Near-surface Seismic Investigation of Barringer (Meteor) Crater, Arizona

We investigated the shallow subsurface of Barringer (Meteor) Crater, Arizona using high-resolution seismic methods. The seismic surveys were conducted in May, 2010 during a joint expedition by the University of Houston, the University of Texas at Austin, and the Lunar and Planetary Institute (LPI). We performed compressional (P)-wave refraction analysis on the seismic data and found P-wave velocities of 450-2,500 m/s for a 55-m deep model. Away from the crater rim (toward the south), the shallow P-wave low-velocity layers thin. We also estimated a near-surface, shear (S)-wave velocity structure using a surface-wave inversion method. S-wave velocities vary from 200-700 m/s for the top 16-20 m, increasing to 900-1,000 m/s at 38-m depth. We interpret a prominent change in S-wave velocity (at around 500-600 m/s) as the transition from the ejecta blanket (a sheet of debris thrown out of the crater during the impact) to the bedrock Moenkopi sandstone. The ejecta is characterized as unconsolidated, low velocity, and low density. 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-wave and S-wave structure is interpreted as the ejecta blanket. Ultrasonic measurements on hand samples collected during the expedition give a range of P-wave velocities of 800-1,600 m/s for the Moenkopi. Predicted bulk densities from estimated S-wave velocities using modified Gardner's equation fall in the range of 1.8-2.5 gm/cm(3), with low-density materials (ejecta) underlain by high-density materials (bedrock). These density results, along with available drilling information and residual gravity anomalies, also support the thinning of the ejecta blanket.