Seismogenic zones of the Transcaspian region: Characteristics of sources of the largest earthquakes. II. The Krasnovodsk and Kazandzhik earthquakes

Abstract

An interpretation of the source origin of the largest Transcaspian Kazandzhik 1946 and Krasnovodsk 1895 earthquakes is proposed. The interpretation is based on the analysis of data on the geological structure of the Transcaspian region and the available evidence for coseismic effects of these events. Data on other earthquakes of the region and the results of focal mechanism determinations are taken into account. The Kazandzhik earthquake consisted of two shocks with separate sources. The source of the first, weaker shock, located in structures of the Greater Balkhan Ridge, was characterized by reversed-strike-slip motions. The 40–50-km-long source of the second, main shock, which determined the earthquake magnitude (M ∼ 6.9–7.0), was located in the Kazandzhik basin, in the boundary zone between the Kopet Dagh foredeep and the Frontal anticlinal range. It was similar in type and coseismic effects to the source of the Ashkhabad earthquake of 1948. The Krasnovodsk earthquake source 100–120 km long, located in the crust, is associated with the development of the Balkhan foredeep. In accordance with the source size, the magnitude of the Krasnovodsk earthquake is M ∼ 7.8–8.0. The three major earthquakes (Ashkhabad, Kazandzhik, and Krasnovodsk) in the Transcaspian region are associated with the general tectonic process of the presently continuing development of the Transcaspian Kopet Dagh and Balkhan foredeeps. This process forms the major Transcaspian seismogenic zone, possibly extending through the Caspian Sea up to the Black Sea coast. The Transcaspian seismogenic zone of a smaller size is associated with the continuing development of domelike structures of the Pribalkhano—Livanovskaya anticlinal zone in the Pribalkhanskaya depression. The generation of such earthquakes as the Kum Dagh 1983 and the Nebit Dagh (Burun) 1984 earthquakes is associated with this zone.