Title page for ETD etd-09172006-145835


Type of Document Master's Thesis
Author Lester, W. Ryan
Author's Email Address wlester@vt.edu
URN etd-09172006-145835
Title Structure of the Chesapeake Bay Impact Crater from Wide-Angle Seismic Waveform Tomography
Degree Master of Science
Department Geosciences
Advisory Committee
Advisor Name Title
Hole, John A. Committee Chair
Burbey, Thomas J. Committee Member
Imhof, Matthias G. Committee Member
Keywords
  • seismic refraction
  • waveform inversion
  • Chesapeake Bay impact structure
  • impact processes
Date of Defense 2006-08-24
Availability unrestricted
Abstract
The Chesapeake Bay impact structure is one of the largest and most well preserved impact structures on Earth. It has a unique morphology composed of an inner crater penetrating crystalline basement surrounded by a wider crater in the overlying sediments. In 2004, the U.S. Geological Survey conducted a seismic survey with the goals of constraining crater structure and in support of the drilling of a borehole into the deepest part of the crater. Travel-time and waveform inversion were applied to the data to produce a high-resolution velocity model of the crater. Low-fold reflection processing was also applied. Northeast of the crystalline crater, undeformed, eastward-sloping crystalline basement is ~1.5 km deep. The edge of the inner crater is at ~ 15 km radius and slopes gradually down to a depth of 1.5 - 1.8 km. A central peak of 4-5 km radius rises to a depth of ~0.8 km. Basement velocity in the crystalline crater is much lower than undeformed basement, which suggests ~10% fracturing of the crater floor, and up to 20% fracturing of the central uplift. A basement uplift and lateral change of velocity, interpreted as the edge of the transient crater, occurs at a radius of ~ 11 km. Assuming a 22 km diameter transient crater, scaling laws predict a ~30 km diameter crater and central peak diameter of 8-10 km. This indicates that post-impact collapse processes that created the ~ 30 km diameter crystalline crater were unaffected by the much weaker rheology of the overlying sediments.
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