Estimation of direct-arrival velocity using the linear moveout velocity analysis method with applications from eastern Saudi Arabia

Estimation of near-surface models from refraction data conventionally involves picking of arrival times for the direct and head waves. However, it is often difficult to pick the direct wave automatically on shot records if the direct-wave arrival is not a first arrival. The linear moveout velocity analysis method is proposed here to overcome this difficulty. The method is applied to help estimate the depth to the watertable at three locations in the eastern province of Saudi Arabia. The data consist of three shot records acquired in coastal sabkhas with a very shallow watertable, making it possible to check the analysis results. Conventional automatic picking algorithms failed to pick the direct arrivals in these records because the direct arrivals always come after other arrivals. The proposed method is used to estimate the direct-arrival velocities in these records and the depths to the watertable are estimated. Comparison of estimated and true water depths shows that the error was within 8%. In addition, the direct-wave velocities estimated by the proposed method showed almost perfect agreement with results from a previous study in two of the tested areas in which manual picking of the direct-wave arrivals was used.