1897 Bulletin of the Seismological Society of America, Vol. 96, No. 5, pp. 1897–1914, October 2006, doi: 10.1785/0120050144 Shear-Wave Velocity and Seismic Response of Near-Surface Sediments in Charleston, South Carolina by Ronald D. Andrus, Cedric D. Fairbanks, Jianfeng Zhang, William M. Camp III, Thomas J. Casey, Timothy J. Cleary, and William B. Wright Abstract Six major geologic units in Charleston, South Carolina, are character- ized in terms of shear-wave velocity (V S ) in this article. The characterization is based on in situ V S measurements at 91 sites. The six units are man-made fills, Holocene and late Pleistocene deposits, the Wando Formation, the Ten Mile Hill beds, the Penholoway Formation and the Daniel Island beds, and Tertiary deposits. Median V S values for these units in the top 25 m are 145, 111, 189, 176, 285, and 399 m/ sec, respectively. For Tertiary deposits in the depth intervals of 25–55 m, 55–75 m, and 75–100 m, median V S values are 435, 533, and 663 m/sec, respectively. A seis- mic-response parametric study is conducted assuming several soil/rock models and two input rock outcrop motions with peak accelerations of 0.3g and 0.1g. It is found that Quaternary sections with V S of 190 m/sec (e.g., the Wando Formation) and thicknesses of about 7 m to 15 m exhibit predominant peaks in the acceleration- response spectra at periods of about 0.25 to 0.4 sec. These predominant peaks match fundamental periods of many existing buildings in the old city district of Charleston. The results suggest that local site conditions contributed to building damage in the 1886 Charleston earthquake. Introduction Charleston, South Carolina, is the second most seismi- cally active region in the eastern United States, after the New Madrid seismic zone. The 1886 Charleston earthquake dam- aged numerous buildings and resulted in about 60 deaths (Bollinger, 1977). Recent estimates of earthquake moment magnitude, M w , for the 1886 event range from 6.9  0.3 (Bakun and Hopper, 2004) to 7.3  0.3 (Frankel et al., 2002). Based on paleoliquefaction studies conducted during the past 20 years, Talwani and Schaeffer (2001) estimated a recurrence rate between 500 and 600 years for magnitude 7 earthquakes near Charleston and about 2000 years for magnitude 6.0 events near Georgetown and Bluffton, South Carolina. This evidence led the U.S. Geological Survey in 1996 and 2002 to map significantly higher expected ground- shaking levels for Charleston than indicated on previous na- tional maps, with the 2002 levels even higher than the 1996 levels (http://geohazards.cr.usgs.gov/eq/). A repeat of the 1886 earthquake, or even a smaller moderate event, could be devastating to Charleston and the surrounding region (e.g., FEMA, 2000; Silva et al., 2003; Wong et al., 2005). Wong et al. (2005) estimated that a future repeat of the 1886 earthquake could result in 900 deaths, more than 44,000 in- juries, and a total economic loss of $20 billion in South Carolina alone. Several studies have identified small-strain, shear-wave velocity (V S ) as a primary controlling factor for site response during earthquake ground shaking (e.g., Seed et al., 1976; Idriss, 1990; Borcherdt, 1994; Boore et al., 1994; Joyner et al., 1994; Midroikawa et al., 1994). Seed et al. (1976) and Idriss (1990) observed distinct differences in average re- sponse spectral shapes of sites with different subsurface con- ditions. The differences in spectral shapes result from ver- tical variations in soil material properties and strongly depend on V S of the near-surface materials. The determinant effect of V S on ground motion has lead to new site coeffi- cients and classification system used in recent building seis- mic code provisions (Dobry et al., 2000). Because V S is an important engineering property for earthquake ground-shaking prediction, several efforts to compile V S measurements and other geotechnical informa- tion from sites in the greater Charleston area have been ini- tiated in recent years (e.g., Silva et al., 2003; Andrus et al., 2003; Zhang, 2004; Zhang et al., 2004; Fairbanks et al., 2004; Chapman et al., 2006). The conference paper by Zhang et al. (2004) presents composite plots of V S profiles and characterizes average V S in the top 30 m for four major surficial geology groups. The data report by Fairbanks et al. (2004) provides electronic files of V S and Cone Penetration Test (CPT) measurements from the Charleston quadrangle. In this article, characteristic V S properties of six major