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

Abstract

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 bed-rock 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/cm3, 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.