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Tectonic-geomorphology of the Litang fault system, SE Tibetan Plateau, and implication for regional seismic hazard

Abstract : The Litang fault system (LTFS) in the eastern Tibetan Plateau has generated several large (7.5\textgreaterM\textgreater7) historical earthquakes and has exhumed granitic peaks rising \textgreater1700 m above the mean elevation of the plateau, despite being located within a tectonic block surrounded by highly active faults. We study horizontally offset moraine crests from the Cuopu basin and a vertically offset alluvio-glacial fan from the eastern Maoya basin. We determine a left-lateral rate of 0.09 +/- 0.02 mm/yr along a slowly slipping secondary fault at Cuopu, while the main active fault at present is the normal range-front N Cuopu fault, along which we determined a left-lateral rate of 2.3 +/- 0.6 mm/yr since 173 ka. At Maoya fan, matching the vertical 12 +/- 1 m cumulative offset with the 21.7 +/- 4.2 ka fan age yields a vertical (normal) rate of 0.6 +/- 0.1 mm/yr. This rate is very similar to that recently determined at the same location using low-temperature thermochronology (0.59 +/- 0.03 mm/yr since 6.6 +/- 05 Ma). Left-lateral rates along the main faults of the LTFS range between 0.9 and 23 mm/yr at all time scales from a few years to similar to 6 Ma. The facts that the LTFS is highly segmented and that at present, the Cuopu, Maoya and South Jawa segments are mostly normal (while the Litang and Dewu segments are left-lateral/normal), could prevent the occurrence of M\textgreater7.5 destructive earthquakes along the LTFS, as is generally assumed. However, motion on the normal faults appears to be linked with motion on the strike-slip faults, potentially allowing for exceptional larger earthquakes, and implying that the area is not experiencing pure similar to NS extension but rather NW-SE left-lateral transtension. (C) 2016 Elsevier B.V. All rights reserved.
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Marie-Luce Chevalier, Philippe Hervé Leloup, Anne Replumaz, Jiawei Pan, Dongliang Liu, et al.. Tectonic-geomorphology of the Litang fault system, SE Tibetan Plateau, and implication for regional seismic hazard. Tectonophysics, 2016, 682, pp.278-292. ⟨10.1016/j.tecto.2016.05.039⟩. ⟨hal-02331126⟩



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