Attenuation of Coda Waves in the Saurashtra Region, Gujarat (India)

The attenuation characteristics based on coda waves of two areas—Jamnagar and Junagarh of Saurashtra, Gujarat (India)—have been investigated in the present study. The frequency dependent relationships have been developed for both the areas using single back scattering model. The broadband waveforms of the vertical components of 33 earthquakes (Mw 1.5–3.5) recorded at six stations of the Jamnagar area, and broadband waveforms of 68 earthquakes (Mw 1.6–5) recorded at five stations of the Junagarh area have been used for the analysis. The estimated relations for the Junagarh area are: Qc = (158 ± 5)f(0.99±0.04) (lapse time : 20 s), Qc = (170 ± 4.4)f(0.97±0.02) (lapse time : 30 s) and Qc = (229 ± 6.6)f(0.94±0.03) (lapse time : 40 s) and for the Jamnagar area are: Qc = (178 ± 3)f(0.95±0.05) (lapse time : 20 s), Qc = (224 ± 6)f(0.98±0.06) (lapse time : 30 s) and Qc = (282 ± 7)f(0.91±0.03) (lapse time : 40 s). These are the first estimates for the areas under consideration. The Junagarh area appears to be more attenuative as compared to the Jamnagar area. The increase in Qc values with lapse time found here for both the areas show the depth dependence of Qc as longer lapse time windows will sample larger area. 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. A comparison of the coda-Q estimated for the Saurashtra region with those of the nearby Kachchh region shows that the Saurashtra region is less heterogeneous. The obtained relations are expected to be useful for the estimation of source parameters of the earthquakes in the Saurashtra region of Gujarat where no such relations were available earlier. These relations are also important for the simulation of earthquake strong ground motions in the region.