Mapping the velocity and radial anisotropy of the sediment basin using modified cross-correlation beamforming of the multimode ambient noise at a dense linear array: application in Fuyang, Sourthern China

Summary The Fuyang Depression, located in the Southern North China Basin, exhibits promising gas generation potential and favorable hydrocarbon accumulation conditions. The hydrocarbon resource survey in this region has primarily involved active-source seismic exploration and drilling operations. Dense-array ambient noise imaging has proven to be an efficient and low-cost detection technique, providing background information on the reservoir accumulation conditions in sedimentary basins. This study utilizes continuous ambient noise records from two linear dense arrays in the Fuyang depression to build S-wave velocity structures and radial anisotropy models down to 3 km beneath the arrays. A modified cross-correlation beamforming method is applied to sub-arrays of the linear array to extract dispersion curves of the fundamental mode and first overtone Rayleigh waves, as well as fundamental mode Love waves, from the ambient noise. The phase-velocity cross sections of different surface wave modes beneath two linear arrays are thereby obtained directly without tomographic inversion. Depth inversion is then performed to derive SV- and SH-wave velocity structures and radial anisotropy for the two linear arrays. The sediment thickness of Quaternary and Neogene (Q+N) sedimentary sequences are delineated by the iso-velocity of S-wave at 1.3 km/s, calibrated with the borehole data. The widespread negative radial anisotropy layers are observed at the shallow subsurface, which are interpreted as the water-saturated open fractures. The S-wave velocity and radial anisotropy models provide valuable constraints for both seismic hazard assessment and hydrocarbon exploration within sedimentary basins.