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Bishkek, Kyrgyzstan

Campbell G.E.,University of Cambridge | Walker R.T.,University of Oxford | Abdrakhmatov K.,Kyrgyz Institute of Seismology | Jackson J.,University of Cambridge | And 4 more authors.
Journal of Geophysical Research B: Solid Earth | Year: 2015

The Lepsy fault of the northern Tien Shan, SE Kazakhstan, extends E-W 120 km from the high mountains of the Dzhungarian Ala-tau, a subrange of the northern Tien Shan, into the low-lying Kazakh platform. It is an example of an active structure that connects a more rapidly deforming mountain region with an apparently stable continental region and follows a known Palaeozoic structure. Field-based and satellite observations reveal an ∼10 m vertical offset exceptionally preserved along the entire length of the fault. Geomorphic analysis and age control from radiocarbon and optically stimulated luminescence dating methods indicate that the scarp formed in the Holocene and was generated by at least two substantial earthquakes. The most recent event, dated to sometime after ∼400 years B.P., is likely to have ruptured the entire ∼120 km fault length in a Mw 7.5-8.2 earthquake. The Lepsy fault kinematics were characterized using digital elevation models and high-resolution satellite imagery, which indicate that the predominant sense of motion is reverse right lateral with a fault strike, dip, and slip vector azimuth of ∼110°, 50°S, and 317-343°, respectively, which is consistent with predominant N-S shortening related to the India-Eurasia collision. In light of these observations, and because the activity of the Lepsy fault would have been hard to ascertain if it had not ruptured in the recent past, we note that the absence of known active faults within low-relief and low strain rate continental interiors does not always imply an absence of seismic hazard. ©2015. The Authors.

Campbell G.E.,University of Cambridge | Walker R.T.,University of Oxford | Abdrakhmatov K.,Kyrgyz Institute of Seismology | Schwenninger J.,University of Oxford | And 3 more authors.
Journal of Geophysical Research: Solid Earth | Year: 2013

The Dzhungarian strike-slip fault of Central Asia is one of a series of long, NW-SE right-lateral strike-slip faults that are characteristic of the northern Tien Shan region and extends over 300 km from the high mountains into the Kazakh Platform. Our field-based and satellite observations reveal that the Dzhungarian fault can be characterized by three 100 km long sections based on variation in strike direction. Through morphological analysis of offset streams and alluvial fans, and through optically stimulated luminescence dating, we find that the Dzhungarian fault has a minimum average late Quaternary slip rate of 2.2 ± 0.8 mm/yr and accommodates N-S shortening related to the India-Eurasia collision. This shortening may also be partly accommodated by counterclockwise rotation about a vertical axis. Evidence for a possible paleo-earthquake rupture indicates that earthquakes up to at least Mw 7 can be associated with just the partitioned component of reverse slip on segments of the central section of the fault up to 30 km long. An event rupturing longer sections of the Dzhungarian fault has the potential to generate greater magnitude earthquakes (Mw 8); however, long time periods (e.g., thousands of years) are expected in order to accumulate enough strain to generate such earthquakes. Key Points The Dzhungarian fault is an active strike-slip of the N. Tien Shan, Central Asia It accommodates a minimum of 2.2 +/- 0.8 mm/yr of right-lateral slip The Dzhungarian fault has the potential to generate large (> Mw 7) earthquakes ©2013. American Geophysical Union. All Rights Reserved.

Sanhueza-Pino K.,University of Munster | Korup O.,University of Potsdam | Hetzel R.,University of Munster | Munack H.,University of Potsdam | And 4 more authors.
Quaternary Research | Year: 2011

Numerous large landslide deposits occur in the Tien Shan, a tectonically active intraplate orogen in Central Asia. Yet their significance in Quaternary landscape evolution and natural hazard assessment remains unresolved due to the lack of "absolute" age constraints. Here we present the first 10Be exposure ages for three prominent (>10 7m 3) bedrock landslides that blocked major rivers and formed lakes, two of which subsequently breached, in the northern Kyrgyz Tien Shan. Three 10Be ages reveal that one landslide in the Alamyedin River occurred at 11-15ka, which is consistent with two 14C ages of gastropod shells from reworked loess capping the landslide. One large landslide in Aksu River is among the oldest documented in semi-arid continental interiors, with a 10Be age of 63-67ka. The Ukok River landslide deposit(s) yielded variable 10Be ages, which may result from multiple landslides, and inheritance of 10Be. Two 10Be ages of 8.2 and 5.9ka suggest that one major landslide occurred in the early to mid-Holocene, followed by at least one other event between 1.5 and 0.4ka. Judging from the regional glacial chronology, all three landslides have occurred between major regional glacial advances. Whereas Alamyedin and Ukok can be considered as postglacial in this context, Aksu is of interglacial age. None of the landslide deposits show traces of glacial erosion, hence their locations and 10Be ages mark maximum extents and minimum ages of glacial advances, respectively. Using toe-to-headwall altitude ratios of 0.4-0.5, we reconstruct minimum equilibrium-line altitudes that exceed previous estimates by as much as 400m along the moister northern fringe of the Tien Shan. Our data show that deposits from large landslides can provide valuable spatio-temporal constraints for glacial advances in landscapes where moraines and glacial deposits have low preservation potential. © 2011 University of Washington.

Havenith H.-B.,University of Liege | Abdrakhmatov K.,Kyrgyz Institute of Seismology | Torgoev I.,Institute of Geomechanics and Development of Subsoil | Ischuk A.,Institute of Earthquake Engineering and Seismology | And 3 more authors.
Landslide Science and Practice: Risk Assessment, Management and Mitigation | Year: 2013

This paper presents an overview of seismic and mass movement hazards affecting major Hydropower-plants (HPP) and ongoing dam projects in the mountain regions of Central Asia. HPP cascades are located along the Naryn River in the Kyrgyz Republic and the Vakhsh-Surkhob valley fault zone in Tajikistan. The latter region hosting the presently and future tallest man-made dams of the world is very prone to earthquakes and various types of slope instabilities. The Naryn Valley hosting several dam sites is marked by the presence of ancient rockslides and a dense network of seismically active faults. In December 2009, Kyrgyz, Russian, Slovak and Belgian teams have monitored seismic ground motions and displacements induced by the blasting of a slope on the Kambarata 2 site producing a 35 m-high blockage on the Naryn River. This work is part of a NATO Science for Peace and Security project on landslide dam hazards in the Tien Shan. © Springer-Verlag Berlin Heidelberg 2013.

Rosenwinkel S.,University of Potsdam | Korup O.,University of Potsdam | Landgraf A.,University of Potsdam | Dzhumabaeva A.,Kyrgyz Institute of Seismology
Quaternary Science Reviews | Year: 2015

Lichenometry is a straightforward and inexpensive method for dating Holocene rock surfaces. The rationale is that the diameter of the largest lichen scales with the age of the originally fresh rock surface that it colonised. The success of the method depends on finding the largest lichen diameters, a suitable lichen-growth model, and a robust calibration curve. Recent critique of the method motivates us to revisit the accuracy and uncertainties of lichenometry. Specifically, we test how well lichenometry is capable of resolving the ages of different lobes of large active rock glaciers in the Kyrgyz Tien Shan. We use a bootstrapped quantile regression to calibrate local growth curves of Xanthoria elegans, Aspicilia tianshanica, and Rhizocarpon geographicum, and report a nonlinear decrease in dating accuracy with increasing lichen diameter. A Bayesian type of an analysis of variance demonstrates that our calibration allows discriminating credibly between rock-glacier lobes of different ages despite the uncertainties tied to sample size and correctly identifying the largest lichen thalli. Our results also show that calibration error grows with lichen size, so that the separability of rock-glacier lobes of different ages decreases, while the tendency to assign coeval ages increases. The abundant young (<200 yr) specimen of fast-growing X. elegans are in contrast with the fewer, slow-growing, but older (200-1500 yr) R. geographicum and A. tianshanica, and record either a regional reactivation of lobes in the past 200 years, or simply a censoring effect of lichen mortality during early phases of colonisation. The high variance of lichen sizes captures the activity of rock-glacier lobes, which is difficult to explain by regional climatic cooling or earthquake triggers alone. Therefore, we caution against inferring palaeoclimatic conditions from the topographic position of rock-glacier lobes. We conclude that lichenometry works better as a tool for establishing a relative, rather than an absolute, chronology of rock-glacier lobes in the northern Tien Shan. © 2015 Elsevier Ltd.

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