Attenuation characteristics of coda waves in Mainland Gujarat (India)

The attenuation characteristics based on coda waves of Mainland Gujarat (India) have been investigated in the present study. The broadband waveforms of 53 local earthquakes (Mw 1.1-3.3) having focal depths in the 6.0-33.6 km range recorded at five stations of Mainland Gujarat region has been used for the analysis. The frequency-dependent relationships (Q=Q(0)f(n)) for coda-Q (Q(c)) and dependency of coda-Q on lapse time windows have been determined for the said region. The average lapse time dependent coda-Q relations estimated for the region are: Q(c) = (87 +/- 13)f((1.01 +/- 0.06)) (lapse time: 30 s), Q(c) = (112 +/- 20)f((0.94 +/- 0.08)) (lapse time: 40 s) and Q(c) = (120 +/- 22)f((0.76 +/- 0.07)) (lapse time: 50 s). The increase in Q(c) values with lapse time shows the depth dependence of Q(c) as longer lapse time windows will sample larger area. The observed quality factor is strongly dependent on frequency and lapse time, which indicates that the upper lithosphere, is more heterogeneous and seismotectonically active, while the lower lithosphere is homogeneous and relatively less active. A comparison of the coda-Q estimated for Mainland Gujarat region with those of nearby Kachchh and Saurashtra regions shows that Mainland Gujarat region is more heterogeneous. The rate of decay of attenuation (Q(-1)) with frequency for the relations obtained here is found to be comparable with those of other regions of the world though the absolute values differ. The obtained relations are expected to be useful for the estimation of source parameters of the earthquakes in the Mainland Gujarat region where no such relations were available earlier. These relations are also important for the simulation of earthquake strong ground motions in the region. (C) 2012 Elsevier B.V. All rights reserved.