Inversion of Scattered Surface Waves For Characterizing Shallow Heterogeneities

Shallow subsurface charcterization has witnessed increasing attention in the past few decades. Seismic surface wave analysis has become a standard in geo-technical engineering while applications can also be found in archeology or exploration of acquifers for example. Most current surface-wave inversion methods are aimed at recovering near-surface (shear) velocity profiles from dispersion curves, assuming horizontally layered structure. In some cases, however, one is interested in the strength or shape of local heterogeneities in the shallow subsurface. Here, we present a general inversion algorithm for scattered elastic waves, with the aim to investigate the possibility of using scattered surface waves to obtain spatially and depth resolved images of near-surface heterogeneity. We conclude that we can, in principle, recover location and strength for heterogeneities upto a depth of a Rayleigh wavelength using a few frequencies. We also compare the results to a similar but more efficient inversion scheme based on the Born approximation. We show that for shallow imaging this inversion can recover the location and actual contrast fairly well.