Journal of Geophysical Research: Solid Earth最新文献

The b-value, defined as the slope of the cumulative earthquake frequency–magnitude distribution in semi-logarithmic space, quantifies the relative occurrence of small and large earthquakes. It is a key metric for hazard assessment and is often used in adaptive traffic light systems to mitigate induced seismicity. In this study, we analyze a 4-year sequence of induced earthquakes at the Vendenheim geothermal site near Strasbourg (France), where multiple sequential operations were carried out near a regional fault zone, to explore the spatio-temporal variability of the b-value during fault activity. Our analysis highlights the importance of spatial clustering in understanding b-value variability. Despite occurring in close spatial and temporal proximity, seismicity clusters exhibit markedly different b-values. The clusters with the lowest b-values host the largest magnitude events (). Even when significant seismic migration is observed within the clusters, their b-value remains relatively constant over time. The observed temporal fluctuations in the b-value of the entire induced seismicity population are shown to be closely related to the relative activity of each cluster over time. We propose that b-value variations, along with the observed seismicity migration, are related to inherited spatial variability in the geomechanical properties of faults rather than to the dynamic evolution of stress conditions.

Studying geodynamic processes at the plate-mantle interface requires knowledge of how plates move over and subduct into the mantle. The absolute motion of plates relative to the mantle since ∼120 Ma is classically estimated using hotspot tracks. However, for older times only hybrid frames are available that integrate multiple types of constraints, such as trench kinematics, plate velocity, net lithosphere rotation, true polar wander, and eruptions of kimberlites and large igneous provinces. This diminishes the number of independent constraints that we can use to learn about geodynamic processes. Here, we compute absolute plate motions by minimizing absolute continent velocity in a global plate model, in 10 Ma timesteps back to 1 Ga, assuming that continental keels resist relative continent-mantle motion. We estimate uncertainty by adding a ±5 Ma temporal uncertainty to each step and find absolute plate motion is reliable for the last 350 Ma, but not before. The “continent frame” predicts a Cretaceous episode of high net lithosphere rotation due to fast Izanagi plate motion that may signal an anomalously weak NW Pacific upper mantle. Furthermore, the continent frame predicts that Indo-Atlantic hotspots moved parallel to the edges of large low shear velocity provinces and kimberlite eruption sites moved parallel to plate motion. We show that by constructing a global absolute plate motion model based on one assumption, minimal continent motion, allows placing the mantle in a plate tectonic reference frame and unlocks all other constraints of plate-mantle interaction to kinematically reconstruct mantle convection.

The Alpine-Himalayan belt is one of Earth's most dynamic and complex regions, characterized by intense tectonic deformation and seismicity. Comprehensive analyses of continental-scale crustal deformation and seismic hazards along this extensive orogenic belt require the compilation of large geodetic data sets. In this study, we integrate 42 published Global Navigation Satellite System (GNSS) velocity fields, building an internally consistent data set for the entire belt, spanning from Iberia to Southeast Asia and comprising 11,177 horizontal and 3,940 vertical velocities. We use this unified GNSS velocity field to estimate surface strain rates and their posterior uncertainties in the eastern Mediterranean region and the India-Asia collision zone. Our results show large-scale agreement between the orientation and style of geodetic and seismic strain rate tensors across the belt. Additionally, our analyses substantiate previously documented azimuthal alignments between principal strain rate directions and seismic anisotropy orientations, often used as a proxy for finite strain in the convecting mantle. These correlations are particularly apparent in the Aegean, North Anatolia, Tibet, Tian Shan, Altai, Sayan, and Baikal regions, underscoring the need for future research on the relationship between mantle flow and lithospheric deformation.

Most volcanoes exhibit circular or elliptical shapes, and volcanic cones in sedimentary basins along continental margins typically have irregular distributions. However, the continental margin of the South China Sea (SCS) hosts a unique feature: linear volcanic constructs surrounding the rigid Xisha Massif. These constructs are interpreted as the products of fissure eruptions, focused along underlying fault systems. We studied their distribution and characteristics using multibeam bathymetric data, 2D seismic profiles, and gravity/magnetic data sets. Our results show that these faults are formed in response to the incipient counter-clockwise rotation of the rigid Xisha Massif during the Late Oligocene to Early Miocene—a rotation triggered by interaction with the southeastward-escaping Indochina Block. This rotation generated faults with unusual orientations in the weak zones surrounding the massif, which were later exploited by magma to form the observed linear volcanic constructs. This study represents the first inference of incipient counter-clockwise rotation of the Xisha Massif. It further reveals that the escape of Indochina Block exerted profound, long-lasting influences on the stress field, faults activity and magmatism of the western SCS, persisting even after escape-related motions ceased. More importantly, this work documents a case of en-echelon linear volcanic constructs in a sedimentary basin, advancing the tectonic interpretive value of such features for intraplate shear extension and micro-block interactions. The results may also be applicable to other areas with similar geological settings.

The thermal conductivity (κ) and thermal diffusivity (D) of two types of Himalayan leucogranite were measured using a transient plane-source method in a temperatures range of 298–1173 K and pressures of 0.5–1.5 GPa. Both the κ and D of leucogranites have a positive correlation with pressure. With increasing temperature, D initially decreases rapidly and then stabilizes. At temperatures below 973 K, κ decreases with temperature, after which it increases with temperature. The biotite in the recovered samples underwent dehydration-melting reaction. The increase of κ at high temperatures (>973 K) may be attributed to the aqueous melt produced by the reaction, which correlates positively with the content of biotite. Lithosphere thermal modeling in the Himalayan orogenic belt indicates that the Himalayan crust exhibits a high geothermal gradient. The dehydration of muscovite may be the primary mechanism resulting in partial melting of the upper and middle crust to produce leucogranite melts. During the decompression process, dehydration of amphibole may provide deep water sources.

Hydrothermal systems in volcanic-evaporitic environments provide unique insights into subsurface geological processes, yet their magnetic signature remains poorly understood. Here we suggest that hydrothermal activity in the Dallol area of Ethiopia produces distinct magnetic patterns that may reflect both physical and chemical modifications of the subsurface. Through high-resolution near-surface magnetic surveys, we identify weak positive anomalies associated with reddish brine mud layer and negative amplitude anomalies (∼20 nT) over active hydrothermal features. These patterns suggest that hydrothermalism consistently results in weakening magnetization through mechanical destruction and chemical alteration of substrates, providing insights into fluid circulation and their relationship with tectonic processes. Our findings support that near-surface magnetic surveys can effectively map active hydrothermal systems across diverse geological settings from volcanic-evaporitic environments to mid-ocean ridges with important implications for understanding geothermal exploration, and the evolution of divergent plate boundaries.

The hydraulic and rheological properties of shear zones that develop in dome-building eruptions govern the potential for explosive and seismic behavior at those volcanoes. Previous isostatic hot-pressing experiments demonstrated that crystalline fault gouge undergoes solid-state sintering at high temperature and pressure, and sintering causes lithification and permeability loss within volcanic shear zones over years. We present results of torsion experiments in which we document, for the first time, gouge rheological behavior at the temperature-normal stress-strain rate conditions expected in volcanic shear zones, and determine the effect of shear on solid-state sintering rate. Gouge sheared at 500°C, 50 or 100 MPa normal stress and 10⁻⁴ to 10⁻³ s⁻¹ does not sinter, exhibits strain-independent behavior, and deforms by distributed granular flow. In contrast, gouge sheared at 900°C, 50 or 100 MPa normal stress and 10⁻⁵ to 10⁻³ s⁻¹ sinters, strain-weakens, and exhibits microstructural evidence of strain localization and significant lithification. Samples sheared at 900°C for <1 hr have final porosities and permeabilities comparable to gouge samples hot-pressed for 60 hr, indicating sintering is enhanced by a shear stress acting on grain boundaries in addition to a normal stress. These results are used to develop a model for time-dependent densification by solid-state sintering that is applicable when gouge is static or shearing. Finally, we propose that sintering-driven lithification can cause deforming shear zones to transition from aseismic stable sliding to seismogenic sliding, potentially resulting in the drumbeat seismicity frequently observed at dome-building volcanoes.

A devastating M_W 7.4 earthquake struck the northern Longitudinal Valley in eastern Taiwan on 3 April 2024. The intense and prolonged aftershock sequence over the following month exposed both the region's tectonic complexity and the challenge of timely earthquake cataloging. Gaps in the initial catalog from the local agency revealed short-term incompleteness, potentially delaying critical hazard assessments and emphasizing the need for more efficient data-processing workflows. To address this issue, we developed an automated workflow, AutoQuake, which processes continuous waveform data using machine learning (ML) models and seismological algorithms. AutoQuake integrates phase picking, phase association, 3-D double-difference relocation, local magnitude estimation, and focal mechanism determination within a flexible Python interface that allows user customization. The resulting ML-enhanced event and focal mechanism catalogs are five times larger than the local agency catalog and 10 times larger than the moment tensor inversion catalogs. The 2024 Hualien earthquake sequence revealed by AutoQuake complements the 2018–2021 seismicity in spatial distribution and resolves detailed fault interactions between the Central Range Fault (CRF) and the Longitudinal Valley Fault (LVF) systems, including a newly-developed deep west-dipping fault and an east-dipping fault parallel to the LVF. These features suggest an evolving system of conjugate faulting that accommodates the high convergence rate along the plate boundary (∼30–40 mm/yr). This study demonstrates the potential of ML-based workflows to efficiently process large volumes of seismic data, enabling timely responses to major earthquake sequences and offering new insights into the complex seismogenic structures in the tectonic transition from collision to subduction.