Attenuation of high-frequency seismic waves in Kachchh region, Gujarat, India

The attenuation properties of the crust in the Kachchh region, Gujarat, India, have been investigated. For this purpose, 49 local earthquakes having focal depths in the 3-38 km range have been used. The quality factors Q(alpha) (the quality factor using P waves) and Q(beta) (the quality factor using S waves) have been estimated using the coda normalization method. The quality factor of coda waves (Q(c)) has been estimated using the single backscattering model. Multiple scattering models have been used to estimate Q(i) (the intrinsic attenuation parameter) and Q(s) (scattering attenuation parameter) for the region. The values of Q(alpha), Q(beta), Q(c), Q(i), and Q(s) show a dependence on frequency in the range of 1.5-24 Hz for the Kachchh region. The average frequency-dependent relationships (Q = Q(0)f(n)) estimated for the region are Q(alpha) = (77 +/- 2)f((0.87 +/- 0.03)), Q(beta) = (100 +/- 4)f((0.86 +/- 0.04)), and Q(c) = (148 +/- 3)f((1.01 +/- 0.02)). The estimate of Q(c) is found to be higher than Q(beta) in this region. This analysis supports the Zeng et al. (1991) model that predicts that the effects of intrinsic and scattering attenuation combine in a manner that Q(c) should be more than Q(beta). The estimated values of Q(s) and Q(i) vary from 529 and 183 at 1.5 Hz to 3053 and 2668 at 24 Hz, respectively. We find that the Q(c) estimates lie between the estimates of Q(i) and Q(s) but are closer to Q(i) at lower frequencies. This is in agreement with the theoretical as well as laboratory measurements. A comparison between Q(i) and Q(s) shows that intrinsic absorption is predominant over scattering.