Lateral variation of crustal attenuation properties from southern Tibet to eastern Nepal Himalaya

Lateral variations of body wave, coda wave, intrinsic and scattering attenuation have been investigated using 114 local earthquakes which were recorded in eastern Nepal Himalaya and southern Tibet from October 2001 to March 2003. The extended coda normalization method and single isotropic scattering model are used to estimate the quality factor of body waves (Q(p), Q(s)) and coda wave (Q(c)), respectively. We have divided the entire area into two zones such as eastern Nepal Himalaya and southern Tibet to explore the attenuation characteristics laterally. We have used all crustal events within hypocentral distance of 100 km. The observations are made at six different central frequencies such as 2, 4, 6, 8, 10 and 12 Hz. For both regions Q values are found to be frequency dependent. Subsequently, we separate out the contributions of both intrinsic (Q(i)) and scattering (Q(sc)) attenuation parameters using the Wennerberg approach. It is observed that the intrinsic attenuation prevails over scattering attenuation in eastern Nepal Himalaya at all the frequency ranges while for southern Tibet scattering attenuation dominates at higher frequencies (>8Hz). The similarity between Q(c) and Q(i) is noted for both areas, which confirms that the decay of coda wave is primarily due to the intrinsic dissipation. Intrinsic attenuation is found to be higher in southern Tibet, which could be associated with the partial melting, fluid trapped in the crust or high heat flow that exists below the region. The results correlate with the underlying geo-tectonical model as well as with the structural complexities present beneath the study area. The obtained values in this study are well comparable with other results reported for similar tectonic regime.