Seismicity and Crustal Structure of the Southern Crimea and Adjacent Northern Black Sea from Local Seismic Tomography

Abstract

The Main Caucasus Thrust, which marks the southern boundary of the Greater Caucasus orogen can be traced westward along the northern margin of the Black Sea and southern Crimea and coincides with a zone of seismicity called the Crimea Seismic Zone (CSZ). The CSZ is characterized by earthquakes of M = 3–5 with foci in the crust and uppermost mantle with abundant weak seismicity (M ≤ 3). Weak seismicity was used to recover the velocity structure of the crust of southern Crimea Peninsula and adjacent northern Black Sea employing local seismic tomographic techniques. Events were recorded during 1970–2013 by nine stations on the Crimea Peninsula and by one station (Anapa) on the Caucasus coast of the Black Sea. Data for the tomographic inversion were relocated for the P- and S-wave arrivals at all permanent stations of CSZ. The new local tomographic study documents significant P- and S-wave velocity heterogeneities in the depth range 10–30 km. Stable solutions have been obtained for depths of 15, 20 and 25 km. A distinctive feature of the crust of southern Crimea is its clear division on two domains: a western domain (Crimean Mountains) and an eastern one (Kerch-Taman zone). They are separated by a linear low-velocity zone of ~N-S strike (in the area between Sudak and Feodosiya) interpreted as a zone of crustal weakness that has been repeatedly reactivated. Interpretation of velocity anomalies suggests a complex 3-D crustal geometry that involved a change of underthrusting polarity in the western Crimea Mountains crust compared to eastern Crimea.