Laterally constrained surface wave inversion

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SUMMARYIn the last 15 yr, the use of surface waves retrieved from the cross-correlation of ambient seismic noise has significantly increased its applications to determine or monitor changes in the elastic properties of the Earth's interior. We designed a methodology for laterally constrained surface wave inversion based on a two-stage technique to estimate the 3-D distribution of the S-wave velocity (Vs). The first stage inverts traveltimes to estimate group or phase velocity dispersion maps and their inverse covariance matrix for different periods. The inverse covariance matrix is constructed explicitly using the ray tracing information. The inverse covariance matrix adds the lateral sensitivity of the maps to the structure, whereas the period-dependency provides sensitivity to the structure at depth. The second stage applies a nonlinear conjugate gradient scheme to estimate the 3-D distribution of S-wave velocity using the ensemble of velocity dispersion maps and their estimated inverse covariance matrix. We validate the methodology using a synthetic model. The results show an improved estimation of subsurface S-wave velocity structures compared to conventional point-wise inversion.