Long, Regular Return of Four Large Earthquakes on Qilian Shan's Minle-Damaying Frontal Thrust (NE Tibet): Partial Clustering With Great Events on the Leng Long Ling Fault?

The exact geometry and rupture behavior of the Minle-Damaying Thrust (MDT), along NE Tibet's Qilian Shan's mountain front, remain unclear. Based on a new similar to 45 km long, similar to 2.5 km wide, and 0.5 m resolution Unmanned Aerial Vehicle survey of the thrust's eastern part, we accurately map its surface trace in order to identify and quantify the sizes of large post-glacial earthquakes. Our geomorphic measurements (72 vertical offsets [VOs] ranging from 1.2 to 13.8 m) validated by fieldwork, reveal four distinct peak throw clusters (similar to 2.2, 5.4, 8.3, 11.6 m) along the slightly stepping, frontal strands of the foreland-propagating thrust trace. Shallow thrust dip-angles constrained by the three-point method at five sites range from similar to 32 degrees to 43 degrees. Anchoring our 72 throw measurements to previous dating results and paleo-seismological trench logs at the Xie river site, implies that the MDT's eastern segment broke regularly with similar to 2.9(+0.6)/(-0.8) m of nearly characteristic average VO (similar to 4.9 m of slip) to produce Mw similar to 7.0-7.4 earthquakes, with a return time of similar to 3.6(+0.8)/(-1.0) ka since similar to 12.7 ka. Paleo-seismological results suggest that the occurrence of thrust earthquakes on the MDT may be coupled with that of large strike-slip events, similar to the 1927, Mw similar to 8, Gulang earthquake on the neighboring (similar to 18 km SW) Leng Long Ling segment of the Haiyuan Fault. That co-seismic slip on the latter might control similar to coeval slip along the sub-parallel MDT may reflect a rupture behavior dictated by their partitioning/bifurcation at similar to 20 km depth, close to their adjacent, restraining, left-stepping bends.

Automated summary

Using an Unmanned Aerial Vehicle survey, the surface trace of the Minle-Damaying Thrust (MDT) in NE Tibet's Qilian Shan's mountain front is accurately mapped, revealing its rupture behavior and geometry. The study shows that the eastern segment of the MDT regularly ruptures with an average vertical offset of around 2.9 meters, producing large earthquakes with magnitudes of 7.0-7.4.