Journal of Geophysical Research: Solid Earth最新文献

The incorporation of water in high-pressure minerals is essential for the water cycle within the interiors of terrestrial planets. Majoritic garnet, a major component in the mantles of Earth and Mars, plays a significant role in this context. In this study, we use first-principles simulations to explore water incorporation mechanisms in MgSiO₃-majorite, which is a key end-member of majoritic garnet, at conditions up to 2,000 K and 20 GPa. By dealing with the relationship between chemical potential and the Gibbs free energy changes for the reactions at equilibrium conditions, we determine the ratios of the seven potential hydrous defects. Our results reveal that the Si2 and Si3 defects, which are of the hydrogarnet-type, dominate water incorporation in MgSiO₃-majorite. In addition, we evaluate the effects of these hydrous defects on seismic wave velocities. The presence of Si2 and Si3 defects, with an expected water concentration of ∼700 ppm, has a small effect on both P-wave and S-wave velocities. Nevertheless, the influence of water on lateral variations in the seismic wave velocities of MgSiO₃-majorite, which is opposite to that found for ringwoodite, offers a potential tool for investigating compositional heterogeneities in hydrated regions of planetary mantles.

Variations in the paleointensity of the Earth's magnetic field are intrinsically linked to the evolution of planetary interior dynamics and surface environmental conditions. However, the reliability of absolute paleointensity experiments is often compromised by the non-ideal magnetic behavior of multi-domain grains and alteration of magnetic minerals. To mitigate these challenges, besides conventional rock magnetic methods, this study also employs Visible and Near-Infrared Reflectance (VNIR) spectroscopy as a rapid screening tool to identify thermally unstable mineral phases that can distort experimental results. Systematic rock magnetic analyses reveal that samples with more pronounced single-domain-like magnetic properties achieve significantly higher success rates in paleointensity experiments. The implementation of VNIR-based screening increased the average success rate of analyzed samples by a factor of 1.9 compared to magnetic selection alone. We recommend using VNIR screening with M_rs/M_s ≥ 0.16 as the sample selection criterion, which can increase the success rate threefold while maintaining sufficient sample availability. By integrating VNIR spectroscopy with conventional rock magnetic methodologies, this study presents a robust approach to enhance the reliability and success rates of paleointensity determinations.

Seismic reflection and bathymetry collected along the Ecuador–Colombia obliquely convergent margin allow the first characterization of the NNE-trending, near-trench strike-slip Ancon Fault in the possible source region of the 1906-Mw8.6–8.8 and 1979-Mw8.2 earthquakes, which produced devastating tsunamis. This study aims at highlighting the possible tsunami contribution of the fault during subduction earthquakes. The fault, which correlates with a zone of strong interseismic, inter-plate coupling, is 200-km-long, segmented and bordered by remarkable slump scars. It bounds a tectonic sliver characterized by structural and rheological variations. The south-fault segment bounds a pop-up structure that comprises an up-to-25-km-wide accretionary wedge, and a mid-slope oceanic basement block uplifted by dextral transpression. The Ancon Fault becomes dominantly reverse in a seamount collision zone, where the East-directed Galera fault takes over toward the central-fault segment. This segment shows extension reflecting a releasing fault bend. The northern-fault segment is transpressive and fans out northward. It separates the fore-arc basin from a near-trench, ∼20-km-wide, pop-up oceanic basement block. Morphology, geological structures and sediment dating support a late-Pleistocene/Holocene activity of the Ancon Fault. The fault could have ruptured concurrently with the 1906 and possibly 1979 earthquakes, and contributed to the tsunamis by producing lateral displacement and differential uplift of the tectonic sliver in a similar way as a normal fault rupture contributed to the 2011 Tohoku-Oki tsunami. Transpressional uplift and landslides associated with the rupture of strike-slip faults are plausible contributing factors to tsunamis offshore North Ecuador-South Colombia and should be considered in seismic hazard models.

The mechanisms of complex Moho reflections at fast- and intermediate-spreading ridges remain unclear. A potential key factor is hydrothermal activity, which at mid-ocean ridges may result in serpentinization of peridotites under the stability field of antigorite (400–600°C) or chrysotile-lizardite (<400°C). Here, we calibrated the relationship between serpentinization degree, density, and seismic velocities of peridotites at 200 MPa. Based on physical properties of rocks in the oceanic lithosphere, we established seismic velocity and density models of a sharp or layered crust-mantle boundary with different serpentinization types. Synthetic seismograms demonstrate that the oceanic Moho reflections are controlled by both structure and serpentinization of the crust-mantle boundary. The impulsive Moho may correspond to a sharp mafic-ultramafic boundary (petrological Moho) with <10% serpentinization, or the bottom of 60%–80% antigorite peridotites. The Moho reflection becomes invisible when antigorite percentage decreases from 60%–80% (top) to 0% (bottom) in the uppermost mantle for a sharp mafic-ultramafic boundary. Besides the layered crust-mantle boundary, the diffusive Moho could also result from the sharp mafic-ultramafic boundary with 10%–60% or 80%–100% antigorite peridotites, or chrysotile-lizardite peridotites overlying antigorite peridotites. Using synthetic seismograms, the diffusive Moho at 6–9 km to the west of the East Pacific Rise 9°44′N can be interpreted by 30% antigorite peridotites, suggesting localized hydrothermal circulation close to the fast-spreading mid-ocean ridges. Moho reflections and wide-angle PmP waveforms at mid-ocean ridges can provide new clues to decipher the interplay between magmatic, tectonic, and hydrothermal processes in the oceanic lithosphere.

Whether seismicity is correlated with the solid Earth tides has been a longstanding problem, but the findings remain ambiguous. The attempts at its resolution shed light on the physical properties and processes controlling earthquake triggering. The recent surge in earthquake data and advancement in detection techniques provide an opportunity to revisit this problem. We utilize a 40-year Southern California Seismic Network catalog and a 10-year Quake Template Matching catalog to explore the tidal modulation in Southern California. Results indicate that the correlations between earthquakes and tides vary with location. Regions where seismicity is significantly modulated by tidal stresses have relatively low effective background normal stress (20–155 kPa), which are primarily associated with geothermal locations. Additionally, deeper earthquakes in certain areas have a stronger correlation with tides. These phenomena suggest that faults with lower effective background stress might be more sensitive to tidal modulation. Furthermore, earthquakes of specific types (strike-slip and thrust) in certain areas are more likely to correlate with tides, suggesting that different fault types experience different tidal loading amplitudes. Our study suggests that earthquake catalogs covering longer time spans with smaller completeness magnitude are required for more robust tidal modulation analysis, and the modulation of seismicity by tides provides a probe to measure the effective background normal stress on the faults at depth.

Understanding the architecture and kinematics of intersecting fault systems concealed beneath megacities is crucial for seismic hazard assessment and the mitigation of associated geohazard. Here, We present high-resolution 3D seismic reflection data that provide the first direct evidence for kinematic supersession between two major conjugate faults beneath the Beijing Plain in the North China Craton (NCC). This analysis reveals a fundamental tectonic reorganization around the Middle Pleistocene boundary (∼0.78 Ma), where a regional stress field shift from NE-SW extension to ∼E-W compression transferred strain accommodation from the Huangzhuang-Gaoliying Fault (HGF) to the more favorably oriented Nankou-Sunhe Fault (NSF). This shift initiated left-lateral transtensional motion on the NSF, which now demonstrably truncates the HGF, establishing it as the primary contemporary seismic source—a conclusion supported by a displaced paleochannel and a distinct growth fold. This kinematic transfer resolves the long-standing paradox of major ground fissures overlying the now seismically quiescent HGF. We propose a multi-scale “bookshelf faulting” model, wherein aseismic tensional reactivation of the HGF—driven by shear on the master NSF—is dramatically amplified by anthropogenic land subsidence. This work provides a detailed model for strain partitioning and fault system evolution in an intraplate setting, offering essential constraints for seismic hazard models in Beijing and a transferable framework for other megacities built upon similarly complex fault networks.

Basin inversion, involving the transition from extensional to compressional stress, has been extensively studied. Traditional theories predict uplift and erosion of extensional basin structures during inversion, yet some rifted basins, like the Pannonian Basin in southeastern Central Europe and the Pearl River Mouth Basin (PRMB) in the Northern South China Sea (SCS) show sustained subsidence even under compression. Previous sandbox experiments and numerical models mostly focus on fault inversion at the scale of sedimentary basins and overlook large-scale boundary conditions, such as compression from subduction initiation. Here, we investigate the anomalous subsidence in the PRMB, adjacent to the SCS and the Manila Subduction Zone. Using two-dimensional numerical models and varying basin wavelength and thickness, and the convergence velocity of the upper plate to explore how rifted basin responses to the subduction. Our results show that subduction initiation can sustain central basin subsidence for >1 Myr, with high tectonic subsidence rates (>0.4 mm/yr) despite compression. The lithosphere undergoes both lithospheric- and crustal-scale buckling; the latter dominates when inherited structure has short wavelength, enhancing distributed deformation and broadening the subsiding area. Basin subsidence exhibits a periodic feature, including a “reactivation stage” with high tectonic subsidence rate triggered by subduction initiation. The inherited boudinage structure promotes distributed deformation and tectonic subsidence, while subduction velocity enhances the overall subsidence rate. The characteristic wavelength of deformation depends primarily on inherited structure and lateral variations in lithospheric strength. Overall, our results emphasize the importance of subduction induced compression and the inherited structure on basin inversion.

Sotará is a little-known andesitic-dacitic stratovolcano in southwestern Colombia. Although there are no recorded historical eruptions, the volcano shows clear evidence of geothermal activity, deformation, and volcano-tectonic seismicity. Its remote location and rugged terrain pose challenges for access and routine monitoring. The application of satellite geodesy, specifically continuous GNSS and DInSAR, has enabled effective monitoring of unrest in this hard-to-reach area. During 2017–2018 and 2019–2020, a subtle yet distinct volcanic deformation was observed by GNSS and InSAR. Initially, about 1.5 cm of uplift was observed prior to any increase in seismic activity. Subsequently, an increase in volcano-tectonic seismicity was followed by additional uplift of around 2.5 cm. Modeling of the observed deformation suggests the injection of small magma batches beneath the volcano: 0.0003─0.0022 km³ at depths of 1.2─3.9 km in 2017–2018, and 0.0003─0.0017 km³ at similar depths in 2019–2020. Neither episode culminated in an eruption, and both seismicity and deformation returned to background levels by February 2020. The observed unrest patterns offer empirical constraints on the behavior of shallow magmatic systems in the Northern Andes, an area that remains less well represented in volcano deformation data sets. The small magma volumes and limited uplift reflect episodic magma replenishment in a long-dormant volcanic system, consistent with models of tectonically modulated magma ascent along the Andean margin. These findings strengthen regional comparisons with better-studied Andean volcanoes (e.g., Sabancaya or Nevado del Ruiz), helping to build a more unified understanding of arc volcanism and magma plumbing systems.