Surface Rupture of the 1515 Yongsheng Earthquake in Northwest Yunnan, and Its Seismogeological Implications

The 1515 M7 3/4 Yongsheng earthquake is the strongest earthquake historically in northwest Yunnan. However, its time, magnitude and the seismogenic fault have long been a topic of dispute. In order to accurately define those problems, a 1: 50000 active tectonic mapping was carried out along the northern segment of the Chenghai-Binchuan fault zone. The result shows that there is an at least 25 kmlong surface rupture and a series of seismic landslides distributed along the Jinguan fault and the Chenghai fault. Radiocarbon dating of the C-14 samples indicates that the surface rupture should be a part of the deformation zone caused by the Yongsheng earthquake in the year 1515. The distribution characteristics of this surface rupture indicate that the macroscopic epicenter of the 1515 Yongsheng earthquake may be located near Hongshiya, and the seismogenic fault of this earthquake is the JinguanChenghai fault, the northern part of the Chenghai-Binchuan fault zone. Striations on the surface rupture show that the latest motion of the fault is normal faulting. The maximum co-seismic vertical displacement can be 3.8 m, according to the empirical formula for the fault displacement and moment magnitude relationship, the moment magnitude of the Yongsheng earthquake was Mw 7.3-7.4. Furthermore, combining published age data with the C-14 data in this paper reveals that at least four large earthquakes of similar size to the 1515 Yongsheng earthquake, have taken place across the northern segment of the Chenghai-Binchuan fault zone since 17190 +/- 50 yr. BP. The in-situ recurrence interval of Mw 7.3-7.4 characteristic earthquakes in Yongsheng along this fault zone is possibly on the order of 6 ka.