Tectonophysics最新文献

Although drilled samples of fault rocks have yielded information on frictional features of shallow subduction zones, the relationship of rupture propagation to the levels of friction and pore-fluid pressure remains uncertain. To investigate this topic, we performed dynamic rupture simulations along the megasplay fault that slipped during the 1944 M_w 8.0 Tonankai earthquake in the Nankai Trough. We used actual data from friction experiments on rocks from the fault segment and pre-existing pore pressures deduced from geophysical surveys for the shallow portion of 0–10 km depth along the fault. Simulations of low friction (friction coefficient ca. 0.04) produced large slip (about 30 m), whereas simulations using higher friction (friction coefficient ca. 0.2) suppressed the rupture. In simulations with low friction in which the pore-fluid pressure was nearly equal to the lithostatic stress, the slip decreased to about 25 m. However, when the simulations included slip-strengthening at shallow depth and higher friction, the slip still reached roughly 20 m. Such variability in slip during rupture propagation is caused by differences in the friction features and fluid pressure conditions of fault rocks, in which the friction features might be related to the mineral composition. Spatiotemporal heterogeneity in fault-rock type and their physical and hydraulic properties may fundamentally produce the complexity and variability of earthquake rupture propagation along the Nankai plate-subduction boundary.

Detachment faulting related to oceanic core complexes (OCCs) has been suggested to be a manifestation of slow seafloor spreading. Although numerical models suggest OCCs form under low magma supply, the specific interaction between magmatism and tectonic faulting remains elusive. This paper examines seismic observations detailing the spatiotemporal interactions between magmatism, high-angle faulting, and detachment faulting at a slow-spreading mid-ocean ridge in the West Philippine Basin. We identified a magma-rich spreading phase, indicated by a magmatic top basement and oceanic crust with shallow-penetrating high-angle normal faults. An axial valley reveals an along-strike transition from magmatically-dominated to highly tectonized oceanic crust over a distance of 70 km. Two older OCCs with concave-down fault geometries and a younger OCC with steep-dipping faulting suggest sequential detachments with the same polarity. Our findings suggest: (1) slow seafloor spreading alternates between high-angle faulting with a relatively high magma supply and detachment faulting with a limited magma supply; (2) sequential development of younger detachments in the footwall of its predecessor leads to an asymmetric split in the newly accreted crust; and (3) the life cycle of OCC ends with high-angle faults that overprint the detachment and act as magma pathways, sealing the OCC. Our study captures the dynamic interaction between high-angle and detachment faults and their concurrent and subsequent relationship to magmatic systems. This reveals that strain distribution along strike is critical to OCC formation, thus enriching our understanding beyond conventional considerations such as spreading rates and melt budgets at mid-ocean ridges.

Continental rifts normally initiate within previously deformed lithosphere and thus their evolution and architecture can be largely controlled by inherited weak zones in the pre-rift crust. Here, we quantify the role of the strength and obliquity of pre-existing crustal-scale weak zones in the evolution of continental rift systems. We use a 3D numerical geodynamic model to assess strain localization, associated fault development, and rift segmentation during the early stages of tectonic extension. We find that both the strength and obliquity of the weak zones significantly influence the patterns of strain localization. A pre-existing very weak zone with low obliquity can promote the development of continuous and long-lived border faults parallel to the rift axis. Conversely, a comparatively strong weak zone with high obliquity leads to a staggered en-echelon rift geometry that lacks rectilinear laterally persistent strain localization. Furthermore, we find that rift obliquity and weak zone strength may modulate rift fault length, throw, and azimuth. These results provide new and compelling insights into the structure and evolution of natural active rifts that develop within orogenic basement terranes.

Reactivation processes play a significative role in the localization of deformation but still remain hard to establish at the lithospheric scale. In this work, we built a 3D structural model, which enables to bridge the gap between the main tectonic structures observed at the surface and the geometry of the major interfaces (the Mohorovičić-discontinuity (hereafter Moho) and top of the basement) inferred from geophysical data acquired in the external Western Alps and their foreland. The geometry of these tectonic structures is interpreted in relation to their geodynamic evolution. The main results of this study highlight: (1) a strong contribution of thick-skinned Pyrenean-Provence and Alpine tectonics, (2) a lithospheric rooting of Variscan shear zones and related faults, and (3) the regional-scale influence of these inherited structures on the post-Paleozoic strain localization in the study area. Our 3D model shows that the pattern of Variscan shear zones that were developed at the end of the Paleozoic involved the whole crust, as emphasized by the Moho offsets. These shear zones were reactivated and localized Meso-Cenozoic deformation. The Variscan deformation pattern controlled the geometry of extensional basins, the propagation of Pyrenean-Provence deformation, and finally the Alpine deformation at crustal scale. Our 3D model shows minor crustal thickening (ca. 40 km) located below the Pelvoux External Crystalline Massif, which probably resulted from both Pyrenean and Alpine tectonic phases. In contrast, the southern part of the Alpine front shows a thinned crust (ca. 18 km) resulting from extensional Meso-Cenozoic phases between the Cévennes margin and the Durance basin.

The Barreirinhas pull-apart system encompasses marginal basins in divergent and transform margin segments in the central sector of the Brazilian Equatorial Margin and its African conjugate counterpart. This ancient pull-apart system evolved through transtensional strike-slip motion within a highly heterogeneous crystalline basement affected by multiple rift phases. The geometry and development of pull-apart structural elements during the final rifting phase before continental breakup and the mechanisms and extent to which they were influenced by preexisting crustal heterogeneities are comprehensively addressed using an extensive database of potential field (magnetic and gravity) and 2D seismic reflection data. We also assess the lithospheric thermomechanical conditions and their influence on transtensional extension throughout Curie Point Depth, Heat Flow, and Moho depth, derived from potential field data and published seismological models. Plate reconstruction of Brazilian and African equatorial margins based on gravity patterns and comparison with sandbox analog models allow a 3D synoptic model to reveal the Barreirinhas pull-apart system evolution during the Equatorial Atlantic opening. During the rift phase I, the location of major grabens was controlled by favorably oriented Neoproterozoic shear zones, while the cooler, stronger, and thicker crust beneath cratonic areas formed the western barrier to strike-slip rift activity during rift phase II. This same geological domain anchored the onset of the pull-apart system in the last rift phase III, whose principal displacement zones developed along the extensive oceanic fracture zones linked by sigmoidal fault systems. Toward the end of the rift phase, a large asymmetric lozangle to a lazy-Z-shaped, pull-apart basin developed above low overlapping ∼90°, releasing stepover in oblique transtensional strike-slip motion.

On 22 May 2021, an M_W 7.4 earthquake occurred in Maduo County, Qinghai Province, China, which is located on the Kunlun Mountain Pass-Jiangcuo fault inside the Bayan Har block, providing a good opportunity to investigate seismogenesis of large intraplate earthquakes. We analyze two years of continuous seismic data from June 2021 to June 2023, which were recorded at 34 portable seismic stations of the MaduoArray deployed in the source zone by our group. The LOC-FLOW workflow of automatic detection and location is applied to construct a complete and high-precision seismic catalog for the region, which includes machine-learning phase picking (PhaseNet), earthquake phase association (REAL), velocity model updating and station correction (VELEST), absolute earthquake location (HypoInverse), and relative location (HypoDD). As a result, 78,832 Maduo aftershocks and other local earthquakes are detected and relocated precisely. Our results show that the length of the Maduo aftershock zone is ∼170 km, which is mainly distributed along the NWW-SEE oriented Kunlun Mountain Pass-Jiangcuo fault, and there is a horsetail bifurcation feature at the eastern end of the aftershock sequence. The seismogenic fault is nearly vertical, and local seismicity occurs on both sides of the fault. Our results also show that there is no seismic gap or aftershock sparse area in the region. Previous studies have revealed a low-velocity and high-conductivity anomaly below the source zone, reflecting fluids ascending from the lower crustal flow. These results provide new insights into the cause of the 2021 Maduo earthquake.

The Mexican subduction system is an ideal region to study 3-D mantle deformation patterns in response to changes in slab geometry and the presence of tears. Shear-wave splitting measurements were made using SKS, SKKS, and PKS waves in southern Mexico, where the Cocos slab subducts beneath the North American and western Caribbean plates. For most of southern Mexico, the results are consistent with predominantly trench-normal fast polarization directions that can be interpreted as a consequence of sub-slab entrained flow and 2-D corner flow in the mantle wedge in the presence of A-type olivine fabric (or similar). This pattern of trench-perpendicular fast axes extends northward to the region southeast of the Trans-Mexican Volcanic Belt. Beneath its eastern end, fast axes rotate ∼20° clockwise and are likely controlled by the absolute motion of the North American plate. In southeastern Mexico, along the coast and above the mantle wedge tip, the fast axes are trench-normal and the delay times are the shortest. They were interpreted to result from a possibly serpentinized mantle wedge tip. In the same region above the mantle wedge core, the splitting parameters appear to result from different flow patterns in the mantle wedge and the sub-slab mantle.

High-pressure and temperature deformation experiments interfaced with acoustic emission (AE) monitoring have been conducted to study transformational faulting in Mn₂GeO₄ olivine, which transforms to the β phase, isostructural to wadsleyite. Metastable Mn₂GeO₄ olivine exhibits a marked embrittlement behavior at temperatures between 800 and 1100 K, emitting numerous AEs. At each temperature, brittle deformation is characterized by a two-stage process: (1) a “preparation” stage with numerous diffusedly located low-magnitude AEs and large b values (>2), and (2) a failure stage where larger-magnitude AEs form a planar distribution with b values about 1. Microstructure analysis reveals extensive kink band development in olivine grains in the recovered samples. Kink band boundaries (KBBs), with a typical thickness of ∼100 nm, are filled with a nanometric β-Mn₂GeO₄ “gouge”. A dense array of secondary shear localizations is often present within the kink bands, suggesting significant shear deformation therein. The combined observations suggest that faulting in metastable Mn₂GeO₄ olivine is a self-similar process, from grain-scale to the sample-scale. Both observed embrittlement behavior and the microstructure of metastable Mn₂GeO₄ olivine are essentially identical to those in Mg₂GeO₄ olivine we have reported previously, indicating that the physical mechanism of faulting in metastable olivine is insensitive to the specific crystallographic structure of the high-pressure phase. The low b values (about 1) observed in the faulting process in our experiments are similar to those of deep focus earthquakes in cold subduction zones. Our observed mechanism explains deep focus seismicity in cold metastable mantle wedges, provided that the self-similarity assumption holds to geological scales.

An intraoceanic Trans-Tethyan subduction zone has been identified in both the Kohistan-Ladakh arc and the West Burma Terrane. This has significant implications for the India-Eurasia collision. Concurrently, the dismembered ophiolites within the Yarlung-Tsangpo Suture Zone likely originated from the intraoceanic Trans-Tethyan subduction zone or the Andean-type southern Eurasian continental margin. A paleomagnetic study was conducted on the Lower Cretaceous (∼120–130 Ma) mafic dykes in the Xiugugabu ophiolite to resolve the uncertainty of its origin. The characteristic remanent magnetization (ChRM) obtained through stepwise thermal demagnetization successfully passed consistency/fold and reversal tests. After tilt correction, the overall mean direction of the ChRM was D = 296.9°, I = −25.5°, k = 47.6, α₉₅ = 4.5°, and N = 22, indicating a paleolatitude of 13.4°N/S and a paleopole at 15.0° N, 326.6°E with A₉₅ = 3.8°. Compared with previous paleomagnetic data from the Trans-Tethyan subduction zone, our findings strongly support the involvement of the Xiugugabu ophiolite in the intraoceanic Trans-Tethyan subduction zone. This finding reinforces the hypothesis that there were two distinct subduction zones in the Neotethyan Ocean during the Early Cretaceous. One subduction zone was situated on the southern margin of the Gangdese Arc. The second was the intraoceanic subduction zone, located approximately 3500 km from the southern margin of Eurasia, in the southern hemisphere. Our results also support a multistage India–Eurasia collision process involving continental plates, intraoceanic arcs, and terranes within the Neo-Tethyan Ocean.

This study examines subsurface deformation at the northern end of the Wadi Araba Fault (WAF), focusing on the Amman-Hallabat Fault (AHF) and the Wadi Shueib Fault (WSF). While surface evidence shows their tectonic impact from the Late Cretaceous to the present, research on their subsurface structures, contributing to the WAF, is limited. Using seismic data and well report, five seismo-stratigraphic units with significant unconformities were identified. The seismo-structural interpretation reveals a complex deformational fault zone with numerous reverse and normal faults intersecting strata from post-Precambrian rocks to the uppermost Cretaceous deposits, forming a composite flower structure with positive and negative flower characteristics. These structures show significant folding and thrusting of deposits from the uppermost Cretaceous to recent times. Seismic evidence indicates that the AHF and WSF extend upward to the Earth's surface. Fault mechanism analysis suggests a NE-SW transpressional deformation pattern, with fault formation and associated structures influenced by the Syrian Arc stress field since the Turonian. Changes in stress field orientation have significantly affected their reactivation. At its northern termination, the WAF may intersect or terminate against pre-existing faults like the AHF and WSF, influencing the WAF's behavior by accommodating strain, dissipating energy, or being reactivated as restraining bends due to the NNW-SSE-trending Dead Sea stress, leading to a complex network of distributed movement.