Velocity inversion from shallow VSP data using a generalized inversion technique

Abstract

A generalized inversion technique was used to determine interval shear wave velocities by inversion of vertical seismic profiling (VSP) data collected at four sites in the Mississippi Embayment. The inversion is based on an iterative process that minimizes arrival time residuals. A layer stripping method was developed to solve the forward problem and was used to compute synthetic VSP arrival times for a given velocity model. The inversion software was tested with synthetic data first and then was applied to actual VSP data. The velocities thus obtained were compared with the velocities obtained previously using a waveform matching approach (Ge et.al., 2007). In general, the inverted velocities determined using the two methods match well for three of the sites. For the fourth site the match is not good probably because the VSP data are noisy and the first arrival picks are of poor quality.