The Western Kunlun mountain range is a slowly converging intracontinental orogen where deformation rates are too low to be properly quantified from geodetic techniques. This region has recorded little seismicity, but the recent July 2015 (Mw 6.4) Pishan earthquake shows that this mountain range remains seismic. To quantify the rate of active deformation and the potential for major earthquakes in this region, we combine a structural and quantitative morphological analysis of the Yecheng–Pishan fold, along the topographic mountain front in the epicentral area. Using a seismic profile, we derive a structural cross section in which we identify the fault that broke during the Pishan earthquake, an 8–12 km deep blind ramp beneath the Yecheng–Pishan fold. Combining satellite images and DEMs, we achieve a detailed morphological analysis of the Yecheng–Pishan fold, where we find nine levels of incised fluvial terraces and alluvial fans. From their incision pattern and using age constraints retrieved on some of these terraces from field sampling, we quantify the slip rate on the underlying blind ramp to 0.5 to 2.5 mm/yr, with a most probable long‐term value of 2 to 2.5 mm/yr. The evolution of the Yecheng–Pishan fold is proposed by combining all structural, morphological, and chronological observations. Finally, we compare the seismotectonic context of the Western Kunlun to what has been proposed for the Himalayas of Central Nepal. This allows for discussing the possibility of M ≥ 8 earthquakes if the whole decollement across the southern Tarim Basin is seismically locked and ruptures in one single event.
Kinematic constraints on the Cenozoic deformation along the northwestern edge of the Tibetan Plateau remain limited. Combining surface geological data and seismic profiles, we document the structural geometry and kinematics of the large‐scale east‐west striking Hotan anticline, along the foothills of the Western Kunlun Range. Four new balanced cross sections are constructed, and the temporal evolution of deformation is deciphered from the exceptionally well‐imaged growth strata at the front of the fold. This anticline results from a broad fault‐bend fold, subsequently deformed by a footwall duplex. The total shortening across the whole structure is relatively constant along strike, from ∼40 to ∼35 km. However, the shortening accommodated by the duplex varies laterally from ∼50–40% to 0% of the total shortening. Two distinct successive patterns of growth strata are recognized and are interpreted to be representative of deformation on the ramp anticline, followed by deformation on the duplex. The onset of deformation initiated by ∼16 Ma. Deformation of the underlying duplex began at ∼12 Ma to the west and subsequently propagated eastward. From these results, we determine a shortening rate of ∼5 mm/yr from ∼16 to ∼8–9 Ma across the Hotan thrust system, followed by a significant decrease in shortening rate, possibly down to <0.5 mm/yr. We explore the significance of this deceleration of deformation at the scale of the Western Kunlun foothills and at a broader regional scale as it may point to a regional kinematic reorganization by the late Miocene.
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