Journal of Geophysical Research: Solid Earth最新文献

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.

Volcanic eruptions are currently understood as triggered by increases in the overpressure of the magma storage regions, usually resulting in ground deformation. We assess whether observations of ground deformation can provide insights on the triggering mechanisms of sub-Plinian and Plinian eruptions, which are the most hazardous eruptions with a global impact. We process and compile InSAR and GNSS time series from 1991 to 2025 spanning four eruptions of this type in the Southern Andes: Hudson 1991, Chaitén 2008–2009, Cordón Caulle 2011–2012 and Calbuco 2015, resulting in the subduction zone with the largest erupted mass during 1980–2019. Only Cordón Caulle displays the theoretical pattern of pre-eruptive uplift due to reservoir pressurization, co-eruptive subsidence due to magma extraction, and post-eruptive uplift in response to magma inflow. For the rest of the volcanoes, we observe co- or post-eruptive ground deformation, but the data temporal resolution is low and did not sample well all the eruptions. On a global scale, InSAR and GNSS data recorded at volcanoes in subduction zones that experienced similar eruptions indicate few well-recorded eruptions. Only Okmok records a similar pattern to that of Cordon Caulle, while in other volcanoes geodetic data recorded the last episodes of pre-eruptive reservoir pressurization. This implies that most of the magma that increased the overpressure could have been emplaced in the decades or centuries prior to eruption and geodetic observations, or emplaced undetected. The longer time scales of recharge in subduction zone volcanoes compared with basaltic volcanoes in hot spots could indicate larger storage regions.

Seismicity during non-eruptive periods is useful for observing stress changes related to magmatic transport and volatile exsolution within active volcanoes. Mount St. Helens in Washington, USA, is the most active volcano in the continental United States and has been in quiescence since 2008. To explore the processes driving seismicity at Mount St. Helens, we create a high-resolution seismicity catalog of non-eruptive seismicity from 2008 through 2023, consisting of 31,133 events. We find persistent shallow seismicity (−2.2 to 2 km below sea level (BSL), 0–4.2 km below the surface) throughout the entire study period that concentrates beneath the dacite dome complex from the 1980–1986 and 2004–2008 eruptions. Additionally, there is frequent deeper seismicity (2–8 km BSL, 4.2–12.2 km below the surface) beginning in 2016. We examine a selection of deep earthquake swarms and find complex along-depth seismicity patterns. Within swarms, increases in shallow seismicity rates can precede or are concurrent with increases of deep seismicity rates. Lastly, we discover a series of semi-periodic, shallow, burst-like swarms, consisting of low-amplitude, repetitive similar earthquakes, indicating periodic valve-like release of fluid pressure from the conduit. Increased seismic activity beginning in 2016 indicates ongoing repressurization within the magmatic system driven by recharge or crystallization-induced second boiling within the upper-crustal reservoir after 2008. The data indicate that non-eruptive seismicity at Mount St. Helens is controlled by fluid pressure changes from gas flux sourced from the magma reservoir that migrates through crack networks.