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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
Authors: Hofmann, Renner B.
Keywords: Earthquakes
Earthquake risk
Earthquake hazards
Mathematical models
Numerical models
Publisher: Soils and Pavements Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Description: Miscellaneous Paper
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. Inverse digital filtering is recommended as a method to incorporate the desired characteristics into real or synthetic strongmotion seismograms to represent the expected shaking at a particular site. Spectra of design earthquakes should be smooth to ensure that the natural frequency of a particular structure or structural element does not correspond to a fortuitous trough in the spectra of a particular design earthquake. Fault length may be used to estimate the maximum possible rupture length and hence potential magnitude M. Where geodetic measurements of regular fault slip on faults such as the San Andreas are available, potential magnitudes can be calculated as a function of time. Such calculations indicate a potential M = 8.1 earthquake near San Francisco and M = 8.4 near the Los Angeles area at this time (1974).
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Miscellaneous Paper

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