Surface rupture of the 1911 Kebin (Chon-Kemin) earthquake, Northern Tien Shan, Kyrgyzstan
Abstract
The 1911 Ms 8.2 Kebin (Chon-Kemin) earthquake in the Northern Tien Shan, Kyrgyzstan is one of the largest historic intraplate reverse-faulting events. Documentation of slip distribution and fault geometry for major historic earthquakes, such as the Chon-Kemin event, provide important data on their source physics and seismotectonics. These data also provide insight into mechanical interaction with other large regional earthquakes, notably the 1887 Ms 7.3 Verny and 1889 Ms 8.3 Chilik events. Through detailed aerial photo mapping, examination of historic data (Bogdonovich et al., 1914), and two seasons of fieldwork, we mapped the entire 200 km of the1911 rupture and associated off-fault deformation and mass movements at > 1:50,000. At the 1911 events western end, the south dipping Djel Aryk section closely follows the range front at the southern edge of the Djel Aryk Valley. Mapping by Bogdonovich et al. indicates 1.5 km of rupture west of the Chu River in 1911 but 10-20 m high fault scarps further west in the Djel Aryk Valley indicate late Pleistocene paleoseismic activity. The Lower Chon-Kemin section stretches from the Chon-Kemin gorge to Chundi-Su. The fault dips steeply south and offset landforms indicate a left-lateral slip component. Vertical 1911 displacements are 1-3 m. Most of this portion of the 1911 rupture is located 500-1500 m above the Chon-Kemin Valley on the northern flank of the Kungei-Alatau Range. Bogdonovich et al. do not report 1911 rupture between Dyure River and Chundi-Su despite clear 10-30 m tall scarps offsetting Holocene landforms. The lack of mapped ground rupture in this area in 1911 suggests either a failure of the Bogdonovich team to reach this section of fault or that the earthquake failed to rupture here, despite clearly having done so prehistorically. The Upper Chon-Kemin section comprises steeply dipping to vertical discontinuous fractures located on steep slopes above the valley floor. Bogdonovich et al. report discontinuous rupture for this section with more continuous rupture near the head of the Chon-Kemin Valley. Most of these features have not been preserved because of vigorous fluvial and periglacial activity. A 10 km right step separates the Upper Chon-Kemin section from the Chon Aksu section to the east. The eastern 9 km of the Chon Aksu section preserves the most spectacular tectonic landforms from the 1911 rupture, including 6-8 m uphill-facing scarps and a pair of tectonically dammed lakes. The Chon Aksu River channel was also offset vertically 6 m. In the upper Chon Aksu Valley, the rupture is not well expressed except for the western most 1 km, below the Chon Aksu Pass, where 1911 slip is 4-5 m. The eastern end of the Chon Aksu section is marked by a 5 km wide left step through the Kok Bel Pass into the Aksu Valley. Fault scarps along the Aksu section are 2-4 m with scarps between the Sutubulak and the Aksu River reaching 6-10 m. Given the shallow fault dips and tall scarps in this area, 1911 displacement is likely > 10 m. The lack of significant ground displacement in the center of the rupture, on the Upper Chon-Kemin and eastern portion of the Lower Chon-Kemin sections, suggests the earthquake occurred as slip along two discrete, but interacting, fault patches with the majority of seismic moment released on the Aksu and Chon Aksu segments and a lesser amount released on the Lower Chon-Kemin and Djel Aryk sections. Results from this mapping will enable a detailed estimate of the moment magnitude for the Chon-Kemin event.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2005
- Bibcode:
- 2005AGUFM.T51F..05A
- Keywords:
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- 7215 Earthquake source observations (1240);
- 8036 Paleoseismology (7221);
- 8107 Continental neotectonics (8002);
- 8108 Continental tectonics: compressional;
- 8175 Tectonics and landscape evolution