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
  • seismic refraction
  • waveform inversion
  • Chesapeake Bay impact structure
  • impact processes
Date of Defense 2006-08-24
Availability unrestricted
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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