On Earthquake Ground Motion and Structural Response in Alluvial Valleys

: This paper is concerned with the problem of soil amplification and structural damage due to local site conditions in sedimentary valleys during earthquakes. It focuses on a small valley in Kirovakan, for which one dimensional (1D) wave propagation analyses have failed to provide adequate answers for the large extent and spatial distribution of damage during the 1988 Armenia Earthquake. A more realistic two-dimensional finite element analysis is performed herein in search of an explanation for the observed behavior. Using as input an inferred rock accelerogram, the response of the valley is calculated for a vertically incident SH-wave. Synthetic accelerograms of the surface ground motion are presented for different sites; these accelerograms are then used to determine the amplification ratios of the surface response with respect to that of the free-field motion of the rock outcrop, for different frequencies and for a continuous set of sites. In addition, response spectra are evaluated..