ESTIMATION OF SPECTRAL ACCELERATION IN HIMALAYAN REGION USING STRONG GROUND MOTION DATA

Abstract

An estimate of expected ground motion at a given distance from an earthquake of a given magnitude is one of the fundamental inputs to earthquake hazard assessments. If a sufficient number of strong motion recordings from earthquakes and sites having similar characteristics are available then it is easy to select the assemble of these recordings for evaluating and designing structures located at these sites for seismic load. Estimation of strong ground motion parameter in this manner is referred to as site-specific. But in real cases it is not possible because of lack of data. Then a predictive mathematical model has to be developed which is called Attenuation relationship. This is expressed as a mathematical function relating to strong motion parameter, such as, peak acceleration. In this work an attenuation relationship has been developed for 5 percent damped vertical response spectra as well as horizontal response spectra using strong ground motion data recorded in Indian regions. The vertical to horizontal spectral acceleration ratio also has been determined here. The Himalayan region of India is one of the most seismically active regions in the world. Several earthquakes occurred in this area in the past. Department of Earthquake Engineering Roorkee has deployed three strong motion arrays in world's most seismically active region of the Himalayas. Thirteen earthquakes have been considered in this study for developing attenuation relationship. Mainly the earthquakes from Northeastern region, Northern region and Garhwal Himalayan region have been considered for analysis. Several attenuation relationships have been developed for different region in the world. Two types of attenuation relationship are useful for seismic hazards study, namely, Peak Ground attenuation relationship and Spectral Acceleration attenuation relationship. Spectral acceleration is better representation of an earthquake, so, 5% damped spectral attenuation relationship for Himalayan region has been developed in present thesis.