Near-surface imaging of an astrobleme: Barringer (Meteor) Crater, Arizona

摘要

We acquired a suite of geophysical datasets at Barringer (Meteor) Crater in May 2010. We analyzed these datasets to build the near-surface geological model. We found P-wave velocities (from travel-time tomography) varying from 450 m/s to 2500 m/s for a 55 m deep earth model and S-wave velocities (from surface-wave inversion) of 200-1000 m/s for 38 m deep earth model. The low-velocity layers thin away from the crater and are interpreted as the thinning of the ejecta blanket (debris thrown out of the crater during the impact). Drill-hole results also show that the ejecta thickness is about 15-20 m thick near the rim and thins to 5m and less away from the rim. The gravity results also show a similar ejecta thinning trend. We measured velocities from ultrasonic experiments for different hand samples which show that P-wave velocities vary from 2700-6100 m/s and S-wave velocities vary from 1700-3300 m/s. After incorporation of a straightforward porosity effect, the ultrasonic velocities drop significantly and are comparable to the seismic, estimates. Also, deeper stratigraphic boundaries and near-surface faults have been identified from the stacked seismic section. This integrated approach shows that we have successfully imaged complex near-surface - from shallow to relatively deeper events.