Zhang, YayunYao, HuajianXu, MinLiu, Bin...
11页查看更多>>摘要：The Fujian-Taiwan Strait-Taiwan area has undergone multiple periods of alternate compressional and extensional tectonic events, forming a complex geological structure. The underground structure and deformation characteristics, reflected by three-dimensional velocity structure and anisotropy, are the basis for analyzing the influences of different geological processes. In this study, utilizing 2 years of continuous waveform data from more than 100 permanent stations in Fujian and Taiwan, we extracted Rayleigh and Love wave dispersion data based on the cross-correlation of vertical and tangential components. A direct inversion method was employed to obtain the 3-D shear wave velocity and radial anisotropy structure of the crust. Vertical and horizontal polarized shear wave velocity structures were also inverted separately, and then used to calculate another radially anisotropic velocity model for comparison. The results show that the middle and lower crust of Fujian and the Taiwan Strait are dominated by positive radial anisotropy attributed to the near-horizontal alignment of minerals caused by extension. Although in an extension environment, most of the shallow crust exhibits weak anisotropy due to the vertical cutting of fractures and fissures, except for the strait area covered by horizontal sedimentary layers leading to strong positive radial anisotropy. In addition to the influence of faults and other shallow structures, the stress distribution caused by metamorphism also plays an important role; thus, the upper crust of the marine metamorphic belt shows negative radial anisotropy. Different from the strong positive anisotropy in other parts of the lower crust, relatively weak anisotropy appears beneath the Penghu area, which is related to two-stage Cenozoic extension.
原文链接:
NSTL
Elsevier
She, YuyangYao, HuajianYang, HongfengWang, Juanjuan...
9页查看更多>>摘要：The depth extent of low velocity fault zones is still a matter of debate due to the lack of vertical resolution for most seismic methods. Autocorrelations and cross-correlations of seismic ambient noise provide us new constraints on this issue by obtaining the shallow subsurface reflections without the need of active sources or earthquakes. The horizontal-to-vertical spectral ratio (HVSR) method can also give constraints on this interface and does not need any extra cost of data collection. In this study, we used one-month continuous seismic data from a dense linear array deployed crossing the Chenghai Fault (CHF) in Yunnan, southwest China. Single station autocorrelation and adjacent station pair cross-correlation methods were used to retrieve body wave reflections from the interface of the shallow crustal low-velocity zone (LVZ). The HVSR method was also performed to delineate the shape of the LVZ. Results show an inverted trapezoidal LVZ which extends to similar to 1.0 km depth across the fault zone with a lateral extent of similar to 3 km. Previous studies based on ambient noise surface-wave tomography and teleseismic travel time analysis in the same area show similar characteristics, consistent with the interpretation of our results.
原文链接:- NSTL
- Elsevier
Stein, ClaudiaComeau, Matthew J.Becken, MichaelHansen, Ulrich...
17页查看更多>>摘要：Delamination of the lower crust or lithospheric mantle is one explanation for the surface uplift observed in areas of mountain building. This process describes the removal of the lower part of the tectonic plate and can occur in various ways. Different styles of delamination typically have in common that the upper material (e.g., lowermost crust or lithospheric mantle) is denser than the underlying material (e.g., asthenosphere) and therefore sinks. It has been proposed that the higher density can be caused by the formation of eclogite. In this study we apply a thermomechanical model featuring a density increase within the lithosphere by a phase transition. The model setup is designed to investigate surface uplift and mountain building in an intracontinental setting. Specifically, the model is arranged to closely resemble central Mongolia. The models give insights into the dynamically evolving flow field with respect to the style of removal, therefore the general outcome is also applicable to other orogenic regions. In addition to a systematic study on the phase transition, we also investigate the influence of convergent motion and of the rheology of the crust. Our results reveal that for the absence of a dense (eclogite) layer, delamination initially occurs as a stationary Rayleigh-Taylor instability which appears as a late and short-lived event. In comparison, for a strong density contrast an early, long-lived peeling-off removal style with a stationary slab results. The subsequent asthenospheric upwelling causes further peeling-off events for all density contrasts. For this removal style a retreating slab is observed that occasionally breaks off giving way to a periodic behaviour. The findings confirm that a strong convergence and low viscosity of the crust promote delamination. In addition, the asthenospheric upwelling yields a wide and flat surface uplift. Such dome-like features are observed to be more pronounced for high density contrasts (i.e., strong eclogitisation).
原文链接:- NSTL
- Elsevier
