Importance of Phasing of Strong Ground Motion in the Estimation of Structural Response

by Norman A. Abrahamson, Harding Lawson Associates, San, Francisco, CA, USA,
Jogeshwar P. Singh, Harding Lawson Associates, San, Francisco, CA, USA,

Abstract: In this paper, the influence on Fourier phase spectrum of seismic source directivity due to rupture propagation along the earthquake source is investigated. The phasing is described using frequency-dependent phase difference histograms. Strong motion recordings from the 1979 Imperial Valley earthquake are used to demonstrate the influence of directivity on phase. Significant differences are observed in the mean and variance of the phase difference histograms due to directivity for stations equidistant from the fault and located on similar soil conditions. The synthetic time histories generated for a given Boore-type Fourier amplitude spectrum, together with phase difference histograms representative of directivity effects, preserve the observed increase in the long-period spectral velocities due to directivity.

Subject Headings: Ground motion | Soil analysis | Fourier analysis | Seismic tests | Earthquakes | Seismic effects | Geological faults

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