Frequency and lapse time dependent seismic attenuation in eastern Himalaya and southern Tibet

Abstract

We have studied the attenuation characteristics of eastern Himalaya and southern Tibet by using local earthquake data set that consists of 123 well-located events, recorded by the Himalayan Nepal Tibet Seismic Experiment operated during 2001–2003. We have used single backscattering model to calculate frequency-dependent values of coda Q ( $$Q_\mathrm{c}$$ ). The estimation of $$Q_\mathrm{c}$$ is made at central frequencies 2, 4, 8 and 12 Hz through five lapse time windows from 10 to 50 s starting at double the travel time of the S-wave. The observed $$Q_\mathrm{c}$$ is found to be strongly frequency-dependent and follows a similar trend as observed in other tectonically active parts of the Himalaya. The trend of variation of $$Q_\mathrm{c}$$ with lapse time and the corresponding apparent depths is also studied. Increase in $$Q_\mathrm{c}$$ values with the lapse time suggests that the deeper part of the study region is less heterogeneous than the shallower part. The observed values of $$Q_0$$ ( $$Q_\mathrm{c}$$ at 1 Hz) and frequency parameter n indicate that the medium beneath the study area is highly heterogeneous and tectonically very active. A regionalization of the estimated $$Q_0$$ is carried out, and a contour map is prepared for the whole region. Some segments of Lesser Himalaya and Sub-Himalaya exhibit very low $$Q_0$$ , while the whole Tethyan Himalaya and some parts of Greater Himalaya are characterized by low $$Q_0$$ values. Our results are comparable with those obtained from tectonically active regions in the world.