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

Seismic velocity model produced by waveform inversion of 3-16 Hz data.
<p>
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>References
</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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