UNIFORM LATE QUATERNARY SLIP RATE ALONG THE JINGHONG FAULT, SE OF THE EASTERN HIMALAYAN SYNTAXIS

Quantifying slip rates of active faults in the broad region southeast of the eastern Himalayan syntaxis and their spatio-temporal variations is critical to assessing regional seismic hazard and understanding regional deformation field and geodynamic processes. To date, little is known about the rate variations for most faults in this region. Here we chose one of primary sinistral faults on the Shan Plateau, the Jinghong fault, to constrain its slip behaviour in time and space since the Late Pleistocene. We targeted two field sites near the town of Gelanghe along the northeastern Jinghong fault, and mapped geomorphic surfaces and fault offsets by field investigation and high-resolution digital topography, including 1) 0.5 m-resolution digital elevation model produced by Unmanned Aerial Vehicle – based Light Detection and Ranging (UAV-LiDAR) and, 2) AW3D 5 m-resolution digital surface elevation model produced by the Advanced Land Observing Satellite imagery. We used optically stimulated luminescence (OSL) dating of the offset-related sediments to determine the age bounds of fault offsets. At the Yumu site, a granite strath terrace was displaced sinistrally by 90±10 m, the fluvial conglomerates immediately capped on the strath (possibly after the onset of this fault offset) have an OSL age of ~21.7±1.4 ka, thus providing a slip rate of <3.5 mm/yr. At the Nange fan site, the fault displaced the edge of an older alluvial fan by 70±10 m and later capped a younger fan. The OSL ages for the older and younger fan sediments are >92 ka and ~19.8±1.2 ka, respectively, thus constraining the slip rate at this site to 0.7-4.3 mm/yr. Considering these two sites are only ~1 km apart, we constrain the slip rate to 0.7-3.5 mm/yr, or 2.1±1.4 mm/yr, consistent with the approximate geodetic rate (<2.4 mm/yr) and the 500-1000 years of recurrence interval of damaging earthquakes along this fault segment (Shi et al., Tectonophysics). Comparing this result with our previous slip rate of <2.5±0.7 mm/yr on the central Jinghong fault, we suggest this fault exhibits a uniform slip behavior since the Late Pleistocene.