Lapse time and frequency-dependent attenuation characteristics of Kumaun Himalaya

We have analyzed local earthquake data set consists of 84 well located events, recorded by a digital seismic network in the Kumaun Himalaya region during 2004–2007 to study seismic attenuation characteristics of the region. Single back-scattering assumption is used to estimate coda Q (Qc) values of the region at frequency range of 1.5, 3, 6, 8, 12 and 18 Hz for different lapse time window length. The values of Qc show a ubiquitous observation of frequency dependence and follow a substantially similar trend as observed in other tectonically active parts of the Himalaya. The lapse time dependencies of coda waves are investigated which reveal that by increasing lapse time window from 20 to 50 s, Q0 (Qc at 1 Hz) increases from 64 ± 2 to 230 ± 19 while frequency dependent parameter n decreases from 1.08 to 0.81. Increase in Qc with lapse time indicates decrease in heterogeneity with depth. The observed values of Q0 and n infer that the medium beneath the study area is highly heterogeneous and tectonically very active. The variation of Qc with lapse time at 1.5 Hz follow a similar pattern with the theoretically predicted values of Gusev (1995) although the frequency parameter n does not match with the model. It may suggest that the turbidity decays rapidly with depth for the Kumaun Himalaya. Our results are comparable with those obtained from tectonically active regions in the world.

► An attempt is made to understand the frequency and lapse time dependence of attenuation characteristics of Kumaun Himalaya.
► The result indicates that the crust in the study area is highly heterogeneous and tectonically very active.
► Strong frequency dependence behavior is observed for this region which could be related to the size of heterogeneities.
► Increase in Qc values with the lapse time suggests that the deeper crust is less heterogeneous than the shallower part.
► We find turbidity decays rapidly with depth for Kumaun Himalaya which is apparent for other parts of Himalaya.