Attenuation characteristics of seismic waves beneath North-West Himalaya and North-East India region

Abstract

Abstract The attenuation characteristics of NW Himalaya and NE India region has been estimated using recorded accelerograms. In this analysis frequency dependent attenuation of P-wave, S wave and coda wave was estimated and the scattering & intrinsic attenuation are separated using Wennerberg (1993) method. The frequency dependent relation of scattering attenuation (QS) and intrinsic attenuation (QI) have also been developed for these seismically active regions. The frequency dependent relations for NW Himalaya are Qα = (67 ± 0.22) f (0.96 ± 0.001), Qβ = (68 ± 0.29) f (0.95 ± 0.002), QC = (107 ± 0.10) f (1.06 ± 0.0003), QI = (95 ± 0.06) f (1.01 ± 0.0002) and QS = (306 ± 6.85) f (0.80 ± 0.009) for P-wave, S-wave, coda wave, intrinsic and scattering attenuation respectively. Similarly, for NE India region the frequency dependent relations are Qα = (89 ± 0.22) f (0.85 ± 0.001), Qβ = (92 ± 0.10) f (0.86 ± 0.0004), QC = (141 ± 0.34) f (1.02 ± 0.0009), QI = (120 ± 0.21) f (0.98 ± 0.0004) and QS = (306 ± 0.66) f (0.77 ± 0.0009) for P-wave, S-wave, coda wave, intrinsic and scattering attenuation respectively. The ratio of Qβ and Qα is greater than 1 for entire frequencies range considered in this analysis which indicates that both NW Himalaya and NE India regions are partially saturated with fluids. The estimated values of intrinsic (QI) and scattering (QS) attenuation shows that intrinsic attenuation is dominant in both NW Himalaya as well as NE India region. The important fact is that in both regions’ QC lies in between QI and QS, which agrees with theoretical and experimental measurements. The frequency dependent of Q’s in this study suggests that both regions are highly heterogenous and low value of Q0’s (i.e. Qα, Qβ and QC) for both regions exhibits high degree of seismicity.