SH-SH wave inversion for S-wave velocity and density

SS-waves (SV-SV waves and SH-SH waves) are capable of inverting S-wave velocity (V-S) and density (rho) because they are sensitive to both parameters. SH-SH waves can be separated from multicomponent data sets more effec-tively than the SV-SV wave because the former is decoupled from the PP-wave in isotropic media. In addition, the SH-SH wave can be better modeled than the SV-SV wave in the case of strong velocity/impedance contrast because the SV-SV wave has multicritical angles, some of which can be quite small when velocity/impedance contrast is strong. We derive an approximate equation of the SH-SH wave reflection co-efficient as a function of V-S and rho in natural logarithm variables. The approximation has high accuracy, and it enables the inversion of V-S and rho in a direct manner. Both coefficients corresponding to V-S and rho are "model-parameter in-dependent" and thus there is no need for prior estimate of any model parameter in inversion. Then, we develop an SH-SH wave inversion method and demonstrate it by using synthetic data sets and a real SH-SH wave prestack data set from the west of China. We find that V-S and rho can be reliably estimated from the SH-SH wave of small angles.