Estimated Ground Motions for a New Madrid Event
WOODWARD-CLYDE CONSULTANTS OAKLAND CA
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The band-limited-white-noise ground motion model coupled with random vibration theory employed in the WES-RASCAL computer program has been used to predict response spectral shapes for earthquakes in both eastern and western North America, and to generate synthetic time histories of ground motion When this method is applied to the postulated maximum time histories of ground motion. When this method is applied to the postulated maximum magnitude New Madrid event at close distances, the calculated peak acceleration is about 1.6g for hard rock outcrop motion. Extrapolations of published attenuations relationships yield similar values, but are beyond the range of the applicability of the relationships due to a lack of strong motion data for large intraplate events at very close distance to the rupture surface. Realistic appearing synthetic acceleration, velocity, and displacement time histories were generated by combining the Fourier amplitude spectrum predicted by the band- limited-white-noise model with the Fourier phase spectrum from ground motion recorded above the source area of the 19 September 195 Michoacan, Mexico earthquake. The effects of a generic deep soil profile, appropriate for the central United States, upon the computed outcrop motion are examined. Both linear and equivalent-linear analyses are performed using a frequency domain wave propagation code. Response is computed for different models of the variation of shear-wave damping with strain. Results indicate that the strain dependency of the shear-wave damping is a controlling factor of the computed response.