LATE QUATERNARY SLIP RATE OF THE MIDDLE SEGMENT OF THE GANZI-YUSHU FAULT ZONE CONSTRAINED BY NUMERICAL (CRN AND OSL) DATING OF OFFSET MORAINE AND TERRACES

Slip rate along major active faults is a sign of the intensity of fault activities and a basis for understanding earthquake recurrence-time. The Ganzi-Yushu Fault Zone (GZFZ) is a large left lateral strike-slip fault lying between the Qiangtang and Bayan Har-Songpan blocks and also an important part of the major boundary fault in the southeastern Tibetan Plateau. Due to the lack of robust numerical ages of displaced landforms/sediments along the GZFZ, the understanding of the slip rates and the nature is still an open question. In this study we investigated a glacial lateral moraine (Yingpu Moraine) and glaciofluvial terraces (Wangqing and Wuming Terraces) which have been displaced (both vertically and horizontally) by the GZFZ. The offset landforms were surveyed using RTK GPS and dated with cosmogenic ¹⁰Be and optical stimulated luminescence (OSL) dating methods. The offset moraine was dated to ~17 ka (8 ¹⁰Be ages) and has mean vertical and horizontal slip rate of ~2 mm/a and 4.1 mm/a, respectively. The Wangqing and Wuming Terrace has a mean OSL age of ~19 ka (n=2) ,the vertical slip rate is 0.7 mm/a and horizontal slip rate is 4 mm/a. Estimation of slip rate would provide data for future research on seismotectonic of strike-slip faults and tectonic evolution of the Tibetan plateau.