HR: 16:20h
AN: T14C-02    [Abstracts]
TI: Surface rupture along the Chon Aksu and Aksu (eastern) segments of the 1911 Kebin (Chon-Kemin) earthquake, Tien Shan, Kyrgyzstan
AU: * Arrowsmith, J R
EM: ramon.arrowsmith@asu.edu
AF: Arizona State University, Department of Geological Sciences, Tempe, AZ 85287 United States
AU: Crosby, C J
EM: chris.crosby@asu.edu
AF: Arizona State University, Department of Geological Sciences, Tempe, AZ 85287 United States
AU: Korjenkov, A M
EM: akorjen@elcat.kg
AF: Kyrgyz Institute of Seismology NAS KR, Asanbay 52/1, Bishkek, 720060 Kyrgyzstan
AU: Mamyrov, E
EM: akorjen@elcat.kg
AF: Kyrgyz Institute of Seismology NAS KR, Asanbay 52/1, Bishkek, 720060 Kyrgyzstan
AU: Povolotskaya, I E
EM: pie_293174@rambler.ru
AF: Kyrgyz Institute of Seismology NAS KR, Asanbay 52/1, Bishkek, 720060 Kyrgyzstan
AB: The 1911 Ms 8.2 Kebin (Chon-Kemin) earthquake is one of the largest intraplate reverse-faulting events to occur historically. It ruptured a 200 km E-W trending zone in the northern Tien Shan. Description of the characteristics of major historic earthquakes, such as the Chon-Kemin event, provide data on the primary deformation and its initial geomorphic degradation, thus informing paleoseismological investigations. Trace geometry and offset distribution are key parameters for the interpretation of the seismotectonic setting and mechanical interaction with other regional structures. The Chon-Kemin earthquake's relationship to other large regional earthquakes, notably the 1887 Ms 7.3 Verny and 1889 Ms 8.3 Chilik events, indicates a strong interaction between structures in this portion of the Tien Shan. We reconnoitered most of the Chon-Kemin rupture belt and associated mass movements and conclude that many of the 1911 features are still well preserved. We emphasized mapping and description of the easternmost 50 km of the rupture, along the Aksu (easternmost) and Chon-Aksu segments. Moving from east to west, 1-3 m high fault scarps and warped Holocene terraces discontinuously cut the piedmonts north and northeast of the town of Anan'evo. The rupture closely follows the mountain front and enters the range just below the Anan'evo landslide (formed in the earthquake). Scarp heights are 2-4 m. West of the Tegermenty River, the left-stepping rupture is continuous and consists of sub parallel strands in places. Between the Sutubulak and the Aksu River crossing, some of the tallest scarps are present, with heights of 6 - 10 m. The generally north-dipping fault zone has low south dips in the near surface as the thrust has driven the hanging wall over the south-sloping piedmont. This change in dip is likely responsible for the formation of E-W extensional faults in the hanging wall. Given the shallow fault dips and tall scarps in this area, 1911 displacement is probably $>$ 10 m. The Aksu segment ends in a 5 km wide left step through the Kok Bel Pass into the Chon Asku Valley. Fault scarps are 2-4 m high and a small corral, offset in 1911, shows no evidence for strike-slip displacement. In the Kok Bel Pass, the hanging wall (northwestern) is crossed by numerous clear and straight fault scarps trending mostly NE. The eastern 9 km of the Chon Aksu segment preserves the most spectacular tectonic landforms from the 1911 rupture. Scarps are typically uphill-facing and 6-8 m high in this reach with some domal uplifts deforming Pleistocene fluvial terraces. Two tectonically dammed lakes were formed by the 1911 earthquake. In addition, the Chon Aksu river was offset with the upstream side uplifted about 6 m. In the upper Chon Aksu Valley, the rupture is not well expressed, because of vigourous fluvial, periglacial and glacial activity. Notable fractures on ridgetops on the south side of the valley across from the Kulugan Tash rockfall are well preserved, but their formation as primary ground rupture or shaking induced settling is ambiguous. For 5 km west of the Kulugan Tash, no landforms were unambiguously attributable to ground rupture. Together with 1911 earthquake features in the study area, we also observed scarps and mass movements belonging to paleoseismic catastrophes. They indicate recurrence of major earthquakes along this structure during the Holocene and late Pleistocene.
DE: 7221 Paleoseismology
DE: 8107 Continental neotectonics
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting