Sensitivities of surface wave velocities to the medium parameters in a radially anisotropic spherical Earth and inversion strategies

Sankar N. Bhattacharya

Abstract


Sensitivity kernels or partial derivatives of phase velocity (c) and group velocity (U) with respect to medium parameters are useful to interpret a given set of observed surface wave velocity data. In addition to phase velocities, group velocities are also being observed to find the radial anisotropy of the crust and mantle. However, sensitivities of group velocity for a radially anisotropic Earth have rarely been studied. Here we show sensitivities of group velocity along with those of phase velocity to the medium parameters VSV, VSH , VPV, VPH , h and density in a radially anisotropic spherical Earth. The peak sensitivities for U are generally twice of those for c; thus U is more efficient than c to explore anisotropic nature of the medium. Love waves mainly depends on VSH while Rayleigh waves is nearly independent of VSH . The sensitivities show that there are trade-offs among these parameters during inversion and there is a need to reduce the number of parameters to be evaluated independently. It is suggested to use a nonlinear inversion jointly for Rayleigh and Love waves; in such a nonlinear inversion best solutions are obtained among the model parameters within prescribed limits for each parameter. We first choose VSH, VSV and VPH within their corresponding limits; VPV and h can be evaluated from empirical relations among the parameters. The density has small effect on surface wave velocities and it can be considered from other studies or from empirical relation of density to average P-wave velocity.


Keywords


Crust-mantle structure; Radial anisotropy; Surface waves

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References


DOI: https://doi.org/10.4401/ag-6806
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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X