Examination of earthquake intensity increments in side zones of valleys with alluvial basins by an analytical approach and a model experiment

The effect of topography on the seismic wave motion has been of interest to many studies. In this study, the earthquake intensity increments (amplification) in side zones of valleys with alluvial basins were investigated using finite element method and model experiments. In the study, finite element models of valleys, one of which with a triangular cross section, and the rest with trapezoidal cross sections, with five different side slopes (17º, 22º, 27º, 37º, 45º) were formed. The accelaration-time histories obtained by the commercial finite element code (QUAD4M) at the valley sides, valley edges, and at intermediate points were converted to Fourier Amplitude Spectrums. The amplitude-frequency variations obtained at the three selected points of the valley as well as at the bedrock were investigated in each of the four selected phases of the earthquake time history. As a result of the performed dynamic analysis, the effect of the valley slope variation at three different points on the valley was examined at four separate phases of the earthquake time history. In addition, laboratory model experiments were performed using two different materials. In the first model, in order to represent the infinite rigidity assumed in the dynamic analyses, the model bedrock was formed of plaster. On the other hand, in the second model, the model bedrock was made up of a silicon-sand mixture to obtain elastic properties closer to those in the nature. For both models, the alluvial basin was represented by a material of gel-like consistency, obtained by mixing polyvinyl alcohol solution with borax (sodyumtetraborat ? Na2B4O7) solution in predetermined proportions. By producing sinusoidal waves in various frequencies, accelelaration time history measurements and correlations were performed on the models, at the same three points that were selected in the finite element analyses. The results obtained from the model experiments were compared with those obtianed from the finite element analyses.Science Code: 911.1.050Key Words: Effects of topography, slope of valley, seismic reflectionPage Numbers: 127Adviser: Prof. Dr. Süleyman PAMPAL