EFFECTS OF HILLS ON SURFACE WAVES

Abstract

We have studied the effect of topography including ridge and valley on Rayleigh wave characteristics. A fourth order finite difference method is used for simulations. Gabor wavelet is used as a source time function. We have computed the seismic response of ridge and valley with different shape ratio and also by changing the geometry of the topography. Based on the analysis of simulated results, it is observed that ridge amplify the horizontal component and de-amplify the vertical component at the crest whereas valley de-amplify both the horizontal and vertical component. Amplification of horizontal component increases with increase in shape ratio and also the rate of de-amplification in case of vertical component increases with increase in shape ratio. Secondly, we have observed that after the complex interaction of Rayleigh wave with the topography splitting of the wave occurs and there is time separation between the two splits. One of the split of Rayleigh wave remain unaffected by the topography and the other passes through the flanks of the topography. This time separation increases with increase in the shape ratio. We have also analysed the seismic responses of combinations of various ridge and valley together. It can be concluded that if Rayleigh wave first interact with the valley rather than the ridge than the de-amplification occurs and the energy remained in the signal at the last stations is very negligible. Generally the amplitude of high frequency signal is nearly zero hence the valley act as a sinking zone for high frequency waves. These combinations are analysed so that we can relate the hazard associated with it and can recommend the safe location for building up the houses avoiding landslides, etc.