查看更多>>摘要：We compute a high-resolution topographic model of the Moho beneath the fault system activated during the 2016-2017 Central Italy seismic sequence, using Receiver Function (RF) analyses. We document that Ps conversions recorded in RF data-set varies abruptly at very short distance across the crustal lineament called Ancona-Anzio Line (AAL). Moho depth varies from about 25-30 km in the Tyrrhenian domain on the West to 35-40 km in the Adriatic domain in the East. Where the two domains are juxtaposed along the AAL, Moho depth values cluster around 50 km depth, in a stripe-like area 20 km wide. Such unique feature marks the deformation zone in the lithosphere and testifies the abrupt change in delamination style in the two sectors of the Apennines. Intermittent large normal faulting earthquakes driven by across-belt extension break through such inherited strong structural changes, conditioned by localized barriers to fluids migration and overpressuring.
查看更多>>摘要：It is very important to ascertain the trend of the Jiangshao Fault Zone after it enters the East China Sea for the study of the South China Block. In this paper, we intended to solve the problem based on analysis of aemmagnetic data for South China, the East China Sea, and the adjacent areas. We described the distribution and structural features of the Jiangshao Fault Zone, and identified magnetic anomaly features, fault structures, and volcanic rock suites, along with the spatial distribution of igneous bodies with a high magnetic susceptibility. The spatial extent of the Jiangshao Fault Zone onland and offshore was determined through a comparison of the magnetic anomaly features with the geology and inferred structures. The Jiangshao Fault Zone extends from onland to offshore along a NE-SW trend. The formation of the Jiangshao Fault Zone was determined by comparing the stratigraphy and structures of the basement rocks, lithological units, and geological histories of the Yangtze and Cathaysia blocks. The spatial distribution of magmatic bodies with high magnetic susceptibility in the South China Block was revealed by the inversion results of aeromagnetic data. These findings contribute to understanding the tectonic evolution of the Yangtze and Cathaysia blocks, and provide insights into the geological structure of the East China Sea and formation of the East China Sea Shelf Basin.
查看更多>>摘要：A similar to 400 m thick Middle-Late Triassic volcano-sedimentary succession crops out in a relatively narrow corridor similar to 5 km long and similar to 25 km wide close to Antalya Gulf, SW Turkey. The volcanic and subvolcanic rocks represent the majority of the succession and are associated with epiclastic breccia, turbiditic sediments as well as chert and limestone layers. The igneous rocks are alkali basalts, with incompatible element content matching the classical HiMU-OIB types. These are considered as the precursors of a rift system that would have later evolved into a mature Neotethyan oceanic system, with emplacement of massive tholeiitic basalt sequences, not recorded in the investigated area. Clinopyroxene-melt thermobarometric constraints indicate the presence of two main magma chambers, one equilibrated at similar to 7-10 km depth and similar to 1070 degrees C and the other at similar to 15-21 km depth and similar to 1300 degrees C. Based on these estimates, a 3-D finite element modelling has been applied, simulating the presence of ellipsoidal magma chambers at different depths and with variable sizes, applying different boundary loading conditions. The scenario that best fits the distribution of the volcanic rocks assumes the contemporaneous presence of two magma reservoirs. One is shallow, with a size of similar to 17 x 1.5 x 1.5 km, and the second is deeper, with a size of similar to 37 x 3 x 3 km. Numerical simulations show maximum 6 m opening and dilation through horizontal plane at the surface during the Permian/Triassic intracontinental rift phases. Morphological constraints of this rift zone, with the presence of massive lava eruptions also as pillow facies, have been simulated with the existence of a slowly opening rift system. In order to produce the voluminous magma batches in the Antalya region, pure extensional tectonic regimes seem insufficient, and the presence of a transtensional regime must have accompanied the tectonic forces during the Triassic intracontinental rifting stage.
查看更多>>摘要：We present new crustal models of azimuthally anisotropic P-wave velocity, isotropic P-wave velocity (Vp), isotropic S-wave velocity (Vs) and Vp/Vs ratio for the Salton Trough. High Vp/Vs ratio is revealed at depths of 2-8 km along the San Andreas Fault, implying the possible presence of fluids. High Vp and high Vp/Vs ratio (>1.8) structures of the mid-lower crust beneath the Salton Trough possibly reflect the underplated gabbroic rocks as a result of the extension-induced partial melting of the upwelling asthenospheric materials. The fast velocity directions (FVDs) generally correlate with the direction of the maximum horizontal compressive stress except that fault-parallel FVDs are found at main fault traces. However, the FVDs in the Salton Trough show complex features. The northern Slaton Trough basin (the northern Salton Sea basin and Coachella Valley basin) is dominated by NW-SE FVDs, which are possibly due to the active compression happening there. E-W oriented FVDs predominate the upper crust of the southern Salton Trough basin (the southern Salton Sea basin and Imperial Valley basin), possibly due to faulting and/or block rotation. As the depth increases (12-18 km), the FVDs to the south of the Salton Sea have an overall rotation and gradually become NW-SE. The depth-dependent variation of anisotropy orientation may be attributed to a large band of underlying heat source that probably causes a change of stress field by imposing thermal stress on overlying rocks. In all, our velocity models suggest that faults in the Salton Trough may bear a high risk of mechanical failures due to the complexities of stress distribution and geological structures as well as the presence of a large volume of fluids and heat.
查看更多>>摘要：Syntectonic sediments record the growth process of active fold and fault belts. The Quaternary in the Chengdu plain are the syntectonic sediments formed during the structure deformation of the Longmen Shan in Late Cenozoic, which is of great significance for understanding the formation and evolution of the Longmen Shan. However, the geometry and formation of the Quaternary in the Chengdu plain are still unsettled. This paper determines the Quaternary thickness in the Chengdu plain with audio magnetotellurics (AMT), electrical resistivity tomography (ERT) and borehole, and discusses the formation of Quaternary in the Chengdu plain in combination with previous deep and surface data. It also predicts the Quaternary geometry in Chengdu plain by AMT, and concludes that the thickness in Huayuan may be larger than that in Zhuwapu (541 m). The borehole reveals that the Quaternary thickness in the Huayuan is upto 571.3 m, which is the thickest Quaternary so far. With the Longmen Shan piedmont wedging into the Sichuan basin, and under the intense erosion of Minjiang river, structure wedges of different scales are formed and result in salient and recess, which corresponds to the geometry of the Quaternary in the Chengdu plain. Therefore, the coupling between deep structures and surface processes controls the formation of the Quaternary in the Chengdu plain.
查看更多>>摘要：How deep the two opposite dipping subduction zones in the vicinity of Taiwan, northwestward-dipping Philippine Sea Plate (PSP) and eastward-dipping South China Sea Slab (SCS), penetrated down into mantle, are hotly on debate and insufficiently imaged by seismic tomographic inversions, either due to inadequate quantities of seismic data or limited vertical resolution of the techniques used by previous investigations. Here we employ an unprecedented number of 55,847 high-quality P-to-S radial receiver functions recorded by 304 broadband seismic stations located in SE China and adjacent areas to image the topography of the mantle transition zone (MTZ) discontinuities (d410 and d660) to delineate the configurations of the subducted slab segments and analyze the impacts of thermal and water content anomalies on the MTZ. The close-to-normal wavespeed-corrected d410 and a similar to 10 km depression of the corrected d660 to the east of northern Taiwan are revealed, indicating that the PSP breaks off above the d410 and the delaminated PSP drops into the lower MTZ along with slab dehydration. To the east of southern Taiwan, where the SCS begins to subduct eastward, the uplift of the apparent d410 is nearly twice as much as that of the d660. The positive wavespeed anomaly above the d410 and low temperature in the vicinity of the d410 are enough to contribute to the uplift of MTZ discontinuities, suggesting that the SCS just reaches the d410, rather than penetrating the entire MTZ.
查看更多>>摘要：Decoupled hydro-shearing has been a classic mechanism of fluid-induced seismicity for decades. An alternative is coupled hydro-mechanical triggering, largely based on the theory of linear poroelasticity. Unfortunately, fractures and their alterations to a canonical poroelastic system are rarely accounted for, and seismicity is typically forecasted as event rate without producing catalogs. Here, I present a new approach to modeling fluid-induced seismicity in arbitrarily fractured poroelastic media. The hydro-mechanical triggering is modeled using a computational model that resolves fluid storage and nonlinear flow within fractures and full poroelastic coupling within the matrix. Seismological modeling is achieved stochastically by generating stress drops based on the full inter-seismic poroelastic stressing history. The two steps are sequentially coupled and advanced in time via a prediction-correction scheme, allowing for fracture stress updating and synthetic event catalog assembly. To demonstrate model capabilities and effects of fractures and full coupling on overpressure, stress, and seismicity, I perform three microseismic-scale numerical experiments by adding fractures and poroelastic coupling into a diffusion-only base model, and model previously unknown mechanisms. In contrast to existing models, this model produces both repeating and linear clustering of seismicity. Poroelastic coupling enhances the clustering, increasingly inhibits near-field seismicity and favors remote seismicity over time, and significantly reduces the overall event population. Meanwhile, statistical characteristics including the Gutenberg-Richter scaling relation persist, and the b-value elevation for microseismicity is attributable to a mechanical origin.
查看更多>>摘要：A lithospheric density structure of the Bay of Bengal (BoB), which includes the thickest sedimentary layers deposited after continental rifting, is determined from constrained 3D/2D gravity modeling, to understand intricate tectonics processes of the region. The results suggest lateral density variation in the sub-crustal lithospheric mantle and high-density upper mantle is found beneath the thick sedimentary region of BoB. The present density model also predicts the thick lithosphere beneath the huge pile of sediments. The dense and thick lithospheric mantle results are supported by global tomographic and other geophysical results. It is also noticed that the dense mantle and thick sedimentary region have high elastic strength. We propose that the density and strength of the lithospheric mantle in the northern BoB are increased with age and sedimentation since rifting. The cause of density changes in the mantle is indistinct and could occur due to numerous reasons such as the transformation of mantle material catalyzed by a change in pressure and temperature conditions, or mantle flow.
查看更多>>摘要：The location of the Continent-ocean boundary (COB) between the Palawan continent block (PCB) and the central oceanic basin remains controversial. There are more than 100 km difference among the scholars' view about the specific positions of the COB. To obtain a more reasonable location of the COB in the PCB, a comprehensive interpretation was conducted based on new shipborne geophysical data, including bathymetry, gravity, magnetic and reflection seismic data. In particular, upward continuation was applied to the new stern-towing magnetic data, and analytical signal analysis (ASA) processing was adopted for the total field magnetic anomalies, including both the public and stern-towing magnetic data. The most reasonable COB of PCB is just identified with the geophysical data based on the comprehensive structures' anomalies, such as the foot of massif slope and the magmatic volcanoes in topographic data, and the gentle gradient of the free-air and Bouguer gravity anomalies, and the clear dividing boundary in magnetic ASA sharp anomaly, and the seismic profiles structure's display in the Continent-ocean transition (COT). Meanwhile, structural modeling along the seismic profiles are used to constrained the identification. The refined convex-coneave's COB is distributed at the seaward limit of the continental crust along the foot of northwest Palawan slope with a hyper-extended thinner crust, seaward-dipping listric faults, and is reasonably located between the extensive thinned continental crust and expansive subducting oceanic crust.
Quang-Minh NguyenHsu, Shu-KunLin, Andrew Tien-ShunYang, Chih-Cheng...
11页
查看更多>>摘要：The offshore area of northern Taiwan is currently in an extensional regime, known for a post-collision area of the Taiwan mountain belt that has formed due to the oblique collision of the Philippine Sea Plate against the Eurasian continental margin since the late Miocene. The active collision has undergone a progressive migration of the Taiwan mountain belt from the northeast to the southwest direction. After the relaxation of the compressional stress due to the westward subduction of the Philippine Sea Plate, the northern Taiwan orogen has collapsed together with the opening of the southern Okinawa Trough. Here, we show the transitional process from compressional to extensional regime in the area off northern Taiwan and reconstruct the tectono-sedimentary evolution by using multi-channel reflection seismic data. We process and interpret multi-channel seismic profiles and use borehole data to determine the ages of sedimentary units and stratal surfaces/unconformities. Based on the seismic facies, we have recognized two distinctive domains separated by the Offshore Shanjiao Fault (OSF): a shelf basin to the northwest and a collapsed zone to the southeast. The tectonosedimentary evolution off northern Taiwan since the late Miocene can be described in 4 stages. (1) The compressional structures off northern Taiwan were formed during the collision period starting around 6 Ma, a series of folds-and-thrusts aligned in the NE-SW direction. (2) Due to the oblique collision, some NW-SE-trending strike-slip faults were developed across the collision belt to accommodate the differential displacements between two adjacent segments of the folded belt. (3) During the transition from compressional to extensional regime at about 2.7 Ma, a post-collisional erosion and subsidence occurred in the collapsed zone to form the basal unconformity. This post-collisional collapse is associated with the opening of the southern Okinawa Trough, a back-arc basin, due to the westward migration of the Philippine Sea Plate subduction beneath the southern Ryukyu arc. (4) The offshore area of northern Taiwan has subsided continuously with sediment accumulation since the early Pleistocene (similar to 2.0 Ma), accompanying the rifting of the southern Okinawa Trough.
NSTL
Elsevier