Near-surface geophysical imaging of Barringer (Meteor) Crater, Arizona

Abstract

We investigated the shallow subsurface at Barringer (Meteor) Crater, Arizona using seismic and gravity techniques. We found compressional (P)-wave velocities of 450-2500 m/s for a 55 m deep section from seismic refraction analysis. The low uppermost P-wave velocity layers thin away from the crater rim (toward the south). Shear (S)-wave velocities (estimated from ground-roll inversion) vary from 200-700 m/s for the top 16-20 m increasing to 900-1000 m/s at 38 m depth. The prominent change in S-wave velocities (around 500-600 m/s up to 20 m depth) is interpreted as the transition from the low-velocity ejecta blanket (a sheet of debris thrown out of the crater during the impact) to the bed-rock Moenkopi sandstone. This S-wave transition takes place at a depth range of 12-20 m near the crater rim with a thinning away from the crater rim. This consistent P- and S-wave layer is interpreted as the ejecta blanket. Near-surface reflection seismic analysis provided relatively deeper information indicating at least four sub-horizontal reflectors intersected by a number of faults. Staking velocity analysis estimates P-wave velocities up to 3500 m/s (for the top 500 ms) showing a similar P-wave thinning structure (especially for top 200 ms). Ultrasonic measurements on hand samples provide a range of P-wave velocities of 800-1600 m/s for the Moenkopi consistent with seismic refraction results. The estimated residual gravity profile also supports the identified thinning of the ejecta blanket in seismic analysis.