Lapse time and frequency-dependent attenuation characteristics of coda waves in the Northwestern Himalayas

We analyzed the local earthquakes waveform recorded on a broadband seismic network in the northwestern Himalayan Region to compute lapse time and frequency dependence of coda Q (Q (c)). The observed Q (c) values increase with increasing lapse time at all frequency bands. The increase in Q (c) values with lapse time is attributed to an increase in Q (c) with depth. This implies that attenuation decreases with increasing depth. The approximate radius of medium contributing to coda generation varies from 55 to 130 km. By comparing the Q (c) values with those from other regions of the world, we find that they are similar to those obtained from tectonically active regions. The estimated Q (c) values show a frequency-dependent relationship, Q(c)=Q(0)f(n), where Q (0) is Q (c) at 1 Hz and n represents degree of frequency dependence. They represent the level of heterogeneity and tectonic activity in an area. Our results show that northwest Himalayas are highly heterogeneous and tectonically very active. Q(0) increases from 113 +/- 7 to 243 +/- 10 and n decreases from 1.01 +/- 0.05 to 0.85 +/- 0.03 when lapse time increases from 30 to 70 s. As larger time window sees the effect of deeper part of the Earth, it is concluded that Q (0) increases and n decreases with increasing depth; i.e., heterogeneity decreases with depth in the study area.