Ⓔ Historical (Yuan Dynasty) Earthquake on the North Danghe Nanshan Thrust, Western Qilian Shan, China by Yanxiu Shao, Daoyang Yuan, Michael E. Oskin, Pengtao Wang, Jing Liu-Zeng, Cuiping Li, and Zhao Wu Abstract Historical archives of earthquake occurrence provide a millennial view of fault system behavior with precision beyond the capability of radiometric dating tech- niques. Understanding the long historical record of earthquake activity in China presents a great opportunity to develop such an archive. However, the complex dis- tributed nature of faulting here leads to uncertainty and requires matching historic events to the paleoseismic record from fault excavations. We present paleoseismic evidence for the most recent rupture of the north Danghe Nanshan thrust (NDNT) and correlate the age of this event to nearby historical archives. We use high-resolution topography generated from airborne drone photography to measure an average coseis- mic fault throw of 0:8  0:2 m. Three trenches excavated across these small scarps show shortening of ∼1:3 m, consistent with event magnitude of M w 7:0  0:5 that probably ruptured the entire ∼45-km-long northern strand of the eastern NDNT sys- tem. Geochronology data and the historical record from Dunhuang and Anxi together indicate that this event likely occurred at A.D. 1289, during the Yuan Dynasty. Electronic Supplement: Description of the test procedure of optically stimulated luminescence (OSL) samples, and figure showing natural OSL decay curve, growth curves, and equivalent dose (De) distributions. Introduction Paleoseismic fault investigations are limited by the pre- cision of age-dating techniques and always face uncertainty in interpretation of earthquake magnitude from a strati- graphically recorded event. Historical earthquake records overcome these limitations, revealing the sequencing and ex- tent of strong shaking from events within a fault system. Within intracontinental regions, long recurrence intervals be- tween large earthquakes limit calibration of the seismic po- tential and clustering of activity across such fault systems. It is therefore important to extend the available record back into history and combine historical sources with geological map- ping and trenching. The historical earthquake record from an- cient China is long (∼4000 yrs; Xie and Cai, 1983) and spans a complex network of potential earthquake sources. This com- plexity and depth provides a valuable window into fault sys- tem behavior that compliments that documented in the near east along plate-boundary transform faults (e.g., Klinger et al., 2003, 2015). However, this complexity also magnifies the task of correlating earthquakes to paleoseismic events. Central government official documents and local annals probably seldom missed large earthquakes within the heart of the ancient Chinese empire. However, in remote impover- ished areas, with fewer residents, such records are scarce and less complete. Historical earthquake records may also be in- complete due to a reticence to record destructive events (Liu- Zeng et al., 2015). This study focuses on the north Danghe Nanshan thrust (NDNT), located in the western Qilian Shan and near Dunhuang. This city was within a remote border region of the Chinese empire during most of its history. The city is near the Mogao Grottoes, a set of Buddhist shrines that were damaged by historical earthquakes, according to writ- ten archives (Yuan et al., 2000). Here, we document and date evidence for recent surface rupture along the NDNT, and we suggest that evidence for this event was recorded at Dun- huang in the year A.D. 1289. Background The NDNT splays from the Altyn Tagh fault at the Xish- uigou triple junction, near Subei (Fig. 1), and plays a role in transforming shear strain along the Altyn Tagh fault to con- vergence (Meyer et al., 1998; Van der Woerd et al., 2001). Near Subei, the NDNT forms a 20-m-high fault scarp with Neogene rock uplifted in the hanging wall and exposed in 1175 Bulletin of the Seismological Society of America, Vol. 107, No. 3, pp. 1175–1184, June 2017, doi: 10.1785/0120160289