We collected high-quality teleseismic events recorded by 12 broadband seismographs deployed in the Anyuan Coal Mine and its adjacent areas in Pingxiang City, Jiangxi Province nearly two years. The H-κ-c stacking method was employed to obtain the crustal thickness, Poisson's ratio distribution, and then the crustal structure characteristics below the stations are obtained by using the time-domain linear inversion method. The crustal thickness in the Anyuan Coal Mine and its adjacent areas ranges from approximately 32 ∼ 35 km, with an average thickness of 33 km, which is consistent with the crustal thickness results in South China obtained by previous studies using receiver function method. The average Poisson's ratio of the internal medium in the study area varies between 0.22 and 0.25, which is lower than the global average of 0.27, indicating that the crustal composition is mainly composed of intermediate-acidic or felsic rocks. There is a weak negative correlation between Poisson's ratio and crustal thickness results in the Anyuan Coal Mine and its adjacent areas, suggesting that the absence of mafic-ultramafic materials in the lower crust is related with crustal delamination. The crust-mantle structure beneath the seismic stations mainly consists of three velocity discontinuity interfaces, with the first interface at a depth of approximately 1.5 km, the second one about 10∼ 15 km, and the third discontinuity being the Moho. The study also indicates that the results obtained by the H-κ-c stacking method are significantly better than those obtained by H-κ method, effectively reducing the standard deviation and dispersion of crustal thickness and VP/VS ratio.
The MASW method is robust in determine shear wave velocity of shallow site because the dispersive properties of Rayleigh wave was dominated by shear wave velocity of subsurface. Using this method, an assumption that the earth model is one dimensional and horizontal layered must be put to simplify the real earth model without considering the lateral variation. However, it is not always the truth. In order to obtain a two dimensional S-wave velocity profile of shallow site, a CMP cross-correlation (CMPCC) method was proposed by Hayashi and Suzuki (2004) to approximate two dimensional S-wave velocity profile with one dimensional inversion procedure. In order to verify its approximate resolution, a horizontal stepped layer model and a dipping layer model were chosen. The synthetic wave fields of the two models were calculated by staggered grid finite difference method. Result shows that this method can only be used to approximate horizontally stepped layer model and cannot be used to approximate dipping layer model.
Surface wave dispersion imaging approach is crucial for multi-channel analysis of surface wave (MASW). Because the resolution of inversed S-wave velocity and thickness of a layer are directly subjected to the resolution of imaged dispersion curve. The τ- p transform approach is an efficient and commonly used approach for Rayleigh wave dispersion curve imaging. However, the conventional τ- p transform approach was severely affected by waves amplitude. So, the energy peaks of f-v spectrum were mainly gathered in a narrow frequency range. In order to remedy this shortage, an improved τ- p transform approach was proposed by this paper. Comparison has been made between phase shift and improved τ- p transform approaches using both synthetic and in situ tested data. Result shows that the dispersion image transformed from proposed approach is superior to that either from conventionally τ- p transform or from phase shift approaches.
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