ESTIMATION OF Q (QUALITY FACTOR) IN SIKKIM HIMALAYAN REGION USING LOCAL EARTHQUAKES

Abstract

The Quality Factor using coda waves to find the attenuation of seismic wavefonn generated by any earthquake event was analyzed and studied for the Sikkim Himalayan region by using the data collected from the broadband seismological network recorded in the year 2011 and 2012, recorded by Wadia Institute of Himalayan Geology, Dehradun. The comprehensive study is done for the analysis of 132 local events recorded at 7 stations with the epicenter in the Sikkim Himalayan region with the focal depth ranging from I kin to 70 km and 1 .5<ML<S.S. The value Quality factor Q using the coda waves was estimated by using a Coda window intervals of 25 sec, 35 sec. 45 sec, 50 sec respectively at different central frequency vary from 2 to 16 and then after we do the averaging of this coda-q value at different central frequency for each coda window interval. The average value of Qc for the study region varies from 156 at 2 Hz to 1392 at 16 Hz for window length of 25 seconds. When window length is 35, Qc, is 236 at 2 Hz and 1531 at 16 Hz. Higher values of Qc are obtained at 45 and SOs window lengths. This observation which clearly indicating that the value of the Qc depending on frequency is due to the degree of heterogeneity present in the medium and level of seismic (or tectonic) activity in the study area (Aki 1980) and by comparing with other reason we can say that Sikkim Himalayan region is seismically (or tectonically) highly active region.