fault trace than that of the previously proposed quasi-two-dimensional surface reconstruction, highlighting the importance of accounting for three-dimensional fault geometry.

SummarySimulating the behavior of geological materials represents a fundamental objective in geophysical research. To achieve this goal, various models have been developed for different scenarios. While continuum models based on continuum mechanics are most commonly employed, non-continuum approaches such as the discrete element model and the lattice model have also been developed to address the pervasive discontinuities inherent in geological materials. However, existing non-continuum models are predominantly limited to isotropic conditions, significantly constraining their applicability. The dynamic lattice method proposed in this study aims to overcome this limitation. By independently assigning elastic properties to lattice bonds based on their spatial orientation, we have successfully introduced anisotropy into a three-dimensional lattice model. The linear relationships between the lattice model parameters and their continuum counterparts are established in terms of elastic properties. This advanced three-dimensional lattice model has been effectively applied in elastic seismic wave simulations in arbitrary anisotropic media.

SummaryThe singularity points are very common in the low-symmetry anisotropic media. The presence of these points results in complications of the wave fronts (or group velocity images) for waves forming the singularity points. We show the effect of singularity points in multilayered anisotropic media with triclinic symmetry.

SummaryQuantification and control of the in situ mechanics of calcite precipitation in the subsurface are notorious problems often encountered in hydrogeological and engineering applications. Difficulties arise here due to the general inaccessibility and texture of pore spaces, as well as the precipitation reaction’s dependence on fluid chemistry and the composition of the pore surfaces. To mitigate the uncertainties introduced by these inaccessible variables, we propose the use of spectral induced polarization (SIP) as a non-invasive tool to gain insight into the textural and electrochemical parameters controlling the precipitation rate within confined pore spaces and incorporate the gained information into a reactive transport model for quantification. We present SIP monitoring data from three laboratory experiments on diffusive mixing, inducing CaCO3 precipitation in sandstone. During the experimental runs, we identify a clear pattern showing the onset of the chemical reaction in the low-frequency (< 0.1 Hz) response of the imaginary conductivity and the formation of an associated high-frequency peak (> 10 Hz) in the later stages of the experiment. The changes to pore space geometry and precipitation yield were estimated with multiple independent methods. Using information gained from the monitoring data, we predict the dynamics of the precipitation reaction by including textural information, the inner surface area, and the grain size of the precipitate, as well as constraints on the effective diffusivity. These parameters were determined for each sample, based on empirical relations to the polarization response, and incorporated into an accompanying reactive transport model (phreeqc). The experimental results highlight the benefits SIP monitoring can provide to reactive transport models, even if precipitation yield is close to the detection limit of commonly applied methods, such as X-ray powder diffraction or fluorescence.