Quality Estimates of the Crust and Upper Mantle of the Northeast Caucasus Based on to Makhachkala Seismic Station Records

Abstract

This article continues research of the seismic wave propagation parameters in the North Caucasus. The Q factors of the crust and upper mantle in the vicinity of Makhachkala are obtained, which are compared with the previously obtained Q factors in the vicinity of Sochi, Anapa, and Kislovodsk. According to records of regional (with epicentral distances up to ~300 km) earthquakes (MW ~ 3.9–5.6) acquired by the Makhachkala seismic station, estimates are obtained for the Q factor of the medium Q (f) in the form Q (f) ≈ f0.98 (envelope method) and Q (f) ≈ 135f0.72 (by coda normalization method); the generalized estimate has the form Q (f) ≈ 120 f0.8 (at frequencies up to ~ 16 Hz). The obtained Q factors in the vicinity of Makhachkala at low frequencies are slightly higher than the estimates obtained for regions of the Northwest Caucasus: the environs of Sochi, Anapa, and Kislovodsk (Q0 ~ 55–90; n ~ 0.7–1.0). The obtained Q factor estimates are planned to be checked and, possibly, refined by stochastic modeling of local earthquake records.