A Method for Determination of the Three-Dimensional Seismic Velocity Structure from Local Earthquake Data.

Abstract

We have developed an inverse method to estimate a three-dimensional seismic wave velocity structure using seismic arrival time data obtained from local earthquakes. The method is characterized by a simultaneous determination of a two-dimensional depth distribution of a velocity boundary, a three-dimensional velocity distribution, station corrections and hypocenters. The depth distributions of velocity boundaries and the distributions of the slowness perturbations for P and S waves are modeled by power series of latitude, longitude, and depth, This representation of the three-dimensional seismic structure is advantageous not only in reducing the number of unknown parameters, but also in analytically evaluating the boundary depths, velocities, and partial derivatives of travel times with respect to the unknown parameters. Ray tra-jectories connected between hypocenters and stations are determined by the so-called shooting method for ray tracing scheme under a simplified velocity distribution with the exact boundary depth distribution. Numerical experiments have proved that our inverse method can successfully estimate the three-dimensional velocity structure.