The Characteristics of the Short-Period S-wave Attenuation Field in the Lithosphere of Turkmenistan and Northeastern Iran and their Relation to Seismicity

The characteristics of the short-period S-wave attenuation field in the lithosphere of Turkmenistan and northeastern Iran are considered. The data obtained by the Karatau station at distances of up to 1750 km were used. The ratios of the maximum amplitudes of P-n and S-n waves (S-n/P-n parameter) were analyzed. The correlation dependence of this parameter on distance has been obtained. These data are compared with data for the regions of Caucasus, Pamir, and the Baikal Rift Zone. The West Turkmenian depression experiences significantly lower attenuation; the Turan Plate shows an intermediate level and the Alborz Range has a higher level. It is shown that attenuation in the source zones decreases considerably with time after large earthquakes. A zone of higher attenuation has been identified in the eastern Alborz Range; it is probably related to preparation of a large earthquake. The connection of heterogeneities in the attenuation field with deep-seated fluids migration is discussed.