Accession Number : AD0781490

Title :   State-of-the-Art for Assessing Earthquake Hazards in the United States Report 3. Factors in the Specification of Ground Motions for Design Earthquakes in California,

Corporate Author : ARMY ENGINEER WATERWAYS EXPERIMENT STATION VICKSBURG MISS

Personal Author(s) : Hofmann,Renner B.

Report Date : JUN 1974

Pagination or Media Count : 103

Abstract : Accelerations of 0.4g to over 1.0g from earthquakes of magnitudes 4.5 to 6.5 have been recorded near their sources. In practice, design earthquake procedures extrapolate recorded data, usually to within a few miles of the source fault. The bases for these extrapolations either are purely statistical or are contingent upon assumed time functions of fault displacement. When modified to account for fault dislocation, curves of maximum acceleration at a predominant period versus magnitude and depth adequately predict peak accelerations near the source as well as at a distance. Peak accelerations occur only during a fraction of the duration of high-amplitude shaking and attenuate more rapidly with distance than the general level of high accelerations. Peak accelerations at 10 Hz appear to be limited by the effective stress locking a fault just prior to the time of rupture. Peaks up to 2.0g may or may not occur and are essentially independent of magnitude. Topography, absorption, and transmission of seismic energy through sedimentary layers are shown to have frequency- and distance-dependent effects on the resulting shaking at the surface. Duration of shaking and distortions of the surface in areas of sedimentary cover are also shown to be important considerations in the specification of design earthquakes. (Modified author abstract)

Descriptors :   *Earthquakes, *Hazards, *Ground motion, *California, Seismic waves, Faults(Geology), Shear stresses, Epicenters

Subject Categories : Seismology

Distribution Statement : APPROVED FOR PUBLIC RELEASE