Characteristics of body-wave attenuations in the Bhuj crust

Abstract

The frequency-dependent attenuations of P and S waves in the crust beneath Bhuj are estimated using the extended coda-normalization method for varying the exponent, γ, in the geometrical spreading function, rγ (r is the hypocentral distance). The analysis is based on the measurement of 378 aftershocks of the 2001 Bhuj earthquake (Mw 7.6). The events were recorded by six stations of the network in the frequency range of 1-24 Hz. The values of QP1 and QS1, corresponding to spectral amplitude decays, show strong frequency dependence and are expressed as 0:052 0:019 f 1:1 0:06 and 0:02 0:01 f 1:0 0:04, respectively, when γ is fixed at unity. The ratio QP1=QS1 is found to be larger than unity for the whole frequency range. A model of random heterogeneity characterized by an exponential autocorrelation function with a root mean square fractional fluctuation ε of 6%-8%, a correlation length a of 0.4-1.2 km, and ε2/a ≈ 10 2-10 3 km for the frequency range from 1 to 24 Hz can simulate the observed attenuation properties. This suggests that a scattering model well reproduce the frequency-dependent characteristics of QP1 and QS1 obtained in Bhuj.