INTEGRATION OF HISTORICAL EARTHQUAKE DAMAGE INFORMATION INTO SEISMIC HAZARD MAPPING AND SITE PLANNING FOR ADVANCED NATIONAL SEISMIC SYSTEM STATIONS, CHARLESTON, SOUTH CAROLINA

The Charleston, South Carolina region was the site of an M ~ 7 earthquake on August 31, 1886, the largest historical earthquake in the southeastern USA. Although this earthquake occurred prior to instrumental earthquake recording, detailed information on its effects exist in the form of insurance reports and maps of earthquake building damage. Previous workers (e.g., Robinson and Talwani, BSSA 73, 1983) have used this information to produce simplified maps of the distribution of earthquake damage and compare it to surface geologic conditions. We are in the process of updating this work using modern GIS technology to accurately georectify historical building locations with their current locations in modern Charleston and combine this information with geologic, soil property, flood hazard, etc., maps of the region. The goals of this work are: a) to produce a “ground truth” dataset of building damage and geologic site conditions for use in verifying results of seismic hazard and vulnerability studies in Charleston, b) to guide efforts to map near surface seismic velocities for future detailed seismic hazard studies, and c) to support site planning for Advanced National Seismic System (ANSS) strong motion seismometer stations. This presentation documents the efforts to collect and integrate existing historical data into the GIS system and presents how this GIS based data has been used to help emplace seismographs for the ANSS program. The historical information has already been used to guide the choice of locations of some ANSS sites, in turn; the data that has been returned from the seismometers is already yielding results. One ANSS site on the campus of The Citadel (C2SC) was chosen to be representative of the many artificially filled tidal creek channels that exist in Charleston. Geologically similar locations were sites of extensive damage in the 1886 earthquake. The other ANSS site at The Citadel (C1SC) is located on largely unmodified Pleistocene near shore deposits approximately 500 meters away from C2SC. Accelerograms from the November 11, 2002 M=4.2 offshore South Carolina earthquake show significant (~50%) amplification of ground motion at C2SC relative to C1SC, reflecting the usefulness of using historical information in choosing these sites.