SEISMIC BEHAVIOUR OF TRIANGULAR ALLUVIAL VALLEYS SUBJECTED TO VERTICALLY PROPAGATING INCIDENT SV WAVES

This paper is concerned with the problem of soil amplification and seismic site effects due to the local topographical and geotechnical characteristics. It focuses on 2D triangular alluvial valleys subjected to vertically propagating incident SV waves. The medium is assumed to have a linear elastic constitutive behaviour. All calculations are executed in time-domain using the spectral finite element method. Clear perspectives of the amplification patterns of the valley are presented by investigation of the frequencydomain responses. It is shown that the amplification pattern of the valley and its frequency characteristics depend strongly on its shape ratio. The maximum amplification ratio along the ground surface occurs at the center of the valley. A simple formula has been proposed for making initial estimation of the natural period of the valley in site effect microzonation studies. The natural frequency of the triangular alluvial valley decreases as the shape ratio of the valley decreases