Structure of the Chesapeake Bay Impact Crater from Wide-Angle Seismic Waveform Tomography

Details Structure of the Chesapeake Bay Impact Crater from Wide-Angle Seismic Waveform Tomography Structure of the Chesapeake Bay Impact Crater from Wide-Angle Seismic Waveform Tomography

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.s43d..04l&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #S43D-04

Statistics

Computation

0902 Computational Methods: Seismic, 7270 Tomography (6982, 8180), 8136 Impact Phenomena (5420, 6022)

Scientific paper

The 35 million year old Chesapeake Bay impact structure is one of the largest and most well preserved meteor/comet impact structures on Earth. As a marine impact on a continental shelf, its morphology consists of a deep inner crater penetrating pre-existing crystalline basement surrounded by a much wider, shallower crater within the overlying sediments. In 2004, the U.S. Geological Survey conducted a combined refraction and low-fold reflection seismic survey across the northern part of the inner crater with the goals of constraining crater structure and identifying an ideal drill site for a deep borehole. Waveform inversion was applied to the seismic data to produce a high-resolution seismic velocity model of the inner crater. This significantly improved the spatial resolution over previous images based on travel times. Under the northeastern part of the outer crater, eastward-sloping, relatively intact crystalline basement is at a depth of ~1.5 km. The edge of the inner crater is at ~17 km radius and slopes gradually inward to penetrate pre-existing crystalline basement. The top of crystalline rock on the central uplift is about 0.8 km higher than its surroundings. Seismic velocity of crystalline rocks under the inner crater is much lower than under the outer crater, suggesting strong fracturing/brecciation of the inner crater floor and even stronger brecciation of the central uplift. A basement uplift and lateral change of basement velocity occurs at a radius of ~12 km and is interpreted as possibly indicating the edge of the transient crater caused by impact excavation prior to collapse. Assuming a 24 km diameter transient crater, scaling laws based on extraterrestrial craters and numerical models predict the observed inner crater diameter, central uplift diameter, and inner crater depth. This suggests that the crater collapse processes that created the inner crater in crystalline rocks were unaffected by the much weaker rheology of the overlying sediments.

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