Determination of mean recurrence interval of large earthquakes on the Garzê-Yushu Fault (Dengke Segment) on the eastern margin of the Qinghai–Tibetan Plateau

The Garzê-Yushu Fault is a large left-lateral shear zone in the margin of the Tibetan Plateau. It is part of the slip fault system through which the upper crust material on the margin of the Tibetan Plateau moves eastward. At Xiala Village, Luoxu Town, Shiqu County, Sichuan Province, the Garzê-Yushu Fault cuts through the front edge of the alluvial fan, resulting in fault scarps with heights of 0.2–3.7 m. Some fissures and pressure ridges caused by the Dengke AD 1896 earthquake can be found here. The main tributary river and some gullies on the alluvial fan were also left-laterally displaced. Based on active tectonic geomorphologic surveys, detailed topographic mapping, four trench excavations, and test results from radiocarbon (14C) dating and optically stimulated luminescence (OSL), the following conclusions were drawn in this paper. The trenches uncovered five paleoseismic events in the past 5000 BP, including three paleoearthquake events since AD 1100 ± 70, occurring in AD 1100 ± 70, AD 1550 ± 100, and AD 1896. The latest three paleoearthquakes led to an accumulated 8.7 ± 0.5 m sinistral dislocation with a recurrence interval of approximately 400 y. This is consistent with the quasi-periodic earthquake recurrence behavior model.