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.
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：The fact that the same fault may host different rupture or slip modes was partly attributed to the change in strain rate of the fault in previous studies. However, contradictory observations were obtained in the previous experimental studies, that is, the loading rate can promote or inhibit the rapid instability of faults. Although the two opposite effects of the loading rate were separately explained in the previous studies, the contradiction remains unresolved. Based on an experiment conducted on a granodiorite sample, we use the cumulative fault slip to quantitatively describe the slip-driven changes in fault properties and study the cross-effects of loading rate and cumulative fault slip on the pre-seismic rupture speed, unstable slip rate, and friction coefficient drop of the laboratory earthquakes (stick-slip events). The experimental results show that under the same loading rate, the exponential propagating rupture speed, the unstable slip rate, and the friction coefficient drop of the stick-slip events increase with increasing cumulative fault slip. As a result, the loading rate has opposite effects on the exponential propagating rupture speed, the unstable slip rate, and the friction coefficient drop under different amounts of the cumulative fault slip. This provides an explanation for the observation contradiction that the loading rate can promote or inhibit the rapid instability of the fault. The experimental results also reveal that the steady rupture speed is approximately proportional to the loading rate but weakly depends on the cumulative fault slip. Finally, the significance of the experimental results for understanding the earthquake and faulting mechanics is discussed.
Taymaz, TuncayYolsal-Cevikbilen, SedaIrmak, T. SerkanVera, Felipe...
24页
查看更多>>摘要：We resolve source mechanism and rupture process for the Neon Karlovasion, Samos Mw 7.0 earthquake that struck Greek-Turkish border regions on 30th October 2020 acquired from kinematic joint inversion of teleseismic body-waves and near-field strong ground-motion waveforms. The optimal kinematic finite-fault slip model indicates a planar E-W striking north-dipping normal faulting mechanism with strike phi = 270 degrees +/- 5 degrees, dip delta = 35 degrees +/- 5 degrees, rake lambda = -94 degrees +/- 5 degrees; centroid depth h = 11 +/- 2 km; duration of the source time function STF = 26 s and seismic moment M-0 = 3.34 x 10(19) Nm equivalent to Mw = 7.0. Our final finite- fault slip models exhibit two main asperities within a depth range from similar to 20 km to the surface. The dynamic rupture model exposes an initial heterogeneous stress distribution with variations up to 25 MPa. The near-field strong motion waveforms constrained the slip model suggesting up-dip and westward propagation of the bilateral rupture pattern with a maximum slip of 3.2 m, illuminated by back-projection (BP) analysis. The high-frequency (HF) back-projected rupture showed a predominantly E-W striking component (similar to 75%) with directivity of 277 degrees that propagates to the surface along a 60 km long and 24 km wide fault plane in 20 s at a slower speed range of 1.0-2.0 km/s. This well constrains the coseismic slip region where the aftershock sequence confirms distributed deformation. Our back-projection analyses elucidates a dominant HF rupture stage (0-13 s) tracked first on the epicentre area and further along the downdip in the region of maximum coseismic slip indicating similar to 15 km of persistent rupture. The latter HF emissions (13-20 s) remark a speed of about 3.0 km/s and a westward extension of the rupture up to 30 km from the preceding rupture segment to shorelines at the northeast of the Ikaria Island.
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：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：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：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：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.
NSTL
Elsevier