ESTIMATION OF SITE AMPLIFICATION IN - ARUNACHAL HIMALAYA USING CODA WAVES OF LOCAL EARTHQUAKES

Abstract

Amplitudes of seismic waves increase significantly as they pass through soft soil layers near the earth's surface. This phenomenon, known as site amplification, play an important role in influencing varying degree of damage to the structures even up to collapse of the structure. Therefore, it is very essential to account site amplification estimation for while designing structures on any strata. Site amplification effects condition the occurrence of damages in moderate to large earthquakes. Therefore, it has received much attention during the last two decades. Hence. the results of the site response studies for local earthquakes occurring in an area are one of the most important inputs for seismic hazard assessment of a region. Site Amplification Characteristics using Coda-wave is estimated for the local earthquakes of - Lower Slang of Arunachal Himalaya at five stations that form the seismological network around a dam site in Lower Siang region at various frequencies. Coda-wave spectral ratios were computed from 60 waveforms in the frequency range I Hz to 12 Hz considering ADI-PASI located on the rock as a reference site, and also relative to a reference site which is an average ol'all sites. From Coda-wave spectral ratios. higher amplifications have been found out at sites located nearest to the epicenters of the local earthquakes as compared to sites located away from the epicenters. Almost similar frequency dependent trends in the Coda-wave site amplifications in the radial and transverse components have been found at the majority of' sites relative to reference site. However, the vertical components show consistently low site amplifications as compared to horizontal components particularly above 3 Hz to 6 Hz.