Dynamic time corrections and their application to seismic data over sea floor canyons in the Gippsland Basin

Abstract

Seismic reflection events beneath marked lateral velocity variations are distorted by complex ray paths. This can result in a stacked section with events that show poor continuity and are affected by 'pull up' or 'push down'. Where the velocity anomaly is not near the surface, conventional statics often fail to produce an adequate result.A pre-stack solution based on ray tracing is presented, which applies dynamic time corrections that vary with offset and travel time. The method was applied to a grid of data in the Gippsland Basin, affected by deep erosional canyons on the sea floor. The resulting sections generally showed significant improvement to the continuity of events thus enabling depth maps of greater accuracy to be constructed. We conclude that the method is more suitable in the study area than other pre-stack techniques given the absence of steep dips beneath the canyons and the exploration objectives. Other applications of the method are also mentioned.