TECTONIC POSITION AND GEOLOGICAL MANIFESTATIONS OF THE 2006 OL’UTOR EARTHQUAKE
IN NORTH KAMCHATKA

ROGOZHIN E.A., OVSYUCHENKO A.N.,
NOVIKOV S.S., MARAKHANOV A.V.

 Institute of Physics of the Earth, RAS, 10 B.Gruzinskaya, Moscow, 123995. E-mail: eurog@ifz.ru


The results of the field seismotectonic study for the epicentral zone of the major earthquake (M = 7.8) in the North Kamchatka (Koriak District) are presented. The primary and secondary surface ruptures were discovered. On the Earth’s surface the outcrop of the seismic source as a complicated system of seismic faults with a total length up to 140 km was found and mapped in detailed scale. The seismic fault system is represented by three extensive echelon segments of NE orientation being about 75, 40 and 16 km long and many other short faults. General strike of the faults system coincides with the orientation of the Koriak highland ridges. Kinematics of the offset is rather different on the three long segments of the seismic fault. The longest NE segment is the thrust of SE wing in combined with dextral strike-slip. Maximum vertical amplitude of the offset is 3 m and horizontal one - 1.5 m. The middle segment of the seismic fault is an almost pure right-lateral strike-slip with maximum offset up to 2 m. The most southwestern faults system’s fragment has demonstrated the left-lateral strike-slip with the offset up to 1.3-1.8 m. Vibration fissures, griffons, marks of liquefaction, landslides and rockfalls were found and mapped as secondary surface breaches. The paleoseismic ruptures were studied and documented. The samples of paleosoil were extracted, radiocarbon dating was fulfilled and the age of the paleo-earthquakes was determined. Four prehistoric earthquakes occurred in the same source in the time periods 7000-6000, 3700-3500, 2500-2000 and 1500-1000 years ago. So, the recurrence interval between four last events (including the 2006 Ol’utor seismic shock) is about 1000 years. The seismic source of the earthquake was situated on the border of the North-American and the Bering-Sea lithosphere plates and demonstrated the inner structure and recent kinematics of the border zone on the extensive segment. The seismic activation of the plate’s border testifies to the present day geological activity of the zone of lithosphere plate’s relations. The collected data allow to draw up the image of the seismic source structure and its tectonic position on the active continental margin of Asia.