Strong Motion Seismology

Abstract

Strong motion seismology is defined and placed in context with Seismology and Earthquake Engineering. Current methods and techniques are outlined, along with the main results obtained, with emphasis on the implications for the basic problems of seismic risk zoning. Under experimental methods, attention is given to the basic characteristics of modern strong motion accelerographs, and major results obtained are summarized. Simplified instrumentation is briefly described, and current strong motion networks are outlined, with comments on problems of site selection and economics of network design. Current data processing techniques for strong motion accelerograms are discussed and modern improvements in data recovery capabilities are described. Distribution of local strong ground motions as measured during the 1971 San Fernando earthquake are discussed, and spectral properties of strong ground motion are given for some recent investigations at the El Centro, California, accelerograph site. Comments are made on non-instrumental seismology, intensity scales, and isoseismal maps. Recent theoretical work on seismic source parameters is summarized, and determinations of such parameters as seismic moment and stress drop from far-field and near-field spectra are discussed. Implications of source multiplicity for earthquake engineering problems are pointed out. The importance of transmission path effects on local distribution of strong ground motions is emphasized, and examples are given of the influence of surface topography, subsurface nonuniformities, and layer boundaries on surface motion. Some comments are made on the influence of instrument characteristics and data processing on accelerogram characteristics. Some factors involving geologic faults and earthquakes are discussed, with an evaluation of the relationship between faults and seismic hazards.

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