Seismic tomography of a Maya pyramid: Chan Chich, Belize

Chuandong (Richard) Xu, Robert R. Stewart

A seismic survey was conducted on a Mayan pyramid ruin at Chan Chich, Belize, Central America in June, 2000. The purpose of this survey was to test whether a hammer seismic technique could propagate energy through the carbonate-rubble and mortar pyramid (30 m x 30 m at the base), and if this energy could be used to make images of the interior of the structure. To this end, ten 3-component geophones were planted, with 2 m spacing, on one side of the pyramid. Source points were acquired around the corner on an adjacent side of the pyramid at a 4 m spacing - giving a geometry like that of a VSP on its side. The sledge-hammer source was struck about 20 times per shot point. We analyze the VSP-type dataset here by picking first-break arrivals from 60 seismic traces and performing a traveltime inversion to estimate the velocities inside the pyramid. Finally, a velocity contour map is given with resolution and reliability analysis. We find that the near-surface of the pyramid has velocities about 100~200 m/s while the interior has higher velocities (500 m/s to 700 m/s). There is evidence of a low velocity region amongst the higher velocity areas.