Stable rate of slip along the Karakax Valley Fault from observation of inter-glacial and post-glacial offset morphology and surface dating

Digital elevation maps obtained using TanDEM-X and Pleiades data combined with newly23 obtained surface age estimates using Cosmogenic Radionuclide (CRN) and Optically Sim24 ulated Luminescence (OSL) methods are used to quantify the slip-rate along the west25 ern section of the Altyn Tagh fault in southern Xinjiang. The reconstruction of the con26 ical shape of massive alluvial fans inferred to be from the Eemian (115±7 ka) from CRN27 dating shows consistent left-lateral offsets of 300±20 m, yielding a slip rate of 2.6±0.328 mm/yr. Successive episodes of incision have left cut terraces inset in wide canyons, 10-29 25 m below the fans’ surface. The incision was followed by the deposition of a broad ter30 race of early Holocene age, which is re-incised by modern stream channels. Near the vil31 lage of Shanxili, a 200 m-wide valley is partially dammed by a shutter ridge displaced32 by the fault. A fill terrace deposited upstream from the ridge has an OSL age of 8.8±0.633 ka. The 23±2 m offset of the riser incising the terrace indicates a minimum post-depositional34 movement on the fault, yielding a Holocene rate of 2.6±0.5 mm/yr, consistent with the35 115 ka-average slip rate. Scarp degradation analysis using mass diffusion reveals a non36 linear relationship between fault displacement and degradation coefficient along the pro37 gressively exposed fault scarp, a pattern suggesting either seismic clustering or variable38 diffusion rate since the Eemian. Together with the Gozha Co-Longmu Co fault to the39 south, the Karakax section of the Altyn Tagh Fault contributes to the eastward move40 ment of the western corner of Tibet.