SEISMIC CHARACTERIZATION OF NEAR-SURFACE ANISOTROPIC STRUCTURE

In many geophysical applications, the neglect of anisotropy is somehow an oversimplification. The mismatch between the theory and the observation of near-surface seismics indicates the need for the inclusion of medium anisotropy. In this paper, surface wave (Love wave) dispersion properties are used to estimate the anisotropic structure of the near-surface layered earth, which is modeled as vertical transverse isotropy (VTI), a reasonable assumption for the vertically symmetric anisotropic medium. First, the dispersion curves, which are the numerical solutions of the dispersion equation, are obtained by a graphic-based method. Compared with traditional root-finding algorithms, this graphic-based method is simpler, faster, and more precise. Then, very fast simulated annealing (VFSA) algorithm is used to invert velocity structure and anisotropy structure simultaneously. The advantages of VFSA are two-fold: 1) high capability to find global minimum, and 2) independence to the initial model. The proposed algorithm is verified by the synthetic dispersion curve generated by a VTI medium model. Finally, the estimation of shear wave velocity and anisotropy structure of the field data at a site of sediments in the Connecticut River Valley shows this approach’s feasibility and efficiency.