Analysis of velocity structure and radial anisotropy of sediments in Xiong′an New Area using modified cross-correlation beamforming method

The high-resolution 3D S-wave velocity structure of sedimentary basins is an important parameter that needs to be understood for seismic risk assessment and prevention of large earthquakes. The ambient noise array technique based on dense array is an effective method for constructing S-wave velocity in sedimentary basins. However, the incompatibility of Rayleigh and Love wave dispersion curves extracted from the ambient noise suggests a radial anisotropy in the sedimentary basins. In this paper, a high-resolution 3D S-wave velocity model and radial anisotropy model of the Xiong′an New Area sedimentary basin is constructed based on the dense array composed of 894 stations. Firstly, the whole array is divided into 864 subarrays with grid size of 0.1°× 0.1°. For each subarray, the fundamental and first overtone Rayleigh wave dispersion curves, and the fundamental Love wave dispersion curve are extracted from the noise cross-correlation function of the vertical-vertical (ZZ) component and the transverse-transverse (TT) component using the new imaging conditions of the modified cross-correlation beamforming (MCBF) method. The lateral distributions of the phase velocities of Rayleigh and Love waves at different periods are then obtained without tomography. The Rayleigh and Love wave dispersion curves of each sub-array are then inverted for the SV and SH wave velocity by depth inversion. The 3D Voigt average S-wave velocity structure and radial anisotropy at a depth range of 0 ~ 2 km are constructed using the SV and SH profile of each sub-array. The results show that the MCBF can effectively extract the multi-mode surface wave dispersion curves from the ambient noise. The crossed artifacts can be removed from the dispersion image using the new imaging condition of MCBF. The 3D S-wave velocity structure in the Xiong′an New Area is consistent with the geologic structure and the distribution of radial anisotropy within sedimentary basin can provide valuable insights for the exploration of geothermal resources.