Application of SPAC method to estimate the crustal S-wave velocity structure

Abstract

S-wave velocity structure can reflect the differences of physical properties of Earth media, and is the important basis of identifying the structural characteristics of the low velocity zone. This article attempts to use spatial autocorrelation method (SPAC method) to extract Rayleigh-wave phase velocity dispersion curves from the vertical component of the seismic stations' microtremors, and through the inversion of dispersion curve, acquires the S-wave velocity structure. Taking 8 broadband seismic stations' actual measurement from China National Seismic Network for example, we acquired the one-dimensional S-wave velocity structure of 30 km depth range using this method in the Capital area near Beijing. The inversion result shows that the crystalline basement of this region is about 2 km deep; there is S wave low-velocity layer at 5 similar to 8 km and 12 similar to 16 km depth; the depth 8 km and 20 km stands for the speed interface of S-wave that has a big speed difference. This result has good consistency with seismology and artificial seismic exploration results, which illustrates that estimating the crustal S-wave velocity structure using spatial autocorrelation method is feasible and effective.