TOPOGRAPHY EFFECTS ON THE GROUND MOTION CHARACTERISTICS

Abstract

Surface topography consists of series of hills and valleys in the Himalayan region. These topographical features modify the seismic response of ground and play a crucial role in the design of life-line structures like dams, bridges etc. in the hilly areas. Spatial amplification and de-amplification of ground motion characteristics depends upon various phenomenon like focusing, de-focusing, scattering, reflection and diffraction of waves. In this paper, the response of number of triangular and elliptical ridge-valley models are simulated numerically using SH-wave. Finite difference algorithm developed Narayan and Kumar (2013) has been used to compute the SH-wave responses along the surface of the considered topography models. The response of multi-ridge- valley shows unusual and complex behaviour due to the diffraction, scattering, reflection, focusing and de-focusing of waves. The obtained ground motion level is highly different at the crest of ridge and base of valley as compared to those obtained using single ridge or valley. In multi-ridge-valley system, ground motion response for any hill or valley is influenced by its shape as well as the features of neighbouring valleys or ridges. For the same shape-ratio, more amplification is obtained at the crest of triangular ridge than elliptical ridge. The inferred complex behaviour of multi-ridge-valley topography suggests to go for even more complex topography models in order to explain the observed amplification/de-amplification pattern along the surface of topography during an earthquake.