Seismotectonics of the Chersky Seismic Belt, eastern Sakha Republic (Yakutia) and Magadan District, Russia

Abstract. The Chersky seismic belt represents a zone of deformation between the North American and Eurasian plates in northeast Russia. The belt extends from the Laptev Sea into the Chersky Range where it splits into two branches. One branch extends to Kamchatka and the Aleutian-Kurile Junction, while the other branch extends south towards Sakhalin Island. Focal mechanisms indicate a change from extension to transpression in the northern Verkhoyansk Range and generally left-lateral transpression in the Chersky Range extending to northern Kamchatka. The few focal mechanisms on the second branch suggest right-lateral transpression. A large number of faults, sub-parallel to the seismicity and presumed to be strike-slip, are visible in satellite imagery and topographic maps and are also associated with seismically generated landslides.

These data support a model in which the Sea of Okhotsk forms the core of a separate Okhotsk microplate surrounded by diffuse boundaries on the north and west. Microseismicity in continental northeast Russia is most heavily concentrated within and between the fault systems along the northern boundary of the proposed Okhotsk plate and indicates a high level of deformation. The sense of slip on the faults (both from focal mechanisms and geology) are also generally consistent with the extrusion of the Okhotsk plate to the southeast as it is compressed between its larger neighbors. The northernmost part of the Okhotsk plate may be decoupled to some degree from the more stable central Sea of Okhotsk.