Journal of Geophysical Research: Solid Earth最新文献

Faults are complex systems embedded in an evolving medium fractured by seismic ruptures. This off-fault damage zone is shown to be thermo-hydro-mechano-chemically coupled to the main fault plane by a growing number of studies. Yet, off-fault medium is still, for the most part, modeled as a purely elastic—hence passive—medium. Using a micromechanical model that accounts for dynamic changes of elastic moduli and inelastic strains related to crack growth, we investigate the depth variation of dynamically triggered off-fault damage and its counter-impact on earthquake slip dynamics. We show that the damage zone, while narrowing with depth, also becomes denser and contrary to prevailing assumptions continues to act as an energy sink, significantly influencing rupture dynamics by stabilizing slip rates. Furthermore, we observe that damage formation markedly reduces rupture velocity and delays, or even prevents, the transition to supershear speeds even for a narrow damage zone. This underscores the critical need to incorporate the complex interplay between the main fault plane and its surrounding medium across the entire seismogenic zone. As a proof of concept, we introduce a 1D spring-slider model that captures bulk elastic variations, by modulating spring stiffness, and normal stress variations that emulate changes in bulk load. This simple model demonstrates the occurrence of slow slip events alongside conventional earthquakes, driven by the dynamic interaction between bulk temporal evolution and fault slip dynamics, without necessitating any changes to frictional properties.

We propose a hierarchical clustering methodology for clustering data from a global navigation satellite system (GNSS) that is applicable at local to global scales. We first adapted the conventional 2D velocity clustering metric for global-scale applications by implementing parallel translation in differential geometry. We then combined it with a Euler-vector-based metric to incorporate the kinematic constraint associated with the rigid motion of plates, achieving advantages in identifying tectonic structures. This hybrid metric approach is assessed through two case studies at different spatial scales to determine whether it can accurately identify tectonic plate and crustal block boundaries: one study uses global-scale data from the ITRF2008 plate motion model, and the other focuses on a local-scale study in Taiwan. Results obtained using the hybrid metric consistently align better with geological data than those from either the 2D or Euler vector-based metrics alone. The proposed method is computationally efficient, enabling us to conduct two types of stability assessment: examination of the robustness of clusters with synthetic noise contamination and leave-one-out analysis. Both tests are demonstrated to be feasible within practical timeframes.

Determining accurate magnetization directions is essential for interpreting magnetic anomalies and inferring the subseafloor crustal magnetization of submarine volcanoes. Furthermore, magnetization directions can be used to determine the polarity of the Earth's magnetic field at the time the seamount was formed, which in turn can be correlated with the geomagnetic polarity time scale to provide independent means of dating submarine volcanic edifices. Here I show a new method to determine seamount magnetization directions from observed magnetic anomalies, based on their fundamental properties expressed by Helbig's infinite integrals, and I propose practical strategies to reduce effects associated with limited-size surveys. The method provides more reliable results than conventional methods based on semi-norm minimization, as demonstrated by the example of Ita Mai Tai Seamount on the Magellan Seamount Trail. The systematic application of this method to the Rano Rahi Seamount Field, in proximity of the East Pacific Rise (EPR) 17°–19°S shows a pattern of alternating crustal magnetization polarities, consistent with few available radiometric ages and with the geomagnetic polarity time scale for the last 3.5 Ma. The corresponding correlation provides an independent tool for dating seamounts in this region, yielding an average constructional volume rate in the range ∼0.5 × 10⁻³–1.3 × 10⁻³ km³/yr for each volcano, which implies a significant contribution of the total magma supply rate is produced off-axis.

Deep-focus earthquakes pose a significant challenge because their occurrence under extreme pressure and temperature conditions should inhibit nucleation through conventional brittle-failure. Transformational faulting is generally accepted as a most plausible mechanism to explain deep-focus seismicity, but it encounters limitations in warm slabs like Nazca because warm temperatures may hinder the preservation of a metastable olivine wedge. Aiming at elucidating the conditions and processes driving deep seismicity in warm slabs, we determined seismic source parameters (stress drop, seismic moment, radiated energy, seismic efficiency) for 13 deep-focus earthquakes (4.8 ≤ Mw ≤ 7.4) in the Peru-Brazil border region. Our results suggest that variations in stress drop can be significant (5–90 MPa) and that scaling between stress drop and seismic moment holds for a wider range of magnitudes (Mw 4.8 to 7.4) than previously reported. Radiated energies are in the 6.8 × 10¹⁰–1.9 × 10¹⁶ J range, with earthquakes in the 6.4–7.4 Mw magnitude range displaying the largest values (4.2 × 10¹⁴–1.9 × 10¹⁶ J). Most importantly, variable radiation efficiencies (0.1–1.4) suggest the coexistence of dissipative and brittle-like ruptures within the slab segment. We propose that these values reflect different degrees of melting involved in the rupture process, possibly controlled by the release of water from hydrous phases in the source region. Moreover, dehydration reactions would be triggered by either the latent heat released from phase transformations or by shear heating, establishing an interplay between thermal runaway enhanced by melting and phase transformations promoted by the release of water.

The ongoing convergence between the Indian and the Eurasian plates has caused significant lithospheric shortening and eastward expansion of the Tibetan Plateau. The Southeastern Tibetan Plateau (SETP), bordered by the Yangtze craton to the east and the subduction of the Indian plate beneath Myanmar to the southwest, plays a crucial role in accommodating this lateral growth. In this study, we construct a new upper mantle S-wave velocity model beneath SETP by jointly inverting broadband (5–140 s) surface wave dispersion curves and teleseismic S-wave traveltimes. Our model reveals two prominent high-velocity anomalies in the upper mantle, differing from previous models' vertical extent. One anomaly beneath the Yangtze craton exhibits a separated two-layered feature; while the other, beneath the South Chuan-Dian Block (SCDB), extends continuously from the uppermost mantle to 300 km depth. These two deep-rooted high-velocity anomalies likely represent mechanically strong blocks modulating the plateau's asthenospheric flow. Two low-velocity features that might be related to such mantle flow are imaged. One is identified at 100–200 km depth near the northwestern Sichuan basin, suggesting potential intrusion of asthenospheric material into the margins of the cratonic lithosphere. The other, a north-south low-velocity channel, is observed at 200–350 km depth beneath the western margin of the SCDB, indicating the southeastward mantle flow may be deflected by plume-enhanced lithosphere beneath the SCDB, or suggesting a component of toroidal flow around the Eastern Himalayan Syntaxis. Our new model has significant implications for understanding the lithosphere-asthenosphere interactions in the Tibetan Plateau and adjacent blocks.

At mid-ocean ridges, volcanic activity is predominantly marked by the voluminous effusion of tholeiitic basaltic lavas, with sporadic occurrences of mildly alkalic basalts. However, the genetic link between voluminous tholeiitic basalts and small-volume alkali basalts remains enigmatic. We report both alkaline and tholeiitic volcanism at the Marion Rise segment of the ultraslow spreading (14 mm/yr) Southwest Indian Ridge (SWIR). In contrast to the effusive tholeiitic (MORB) volcanism in Dr 27 along the Marion Rise, the Dr 30 samples consist of transitional to alkalic glass and alkaline scoria with E-MORB-like affinity (e.g., with high K/Ti, volatile contents (e.g., CO₂ and H₂O), La/Sm and radiogenic heavy isotopes). Critically, the petrological and geochemical evidence of melt inclusions and their host minerals suggests shallow mixing of a volatile-rich low-viscosity alkaline magma with entrained MORB crystal mush. The MORB mush represents a later volatile-poor viscous melt erupted effusively from beneath the axial valley onto the seafloor. This indicates bimodal magmatism beneath ocean ridges with the generation of early-formed alkaline melts that ascend independently of the far more voluminous tholeiites, which then interact and mix in the melt storage region in the ocean lithosphere. Mixing of small volume alkaline melts with more voluminous tholeiitic melts then explains the local major element uniformity of MORB and its isotopic and trace element diversity. We suggest this may apply globally as at magmatically more robust ridges the role of alkali basalt is likely masked by the far more voluminous MORB.

Coral reefs with uniform NE-SW trends are a prominent geological feature along the southern margin of the South China Sea (SCS), closely linked to continental crustal extension. However, their interrelationship and evolution remain inadequately understood. In this study, we present a P-wave velocity model extending from the abyssal basin to the reef areas along the southern SCS margin, derived from forward modeling and travel-time tomography using a 315-km-long wide-angle seismic profile OBS2019ZX1. The results reveal that the crustal thickness beneath the reef areas ranges from 17 to 21 km, with a crustal stretching factor (β) between 1.5 and 1.8, indicating more primitive crustal characteristics. Between the thicker crustal segments beneath the reefs lies an extensional basin, tens of kilometers wide with the thinnest crustal thickness of approximately 13 km and the β exceeding 2.4. We observe strongly heterogeneous crustal extension along the southern SCS margin, where NE-SW trending extensional basins separate thicker crustal segments to form the boudin-like crust. The rifting of the western conjugated margins in the SCS persisted longer and resulted in more complex crustal thinning compared to the eastern region. Crustal extension primarily focused on banded rift basins parallel to the spreading center, leading to the formation of wide rifted margins and dispersed crustal blocks. Under tropical climates, the topographic highs of the blocks exhibit high carbonate productivity, accumulating to form coral reefs. We propose that boudin-like crustal extension is a key factor controlling the formation of elongated NE-SW trending coral reefs along the southern SCS margin.

We aimed to establish how permeability heterogeneities develop in relation to compaction deformation in sandstone. Three sandstones were tested in the compactant regime: Locharbriggs sandstone, which is initially heterogeneous with beds of lower initial permeability; a low porosity (22%) Bleurswiller sandstone, which is initially homogeneous and produces localized compaction bands; a high porosity (24%) Bleurswiller sandstone, also homogeneous but producing compaction in a more diffused pattern. We monitored acoustic emission locations and elastic wave speed variations throughout deformation. In addition, at regular stages during each test, a constant pore pressure difference was imposed at the boundaries of the samples, and steady-state flow was established. Internal pore pressure measurements at four locations allowed us to derive local permeability estimates. In all samples, progressive compaction produced overall reductions in permeability. In addition, localized compaction also produced internal reorganization of the permeability structure. Strong permeability reductions in the direction perpendicular to flow, by up to two orders of magnitude, are only observed when fully connected compaction bands grow across samples. Compaction and permeability reduction preferentially impacted the more porous and permeable regions of the samples, which lead to an overall homogenization of the transport properties of the samples during deformation. Compaction results from grain crushing, and is directly linked to progressive reductions in elastic wave speed. However, the impact of compaction on permeability depends strongly on the spatial connectivity of the compacted regions.

This study addresses a significant gap in understanding the features of the south-central Cascadia subduction zone, a region characterized by complex geologic, tectonic, and seismic transitions both offshore and onshore. Unlike other segments along this margin, this area lacks a 3-D velocity model to delineate its structural and geological features on a fine scale. To address this void, we developed a high-resolution 3-D P-wave velocity model using active source seismic data from ship-borne seismic shots recorded on temporary and permanent onshore seismic stations and ocean-bottom seismometers. Our model shows velocity variations across the region with distinct velocity-depth profiles for the Siletz, Franciscan, and Klamath terranes in the overlying plate. We identified seaward dipping high-velocity static backstops associated with the Siletz and Klamath terranes, situated near the shoreline and further inland, respectively. Regions of reduced crustal velocity are associated with crustal faults. Moreover, there is significant along-strike depth variation in the subducting slab, which is about 4 km deeper near the thick, dense Siletz terrane and becomes shallower near the predominantly less-dense Franciscan terrane. This highlights a sudden tectonic and geologic transition at the southern boundary of the Siletz terrane. Our velocity model also indicates slightly increased hydration, though still minimal, in both the oceanic crust and the upper mantle of the subducting plate compared to other parts of the margin.