Strong Ulakhan-Chistay earthquake (Ms = 5.7) January 20, 2013 in the zone of influence Ulakhan fault system in North East Russia

Abstract

In this paper we present the results of the interpretation of seismological, geologic-structural, seismotectonic and macroseismic data obtained for the focal zone of the strong Ulakhan- Chistay earthquake (Ms = 5.7), which occurred on January 20, 2013, in the Chersky seismotectonic zone on the boundary of the Eurasian and North American lithospheric plates. The shock occurred in the zone of a large Ulakhan fault, which is visible in satellite images and can be seen in the topography between the Indigirka and Kolyma Rivers at a distance of 1,500 km. Statistics of seismic observations in the last century and at the beginning of this century show that more than 14,000 local events were noted in the zone of influence of the Ulakhan fault within the crust (~ 35 km thick) at a depth of 7–30 km. The epicentral intensity of more than ten of them reached 6–8 on the Russian scale (MSK-64). In addition to high seismicity, additional geodynamic indicators of the reactivation of the Ulakhan fault in modern times were identified — in particular, high heat flux, icing processes, paleo- and modern seismic dislocations, etc. The macro effects of this event were studied on an area of 300,000 square kilometers in three Arctic regions of Yakutia and in the south of the Magadan region; its epicenter is located by the proximity to the well-preserved paleoseismic dislocation Uryun-Takh-Takh, which arose more than a thousand years ago and is clearly visible in the search system of Google. As a result, a structural-dynamic model of the Ulakhan fault zone is proposed, explaining the occurrence of the Ulakhan-Chistay earthquake on the basis of the kinematic scheme of the Omulevsky block, which is undergoing extrusion by a collision between the Eurasian and North American lithospheric plates in Northeast Asia.