Static corrections for Vibroseis data over sand dunes in western Libya

Abstract

Parts of the Murzuq Basin in western Libya are covered by linear sand dunes, which reach heights of around 100 m above the gravel plain. The sand dunes cause large increases in the travel times of reflected events in seismic data. In recent years, the conventional method used to calculate field static corrections has been to interpolate the near-surface velocity structure between upholes. Results are often unsatisfactory on lines that cross the dunes because the reflection events contain false structures that correlate with sand dune topography. These structural artefacts are caused by residual static errors which are too large for automatic statics programs to correct during processing. An alternative method of calculating field statics is to pick the first breaks on the Vibroseis field records, calculate the delay times at each station, and use the delay times directly as the field statics after applying a linear adjustment to match them to the upholes. This simple version of the refraction method does not require near-surface velocity-depth models to be produced, and gives much better results than the conventional field static method.