Effects of Layered Stochastic Soil Profile on the Coherency Functions of Spatially Variable Seismic Ground Motions: Case Study Nw Algeria


Abstract eng:
Seismic design of common engineering structures is based on the assumption that excitations at all support points are uniform or fully coherent. However, in lifeline structures with dimensions of the order of wavelengths of incident seismic waves, spatial variation of seismic ground motions caused by incoherence effects and stochasticity in the characteristics of the surface layers may introduce significant additional forces in their structural elements. The main objective of this paper is to provide estimates of coherency functions of spatially variable ground motion at the free surface of a layered stochastic soil sites in the epicentral region of the El-Asnam Earthquake in Algeria. Lagged coherency functions at bedrock have been estimated in [1] by simulating ground motion field (around Sogedia Factory) corresponding to the 1980 El-Asnam Earthquake. Considering randomness in the thickness of soil layers overlying the bedrock in the study area, an analytical approach proposed by Zerva and Harada [2] is used to evaluate lagged coherency functions at the surface. Soil proprieties are assumed to vary laterally with a Gaussian distribution. Contribution of various factors such as damping ratio of the soil, soil predominant frequency and its spatial variation, and wave propagation velocity on lagged coherency in the surface are investigated. Numerical results indicate that spatial coherence of surface motion is similar to that of bedrock motion, except at the predominant frequency of the site, where a sharp decrease in lagged coherency is observed. It is also observed that, even for firm soil conditions, later homogeneity of site can significantly affect lagged coherency of motion at ground surface.

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Conference Title:
Conference Title:
16th World Conference on Earthquake Engineering
Conference Venue:
Santiago (CL)
Conference Dates:
2017-01-09 / 2017-01-13
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 Record created 2017-01-18, last modified 2017-01-18


Original version of the author's contribution as presented on USB, paper 3633.:
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