Late Quaternary slip rates and Holocene paleoearthquakes of the eastern Yumu Shan fault, northeast Tibet: Implications for kinematic mechanism and seismic hazard

The Yumu Shan (YMS) fault zone at the northeastern margin of the Tibetan Plateau is characterized by actively growing fault-related folds and northeast-vergent thrusts or buried faults. This fault zone is expressed by an arc shaped fault line and can be divided into two segments: the northern and eastern YMS faults. Numerous studies indicated that the northern YMS fault is marked by reverse faulting with a left-lateral component and has undertaken two surface-rupturing events in the Holocene. But previous studies on the eastern YMS fault were conducted in the 1990s, and the limitations of dating and survey techniques led to a large uncertainty in fault slip rates and paleoseismological results. In addition, the kinematic mechanism of the arc-shaped YMS fault zone remains unknown. In this study, combining with the interpretation of high-resolution satellite imagery, real-time kinematic (RTK) GPS survey, optically stimulated luminescence (OSL) and Accelerator Mass Spectrometry (AMS) radiocarbon dating of deformed landforms and trenching, we study slip rates and paleoseismology along the eastern YMS fault. Our results show that its Late Quaternary vertical and horizontal slip rates are similar to 0.3-0.4 mm/yr and similar to 1.1 +/- 0.1 mm/yr, respectively. At its northwest tip, the fault consists of several sub-parallel branches and becomes dominantly reverse or thrusting with a vertical rate of similar to 1.1 mm/yr. Trenching data indicate that two events ruptured the eastern YMS fault occurring at 7.37-5.24 ka and 5.17-4.01 ka, respectively. The eastern YMS fault may behave synchronously or interact with the northern YMS fault. We propose that the arcuate structure under the perpendicular compression to the arch apex might illustrate the kinematic mechanism of the YMS fault zone.