Shaking Southern California

Abstract

GEOPHYSICS The Southern California Earthquake Center (SCEC) was initiated in 1991 to try to understand the physical processes of earthquakes in southern California. In its third phase, the SCEC was to study the effects of different rock sites on the amplitude of ground shaking to help improve probabilistic seismic hazard analysis. Field et al. summarize these results, which are described in fourteen papers in a special issue. Site effects may be influenced primarily by nonlinear responses of the sediments to seismic waves, or by the scattering or focusing of seismic waves by basins and other structures, or both. Refined models of the subsurface geology, the velocity structure of the crust, and the paths of seismic waves through these structures form the basis for a detailed analysis of the amplitude of ground shaking at different sites. The depth of the Los Angeles basin has the largest effect on the amplitude of the ground shaking; sites located beneath the deepest part of the basin show the strongest ground motions (highest amplitude shaking) in simulations of medium- to large-magnitude earthquakes from a range of possible sources. These data and models provide a useful synthesis of the complex site effects in southern California and what is known of the physics behind earthquakes. — LR Bull. Seism. Soc. Am. 90 , S1-S244 (2000).