Regional variation of coda Q in Kopili fault zone of northeast India and its implications

Abstract

Kopili fault has been experiencing higher seismic and tectonic activity during the recent years. These kind of active tectonics can be inspected by examining coda-wave attenuation and its dependence with frequency. Exploiting single back-scattering model, we have endeavored to measure coda Q and its associated parameters such as frequency dependent factor (n) and attenuation coefficient (γ) covering seven lapse-time windows spanning from 30 to 90s and central frequencies 1.5, 3.5, 6, 9 and 12Hz. The average estimated values of QC increases with frequency and lapse time window from 114 at frequency 1.5Hz to 1563 at frequency 12Hz for 30s window length, and from 305 at frequency 1.5Hz to 2135 at frequency 12Hz for 90s window length. The values of Q0 and n are also estimated for the entire Kopili fault zone. For this study region, the Q0 values vary from 62 to 348 and n varies from 0.57 to 1.51 within the frequency range 1.5 to 12Hz. Furthermore, depth variation of attenuation of this region reveals that there is velocity anomaly at depth 210–220km as there arises sharp changes in γ and n which are supported by available data, reported by other researcher for this region. Finally, we have tried to separate the intrinsic and scattering attenuation for this area. It is observed that the entire region is dominated by mainly scattering attenuation, but we can see an increase in intrinsic attenuation with depths in two stations namely TZR and BKD. Furthermore, the obtained results are comparable with the available global data.