FAULT SCARPS AND PREHISTORIC EARTHQUAKES IN THE TUNKA FAULT (southwestern Baikal region)
A.V. Chipizubov, O.P. Smekalin, and R.M. Semenov
Institute of the Earth's Crust, Siberian Branch of the RAS, 128 ul. Lermontova, Irkutsk, 664033, Russia
Keywords: Fault scarp, prehistoric earthquake, recurrence time
Pages: 561-574
Subsection: GEOPHYSICS
Abstract
Decade-long paleoseismic trenching (30 trenches) across the Arshan and Tory fault scarps in the southwestern end of the Baikal basin furnished new details of seismic rupture and highlighted the geometry of different segments of the Tunka fault. It is mostly a reverse-oblique fault within its W-E part and a normal fault in NE-trending segments. The estimated Holocene left-lateral strike-slip offset is 3.5-8 m in single events, 12-16 m for single- or multiple-event displacement, and up to 22-35 m in two and more events. Trenching revealed six large prehistoric earthquakes with their ages bracketed between 1315 and 1742 ( M  7.3), 2464-2809 ( M 7.4), 5257-5907 ( M 7.2), 7091-7385 ( M 7.3), 9214-9902 ( M 8), and 10386-11187 ( M 8) years BP. Rupture during the 9-10 Ka event may have reactivated the Tunka and Main Sayan faults along 100 km in total. |
