Spatial variations of coda-wave attenuation in the Khurgu region, south-east of the Zagros from analysis of local earthquakes

Abstract

In this study, we estimate the characteristics of coda-wave attenuation in the Khurgu region, southeast of Zagros, with the use of single-back scattering procedure. The selected database comprises of 4870 seismograms of 259 local earthquakes recorded from March to June 2006, at 25 seismic stations within 2–100 km of epicentral distance, depth range 4–25 km, and 2–4.7 local magnitude range. oda attenuation analyzed on narrow bandpass-filtered seismograms from the time-domain decay of coda-wave amplitudes. The intended frequency-band ranged from 0.5 to 24.0 Hz.Moreover, coda Q values have been estimated by using different window length, from 5 to 50 s. The coda Q value shows frequency decency in the form of Qof n.The mean-frequency relation for the above region has been found to be Qc = 29 ± 1.0f 1.13±0.007 for the 5-sec lapse-time window length as well as Qc = 147 ± 1.4f 0.99 ±0.045 for the 50 s lapse time window length.The Qc value has been estimated at 25 stations and its lateral variation has been analyzed in this study. The distinct Coda Q values were observed at separate stations between the southern and northern regions. Our observations showed major differences in the coda depth. In addition, Coda Q values in the northern part are lower than southern part at all depths.Beneath south and north of High Zagros Fault (HZF), the increase rate of Qc has been higher at the depth 70 and 80 km, respectively. This may indicate the presence of the increased attenuation anomaly beneath the area lithosphere.