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Influence of local geology on earthquake ground motion

Tsai, N. C. (1969) Influence of local geology on earthquake ground motion. California Institute of Technology . (Unpublished) http://resolver.caltech.edu/CaltechEERL:1969.EERL.1969.002

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Abstract

As a simplified approach for estimating theoretically the influence of local subsoils upon the ground motion during an earthquake, the problem of an idealized layered system subjected to vertically incident plane body waves was studied. Both the technique of steady-state analysis and the technique of transient analysis have been used to analyze the problem. In the steady-state analysis, a recursion formula has been derived for obtaining the response of a layered system to sinusoidally steady-state input. Several conclusions are drawn concerning the nature of the amplification spectrum of a nonviscous layered system having its layer stiffnesses increasing with depth. Numerical examples are given to demonstrate the effect of layer parameters on the amplification spectrum of a layered system. In the transient analysis, two modified shear beam models have been established for obtaining approximately the response of a layered system to earthquake -like excitation. The method of continuous modal analysis was adopted for approximate analysis of the models, with energy dissipation in the layers, if any, taken into account. Numerical examples are given to demonstrate the accuracy of the models and the effect of a layered system in modifying the input motion. Conditions are established, under which the theory is applicable to predict the influence of local subsoils on the ground motion during an earthquake. To demonstrate the applicability of the models to actual cases, three examples of actually recorded earthquake events are examined. It is concluded that significant modification of the incoming seismic waves, as predicted by the theory, is likely to occur in well defined soft subsoils during an earthquake, provided that certain conditions concerning the nature of the incoming seismic waves are satisfied.


Item Type:Report or Paper (Technical Report)
Additional Information:PhD, 1969
Group:Earthquake Engineering Research Laboratory
Record Number:CaltechEERL:1969.EERL.1969.002
Persistent URL:http://resolver.caltech.edu/CaltechEERL:1969.EERL.1969.002
Usage Policy:You are granted permission for individual, educational, research and non-commercial reproduction, distribution, display and performance of this work in any format.
ID Code:26507
Collection:CaltechEERL
Deposited By: Imported from CaltechEERL
Deposited On:20 Feb 2008
Last Modified:26 Dec 2012 13:59

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