Attenuation of P and S waves in Western part of Iran

The aim of this study is to develop the knowledge about attenuation characteristics of seismic body waves in the west of Iran plateau using extended coda normalization method. This is an area of high seismic hazard, affecting several urban areas of larger than one million people. This study estimates the body wave attenuation in west of Iran using more than 5752 earthquake records. P-wave and S-wave attenuation were calculated in the frequency bands of 1-24 Hz. The average frequency relations of S wave have been drived Q(s) = (96 +/- 4)f((0.99 +/- 0.03)), Q(s) = (103 +/- 4)f((1.07 +/- 0.07)), Q(s) = (87 +/- 3) f((1.02 +/- 0.06)), Q(s) = (90 +/- 4) f((0.61 +/- 0.08)), Q(s) = (137 +/- 8) f((0.88 +/- 0.14)) for the whole western Iran, West of Alborz (WA), North West of Central Iran (NWCI), Sanandaj-Sirjan Zone (SSZ) and Zagros, respectively. These relations for P wave are determined as Q(p) = (56 +/- 2) f((1.12 +/- 0.05)), Q(p) = (60 +/- 1) f((0.92 +/- 0.03)), Q(p) = (49 +/- 3) f ((1.05 +/- 0.11)), Q(p) = (45 +/- 1) f((0.81 +/- 0.04)) and Q(p) = (65 +/- 8) f((1.07 +/- 0.15)). Because west of Iran is a continent-continent collision, high temperature anomaly and partial melting have caused high attenuation in the area. Presence of Sahand, Sabalan and Damavand volcanoes is a reason of warm crust and upper mantle. The low values of Q(p) and Q(s) indicate that the attenuation in the study area is comparable with other tectonically and seismically active regions. The difference between attenuation of subregions is because of the lithospheric structures and seismic activity. It is observed that the attenuation increases where the crust and upper mantle are abnormally warm. It has also been observed that the ratio of Q(s)/Q(p) is greater than 1 for frequency higher than 1 Hz, which may be due to the high degree of heterogeneity and high thermal anomalies in the region. Therefore, the results indicate the importance of contribution of the scattering attenuation to the body wave attenuation in the study area.