Abstract

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 Qα (the quality factor using P waves) and Qβ (the quality factor using S waves) have been estimated using the coda normalization method. The quality factor of coda waves (Qc) has been estimated using the single backscattering model. Multiple scattering models have been used to estimate Qi (the intrinsic attenuation parameter) and Qs (scattering attenuation parameter) for the region. The values of Qα, Qβ, Qc, Qi, and Qs show a dependence on frequency in the range of 1.5–24 Hz for the Kachchh region. The average frequency-dependent relationships (Q=Q0fn) estimated for the region are Qα=(77±2)f(0.87±0.03), Qβ=(100±4)f(0.86±0.04), and Qc=(148±3)f(1.01±0.02). The estimate of Qc is found to be higher than Qβ 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 Qc should be more than Qβ. The estimated values of Qs and Qi vary from 529 and 183 at 1.5 Hz to 3053 and 2668 at 24 Hz, respectively. We find that the Qc estimates lie between the estimates of Qi and Qs but are closer to Qi at lower frequencies. This is in agreement with the theoretical as well as laboratory measurements. A comparison between Qi and Qs shows that intrinsic absorption is predominant over scattering.

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