Limit on slip rate and timing of recent seismic ground-ruptures on the Jinghong fault, SE of the eastern Himalayan syntaxis

Abstract

Quantifying slip rates and earthquake occurrence of active faults on the Shan Plateau, southeast of the eastern Himalayan syntaxis, is critical to assessing the seismic hazard and understanding the kinematics and geodynamics of this region. Most previous estimates of slip rates are averaged over either many millions of years using offset geological markers or decades using GPS. Well-constrained millennial slip rates of these faults remain sparse and constraints on recurrence rates of damaging earthquakes exist only for a few faults. Here we investigate the millennial slip rate and timing of recent earthquakes on the Jinghong fault, one of the geomorphically most significant sinistral-slip faults on the central Shan Plateau. We map and reconstruct fault offset (18 ± 5 m) of alluvial fan features at Manpa on the central Jinghong fault, using a 0.1 m-resolution digital surface model obtained from an unmanned aerial vehicle survey. We establish a slip rate, ≤2.5 ± 0.7 mm/yr over the past ~7000 years, using pit-exposed stratigraphy. This millennial slip rate is consistent with rates averaged over both decadal and million-year timescales. Excavations at three sites near the town of Gelanghe on the northeastern Jinghong fault demonstrate 1) that the last seismic ground-rupture occurred between 482 and 889 cal yr BP, most likely in the narrower window 824–767 cal yr BP, if the lack of large earthquakes in the historical earthquake record is reliable, and 2) that multiple fault ruptures have occurred since ~3618 cal yr BP. Combining this finding with a lack of large earthquakes in the ~800-year-long Chinese historic record in this region, we suggest an average recurrence interval of seismic ground-ruptures on the order of ~1000 years. This recurrence interval is consistent with the slip rate of the Jinghong fault and the size and earthquake frequency on other sinistral faults on the Shan Plateau.