A study of characteristics of ground motion response spectra from earthquakes recorded in NE Himalayan region: an active plate boundary

摘要

In the present work, acceleration response spectra are determined from earthquakes which have occurred in the NE region and the effect of local geology on its shape is studied. One hundred and ninety-five strong ground motion time histories from 45 earthquakes which have occurred in the NE region having a magnitude range of 3.5 aecurrency sign Mw aecurrency sign 6.9 and a distance range of 20-600 kms are used. It is observed that the shape of the normalized acceleration response spectra is influenced by the local site conditions and regional geology. The influence of magnitude and distance on the spectra is also studied. The present study is carried out for three categories of rocks: Pre-Cambrian, Tertiary and Quaternary. It is inferred that the acceleration response spectra in the current Indian code designed for the entire country are applicable for NE region as it is within the spectral limits prescribed in Indian code. The ground motion is amplified at higher frequencies for stations located on hard rock, while for stations located on alluvium sites, it is amplified at lower frequencies. The sites located on hard rock show lowest values of spectral acceleration than the sites located on alluvium sites. The results obtained in the present study are compared with the similar results obtained in the stable continent region like Gujarat. It is found that the dominating period of response spectrum of similar rock types is found to be at higher side for NE region as compared to Gujarat region. This may be attributed towards the tectonic complexity of the NE region than the stable continent region like Gujarat.