Teleseismic Virtual-Source Imaging of the Basin Structures in the Three Gorges Region, China

摘要

The teleseismic virtual-source reflection (TVR) profiling method uses free-surface reverberations of the teleseismic P-wave (PPdp phase) data to produce an image of the subsurface. Upper-crustal reflections can be retrieved by deconvolving the average source wavelet for all stations in an array from the teleseismic P-wave coda recorded at each station of the array. We present a case study for which we construct the upper-crustal TVR images in the Three Gorges (TG) region, China, based on a dataset of four teleseismic events recorded by a linear regional array of geophones. The features in the resultant TVR images, such as the geometry of the Zigui and Sichuan basins, correlate well with the surface geologic observations at the TG region. We identified reflectors in the Zigui and Sichuan basins that indicated their maximum depths at 2.6 and 7 km, respectively. The basin structure is consistent with the compressional stress regime that is evident by two reverse faults in the region: the Gaoqiao fault, corresponding to a basement ridge in the TVR image that separates the two basins, and the Xiannvshan fault.