oa An Integrated Geophysical Study to Characterize the Near-Surface of Barringer Meteorite Crater

An integrated geophysical survey was conducted by University of Houston, University of Texas (Austin) and NASA in May, 2010 at Barringer (also known as Meteor) Crater, Arizona. the crater was excavated some 49,000 years ago by the impact of an iron-nickel meteorite. the crater has a diameter of 1.2 km with a rim rising some 30–60 m above the surrounding plain and 180 m deep bowl-shaped depression. the startigraphy of the area consists of Coconino sandstone overlain by the toroweap (sandstone and dolomite), followed by the Kaibab (dolomite and dolomitic limestone) and then the red Moenkopi (calcareous siltstone with iron-rich matrix and sandstone). An overturned sequence (Coconino underlain by Kaibab and then the Moenkopi above the bedrock Moenkopi) is observed at the rim and beyond as a result of the impact. the excavated debris also consists of this overturned sequence (collectively known as the ejecta blanket) and is found on the flank of the crater. the ejecta tapers as a function of distance from the crater rim. the aims of this survey were to unravel some of the existing mysteries related to the asymmetry of the crater, thickness of the ejecta blanket and its variation, depth and orientation of fractures. Different geophysical surveys (seismic, ground penetrating radar (GPR), gravity, magnetic) were conducted on the gently dipping flanks beyond the southern crater rim. A near-surface S-wave velocity structure has been obtained using the ground-roll Inversion technique. the near-surface S-wave velocity varies from 200-600 m/s within top 15 m. A change in the S-wave velocity at a depth of 10 m is observed from a seismic line at the southeast flank, which is interpreted as the transition from the ejecta blanket to the underlying Moenkopi sandstone. Ultrasonic measurements of Moenkopi hand samples indicate P-wave velocities up to 1600 m/s and Initial first-break picks show a near-surface P-wave velocity of 1700 m/s. Thus, S-wave velocities in the neighborhood of 600 m/s are reasonable. GPR surveys were also conducted at the southeast crater rim to probe the very shallow subsurface (3-5 m). Several anomalies in the GPR data were found indicating objects with a strong contrast in electrical properties with respect to the host material, possibly an iron concretion formed from the impact.