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Bulletin of the Seismological Society of America; June 2003; v. 93; no. 3; p. 998-1011; DOI: 10.1785/0120020062
© 2003 Seismological Society of America
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Ground-Motion Attenuation in the Atlantic Coastal Plain near Charleston, South Carolina

Martin C. Chapman, Pradeep Talwani and Richard C. Cannon

Department of Geological Sciences
4044 Derring Hall
Virginia Polytechnic Institute and State University
Blacksburg, Virginia 24061
mcc{at}vt.edu
(M.C.C.)

Department of Geological Sciences
University of South Carolina
701 Sumter St.
Columbia, South Carolina 29208
talwani{at}geol.seis.sc.edu, cannon{at}geol.seis.sc.edu
(P.T., R.C.C.)

Charleston, South Carolina, lies on approximately 1 km of Cretaceous and Cenozoic sediments of the Atlantic Coastal Plain. Estimation of high-frequency absorption due to these sediments is important for strong motion prediction. We attempt the measurement using microearthquake data recorded at small distances by surface and shallow subsurface short-period stations in the Middleton Place––Summerville seismic zone. The problem is difficult because it involves potential bias due to the seismic source, propagation through basement, and strong site-specific spectral modulation. Previous studies involving drilling and seismic reflection profiling indicate a 775-m thickness of sediments, with average vertical P- and S-wave velocities of 2.14 and 0.700 km/sec for the network area. The attenuation parameter kappa ({kappa}s and {kappa}p) for S and P waves is estimated from spectral analysis of the direct S and converted Sp phases. The ratio of S to Sp provides a useful check for bias. Multiple linear regression using all stations yields {kappa}s = 0.049 and {kappa}p = 0.024. The regression results are interpreted as upper-bound estimates because they assume source corner frequencies in excess of 25 Hz. A similar analysis is carried out for a hard-rock environment using reservoir-induced microearthquakes at Lake Monticello, South Carolina. From that, we estimate a maximum potential bias of 0.014 sec–1, yielding 0.035 < {kappa}s < 0.049 and 0.010 < {kappa}p < 0.024 as likely values near Charleston. We favor the lower limits of these ranges because they imply numerically similar values for the path-average quality factors (Qs = 32, Qp = 36), whereas the upper range values imply that Qs is substantially larger than Qp (Qs = 22, Qp = 15).




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M. C. Chapman, J. N. Beale, and R. D. Catchings
Q for P Waves in the Sediments of the Virginia Coastal Plain
Bulletin of the Seismological Society of America, August 1, 2008; 98(4): 2022 - 2032.
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M. C. Chapman, J. R. Martin, C. G. Olgun, and J. N. Beale
Site-Response Models for Charleston, South Carolina, and Vicinity Developed from Shallow Geotechnical Investigations
Bulletin of the Seismological Society of America, April 1, 2006; 96(2): 467 - 489.
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