Seismic Wave Absorption in the Eastern Part of the North Caucasus Estimated from Records by Seismic Station “Makhachkala”

Abstract

Abstract—Records of local earthquakes obtained at seismic station “Makhachkala” are used for estimating the frequency-dependent quality factor of the Earth’s crust and upper mantle in the eastern part of the North Caucasus. The records of 42 earthquakes with epicentral distances up to ~200 km and magnitudes M ~ 2.4–5.8 have been analyzed. The quality function Q(f) is estimated by coda normalization method which is applicable in different situations and yields reliable Q(f) estimates. With the assumed three-segment geometrical spreading function that is equal to 1/R at distances from 1 to 50 km from the source, 1/50 at distances 50–150 km, and 1/ $$\sqrt R $$ beyond 150 km, the quality factor is found to be Q(f) ~ 10 f 0.9, which is close to the Q-values previously established for the the medium in the vicinity of Sochi, Anapa, and Kislovodsk. The obtained quality factor estimates can be used for forecasting the parameters of ground motions during the future strong earthquakes in the eastern part of the North Caucasus. In the future studies, these estimates can be refined.