Active Tectonics Around Almaty and along the Zailisky Alatau Rangefront. Issue 10 (25th October 2017)

• Record Type: Journal Article
• Authors: Grützner, C.; Walker, R. T.; Abdrakhmatov, K. E.; Mukambaev, A.; Elliott, A. J.; Elliott, J. R.
• Is Part Of: Tectonics. Volume 36:Issue 10(2017)
• Page Start: 2192
• Page End: 2226
• Publication Date: 2017-10-25
• Subjects: Tien Shan -- Zailisky Alatau -- active tectonics -- tectonic geomorphology -- earthquakes and faulting; Geology, Structural -- Periodicals; 551.8
• DOI: 10.1002/2017TC004657
• Languages: English
• ISSNs: 0278-7407

Abstract

Abstract: The Zailisky Alatau is a >250 km long mountain range in Southern Kazakhstan. Its northern rangefront around the major city of Almaty has more than 4 km topographic relief, yet in contrast to other large mountain fronts in the Tien Shan, little is known about its Late Quaternary tectonic activity despite several destructive earthquakes in the historical record. We analyze the tectonic geomorphology of the rangefront fault using field observations, differential GPS measurements of fault scarps, historical and recent satellite imagery, meter‐scale topography derived from stereo satellite images, and decimeter‐scale elevation models from unmanned aerial vehicle surveys. Fault scarps ranging in height from ~2 m to >20 m in alluvial fans indicate that surface rupturing earthquakes occurred along the rangefront fault since the Last Glacial Maximum. Minimum estimated magnitudes for those earthquakes are M 6.8–7. Radiocarbon dating results from charcoal layers in uplifted river terraces indicate a Holocene slip rate of ~1.2–2.2 mm/a. We find additional evidence for active tectonic deformation all along the Almaty rangefront, basinward in the Kazakh platform, and in the interior of the Zailisky mountain range. Our data indicate that the seismic hazard faced by Almaty comes from a variety of sources, and we emphasize the problems related to urban growth into the loess‐covered foothills and secondary earthquake effects. With our structural and geochronologic framework, we present a schematic evolution of the Almaty rangefront that may be applicable to similar settings of tectonic shortening in the mountain ranges of Central Asia. Key Points: Post Last Glacial Maximum tectonic activity along the Almaty rangefront is expressed in fault scarps in alluvial fans, folding, uplifted abandoned river terraces, and backthrusts Active deformation is laterally distributed, affecting the rangefront, the interior of the mountains, and the foreland The Holocene slip rate of the rangefront fault is ~1.2–2.2 mm/a in the eastern section