Attenuation of High Frequency P and S Waves in Qeshm Island, Iran

Seismic waves attenuation of direct shear and P waves was investigated for the crust in Qeshm Island, using 1400 seismograms of aftershocks of the 2005 Qeshm main earthquake. The data were gathered using a seismic network consist of 17 stations. We applied the single-station method (extended coda normalization method) to analyze Qp-1 and Qs-1 using the ratio of the P and S-wave to Coda-wave amplitude spectra as a function of distance. The Qp and Qs is analyzed by using 86 lapse times of 12.5 – 97.5 seconds for center frequencies 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 16, 18, 20, 24, 28, 32 and 36 Hz. The estimated values of Qp-1 and Qs-1 decrease with increase of lapse time and distance which indicates the increase of Q-value with regard to depth. The estimated Qp-1 and Qs-1 is highly frequency dependant and decrease from 0.07 and 0.06 in 1.5 Hz to 0.003 and 0.006 in 36 Hz, respectively. Estimated Qp-1 and Qs-1 show high frequency dependence with functional form of (0.06 ± 0.003) f(-0.97 ± 0.02) and (0.1± 0.009) f(-0.83 ± 0.03), respectively. The relatively low value of Q obtained in this study agrees with the value which is expected for a seismically active and marl crust such as Qeshm.