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.
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：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：I propose a new analysis method for determining the intraplate stress in geodynamic models using a series of numerical simulations of mantle convection in 3D spherical-shell geometry. In the present study, the intraplate stress was evaluated from numerically obtained velocity and stress fields of mantle, and quantitatively classified into nine types by analyzing the principal deviatoric stress axes and the "stress ratio," which is a continuous parameter accounting for the stress regimes. The sensitivity of model parameters and physical conditions associated with the basic characteristics of mantle convection, such as internal heating ratio, viscosity stratification, and temperature-dependent viscosity of the mantle as well as viscoplastic rheology that causes plate-like surface motion, on the intraplate stress regimes were studied. The results demonstrated that the radial viscosity structure of the mantle interior strongly affected intraplate stress regimes, and the combination of increased viscosity in the lower mantle and the low-viscosity asthenosphere enhanced the pure strike-slip faulting regime in the stable part of plate interiors. The temporally averaged toroidal-poloidal ratio (T/P ratio) at the top surface of mantle convection with surface plate-like motion and the mantle's viscosity stratification generally ranged similar to 20-40%, which is comparable to the observed T/P ratio of present-day and past Earth. Under such Earth-like surface conditions, normal faulting regime with strike-slip component or strike-slip regime with normal faulting component, as well as pure strike-slip faulting regime, were broadly found in the stable parts of the plate interiors. From the definition of the stress regime in the present study, strike-slip faults on the real Earth are likely to occur where the strike-slip faulting component is dominant in the present models. The analysis method proposed herein is effective for evaluating the intraplate stress in research target regions, for which observation data is insufficient to determine the intraplate stress.
NSTL
Elsevier