1886 GROUND MOTION IN CHARLESTON, SOUTH CAROLINA: SCENARIOS USING FINITE RUPTURE MODELS

CHAPMAN, M. C., Dept. of Geological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24061, mcc@vt.edu.

A finite fault source model is used to simulate ground motions for scenario earthquakes near Charleston, South Carolina. The model combines theoretical crustal response for direct S waves, computed by the Thomson-Haskell method at low frequencies, with a stochastic Greens function and average source radiation pattern at high frequency. The kinematics of the faulting process is simulated using a modification of the approach described by Zeng et al. (Geophy. Res. Lett., v. 21 no. 8, 1994). The theoretical Greens function for a layered crust, used at low frequency, is replaced at high frequency (greater than approximately 1-3 Hz) by a stochastic function with decaying exponential time domain envelope shape. The duration of the low frequency motion is controlled by the faulting process and the theoretical crustal response. At high frequency, the duration is controlled by the faulting duration and an empirical adjustment for multipathing and scattering. The modeling procedure simulates the fault strike parallel and perpendicular components of horizontal motion at near fault distances. Results for Charleston involving N-NE striking faults in the 1886 meisoseismal area differ from point source simulations in the large differences between amplitude of ground velocity on the strike parallel and strike perpendicular components. Directivity effects are also potentially important for NW striking fault scenarios involving unilateral strike-slip rupture.