Seismotectonic analysis of the Olekma-Stanovoy region, South Yakutia (paleoseismogeological aspects)

V.S.Imaev*1,2,L.P. Imaeva1,2,B.M.Kozmin2, Smekalin O.P.1,N.N.Grib3 1Institute of Earth Crust, Siberian Branch of RAS Irkutsk 664033, 2 Diamond and Precious Metals Geology Institute, Siberian Branch of RAS, Yakutsk 677007, Russia 3 Technical Institute(branch) North-Eastern Federal University,Neryungri,678960,

Accepted for publication on 30th April 2016

Geological, tectonical and seismological studies carried out in South Yakutia for more than 50 years revealed seismogenerating structures in the interaction zone of the Eurasian and Amur lithospheric plates. The structures traceable within the -Amur interfluve, between 50° and 60° N, extends eastwestward as a wide (up to 400 km) seismic band over a distance of 3000 km from Lake Baikal, through Transbaikalia, South Yakutia and Priamuria, to the Sea of Okhotsk. The zone of plate interaction is bordered on the north by the Baikal-Stanovoy seismic belt (BSB) extending eastwestward from Lake Baikal along the southern margin of the Siberian platform, through the Stanovoy highlands in Transbaikalia, the Stanovoy Range and the -Uchur plateau in South Yakutia, to the Sea of Okhotsk. The BSB combines the events of the Baikal rift zone (BRZ) in the west and the Olekma-Stanovoy zone (OSZ) in the east. During nearly the 50-year period of instrumental observations, more than 150 thousand events with M ≥2 were reported from the BRZ and over 40 thousand from the OSZ. The southern boundary of the plate interaction zone is marked by an epicentral cluster extending eastwestward from Northern Mongolia, through East Transbaikalia along the Tukuringra- Soktakhan-Dzhagdy Ranges in Priamuria to the Sea of Okhotsk. Within this boundary, the Tukuringra-Dzhagdy seismic zone (TDZ) is most active. It is located 200 km to the south of the OSZ and, extends parallel to it between 54° and 55° N to the east of 120° E. Some eight thousand seismic events were detected in the zone over the 50-year period. According to the focal mechanism solutions, motions in the earthquake foci within the OSZ and TDZ are of left-lateral strike- slip, thrust and reverse fault nature (Imaev et al., 2000; Imaeva et al., 2007; 2008; Mackey et al., 2003). The NS-trending Temulyakite-Dzheltula seismic band divides the zone of interaction of the Eurasian and Amur lithospheric plates into two blocks – Transbaikalian – from Lake Baikal up to the Olekma River and the Aldan-Stanovoy – from Olekma to the Sea of Okhotsk (Imaeva et al., 2007; 2008). The described seismotectonic setting the relationship between the regional faults and the foci of associated strong seismic events, as well as the present-day tectonic stress fields are be studied in detail based on the focal mechanism solutions of earthquakes and geological and structural observation datas, as well as the data on the system of plates and blocks in Pribaikalia, Priamuria and South Yakutia. This study was supported by grant Russian National Foundation (RNF 15-17-20000) Keywords: active faults,earthquakes, pfleoseismicity,tectonic stress fields,seosmotectonics.