Characteristics of seismic wave attenuation in the crust and upper mantle of the Northern Caucasus |
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| Authors: | O V Pavlenko |
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| Institution: | (1) Schmidt Institute of Physics of the Earth (IPE), Russian Academy of Sciences (RAS), Bol’shaya Gruzinskaya ul. 10, Moscow, 123995, Russia |
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| Abstract: | The quality factor Q as a function of frequency in an S wave range of 1–8 Hz is estimated from records of ～60 earthquakes (M w > 3.9 and source depths of 1–60 km) obtained at the Sochi seismic station at epicentral distances of less than ～300 km. Methods of Q estimation used in the paper were developed in works by Aki, Rautian, and others; they are based on the suppression of source-related and local effects in S wave spectra with the help of coda waves measured at a fixed time from the first arrival. To compensate for directivity effects, averaging was performed over the set of events whose sources were located in a wide range of back azimuths. The geometric divergence is represented as a three-segment function: 1/R, 1, and 1/√R at epicentral distances of 1/50–1/70 to 50–70 km, 50–70 to 130–150 km, and greater than 130–150 km, respectively. The geometric divergences in this model yielded the following estimates of the quality factor: Q(f) ～ 80f 0.9 with a base of 35–280 km and Q(f) ～ 110f 0.8 with a base of 60–280 km. The resulting combinations of the propagation path effects (Q and the geometric divergence) can be used for predicting strong motion parameters in the Northern Caucasus. |
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