Comparison of traveltime inversions on a limestone structure

Matthew David Allen, Robert R. Stewart

Four traveltime inversion techniques were applied to two sets of seismic data collected on a Maya pyramid ruin at Maax Na, Belize. In particular, direct division, singular value decomposition, damped least squares and the conjugate gradient methods were applied. The seismic data consists of two source-receiver rings around the circumference of the pyramid with one ring near the base, and the other near the top of the pyramid. All methods produced similar velocity fields with most velocities in the range of 200-800 m/s (characteristic of carbonate rubble).

Traveltime residuals (observed minus calculated times) show an average of approximately 3ms for each method. However, based on the average and standard deviation of the residuals, the most accurate technique was found to be direct division followed by damped least-squares, singular value decomposition and lastly conjugate gradient.