Late Quaternary right-lateral displacement along active faults in the Yanqi Basin, southeastern Tian Shan, northwest China

Abstract

Late Quaternary right-lateral displacement and slip rates have been determined along WNW–ESE-trending active faults in the intermontane Yanqi Basin on the southeastern flank of the Chinese Tian Shan. Detailed analyses of satellite images and field investigation have revealed that the active Kaidu River fault zone on the southern margin of the basin is a strike–slip fault zone. Drainage systems incising late Pleistocene–Holocene alluvial fans record between 3 and 250 m dextral offsets and show progressive displacement along the fault zone. Fault scarps developed in the alluvial fans range in height from 1 to 25 m and alternate along the strike of the fault zone from northeast to southwest facing in a left-stepping en echelon pattern. Based on the offset of stream channels, 14C dates of alluvial deposits, and fabrics within fault rocks, we infer that (1) the average right-lateral slip rate is about 8 mm/year, with a vertical component of 1 mm/year, (2) the offset produced by individual seismic faulting event is typically 3–7 m, (3) the average recurrence interval of large seismic events ( M>7) is ca. 500 years, and (4) the most recent movement occurred during the past 2.5 ky in the Kaidu River fault zone. These strike–slip faults represent partitioning of horizontal slip within an otherwise thrust dominated orogen related to the India–Eurasia collision within the Tian Shan during late Quaternary.