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

Model of the inner crystalline crater of the Chesapeake Bay impact structure as interpreted from the seismic model. The crater is defined at the base of the Exmore tsunami breccia.
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 [Catchings et al., 2008]. Waveform inversion was applied to these data to produce a higher-resolution velocity model of the crater. Northeast of the crystalline crater, undeformed, east- ward-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 a lateral change of basement velocity occur at a radius of ~11 km, and are interpreted as the edge of the transient crater. Assuming a 22-km diameter transient crater, scaling laws predict a ~30 km diameter crater and central peak diameter of 8-10 km, consistent with the seismic image. 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.
</p><p>Catchings, R. D., D. S. Powars, G. S. Gohn, J. W. Horton Jr., M. R. Goldman, and J. A. Hole (2008), Anatomy of the Chesapeake Bay impact structure revealed by seismic imaging, Delmarva Peninsula, Virginia, USA, J. Geophys. Res., 113, B08413.
</p><p>Lester, W. R., (2006), Structure of the Chesapeake Bay Impact Crater from Wide-Angle Seismic Waveform Tomography, M.S. Thesis, Virginia Tech.
</p><p>Acknowledgements: The data were acquired by the U.S. Geological Survey funded by the National Cooperative Geologic Mapping Program and used IRIS-PASSCAL seismometers.</p>


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