Validated 3D Velocity Models in Asia from Joint Regional Body- and Surface-Wave Tomography

Abstract

Abstract : We describe a method to jointly invert body-wave travel times and surface wave dispersion data for a model of compressional and shear velocities in the crust and upper mantle. The nonlinearity in the problem is handled by iterating over linearized inversion steps, with the aid of finite-difference ray tracing techniques to perform the necessary forward modeling in the updated Earth model. At each step of the iteration, we perform linearized body-wave and surface-wave inversion as separate procedures. The body-wave data, comprising first arrival P-wave times, are used to update the P velocity model. The surface-wave dispersion data are used to update the S-wave model in a two-step procedure, ignoring the small dependence of Rayleigh wave dispersion on P velocity. The separate inversions are coupled through two forms of prior information applied to their respective velocity models: constraints on the size and spatial smoothness of the velocity perturbations and bounds on the velocities themselves that are determined in part from bounds on Poisson's ratio. The new method has been applied on a 1 x 1 degree grid covering a large region of Asia, using first arriving P wave travel times from 0 to 18 degrees epicentral distance and fundamental mode Rayleigh group velocities at periods from 10 to 150 seconds. We validate the new model using standard techniques with a high quality set of travel-time observations from well located explosions and earthquakes.