Picking and fitting of first-break times measured on Gabor transforms of uncorrelated Vibroseis VSP signals

Joe Wong

Estimates of the bulk dispersive velocities of an earth volume can be obtained from the Gabor transforms of uncorrelated Vibroseis signals recorded in VSP surveys. The transforms provide time-frequency displays on which first-break times can be picked automatically using a modified energy attribute. Analysis of these times gives directly measured estimates of the frequency-dependent velocity of the bulk rock volume through which the seismic waves have propagated. Due to low signal-to-noise ratios that occur in real field data, the picked times will usually have outliers and random variation across the frequency axis. After eliminating the outliers, least-squares nonlinear regression based on a relatively simple fitting function smoothly fits and interpolates the picked times.