STUDY OF SITE EFFECTS IN KUMAON HIMALAYA USING STRONG MOTION DATA

Abstract

Kuinaon Himalayas lie in seismic zone V and therek)re are prone to large seismic risks. Stress accumulated due to constant thrusting between Eurasian plate and Indo-Australian plate. Ten stations on which I worked on are prone to high seismic activities because of reason mentioned above. The main objective of this present work is to study site effects at ten stations situated in Kumaon Himalaya by using H/V spectral ratio method and using the same for the estimation of soil bed thickness. We can get site response in terms of spectral ratio by dividing the horizontal component with vertical component recorded at the same time. Using the plot of H/V versus frequency, we can estimate the value of predominant/natural frequency, at which value of H/V is maximum. Then with the help of an equation relating soil bed thickness, predominant frequency and S wave velocity, we can find the thickness of soil bed cover. Here in this report, I tried to find out variation in site response at various places situated in Kumaon Himalaya due to changing soil conditions. By estimating the predominant frequency, we can predict the type of soil condition present there i.e. soft soil bed, stiffer soil etc. Areas having soft soil conditions are more prone to damages then the areas where stiffer soil is present. We can use this predominant frequency in designing out building/const ruct ion such that natural frequency of building does not matches with predominant/natural frequency of soil condition present there so as to avoid resonance. Results from the ten stations situated at Kurnaon I-Iimalaya on which 1 work on shows presence of soft soil condition at some stations and stiffer soil at the remaining stations. Soil bed thickness also varies with condition of soil i.e. different for stations having soft soil and stations having stiffer soil.