Fine structure of the crust inferred from linear inversion of Rayleigh-wave dispersion

Abstract

abstract The Backus-Gilbert inversion formulation applied to surface-wave dispersion measurements can be used to infer detailed shear-velocity distribution in the Earth9s crust. In this study, Rayleigh-wave group-velocity dispersion measurements were used to derive the shear-wave velocity distribution within a crustal model consisting of 15 to 20 layers whose thicknesses were held fixed. Simultaneous inversion of fundamental mode (4- to 36-sec period) and first higher-mode (3- to 8-sec period) data was sufficient to obtain crustal models displaying high resolution. In order to avoid the ambiguity associated with large side lobes in the resolving kernels, the inversion scheme was modified to yield smooth resolving kernels. This improvement was particularly important to the problem of recognition of a crustal low-velocity layer. The inversion scheme was successfully applied to both real and idealized data. It is suggested that, by using Rayleigh-wave group-velocity measurements with standard deviations of 0.03 km/sec, crustal shear-velocity models may be derived which have estimated standard deviations of 0.15 km/sec and resolving kernels with spreads of less than 7 km.