Relationship between the Landslides Triggered by the Tongwei M7 1/2 Earthquake in 1718 AD and the Disappearance of Yongning Ancient Town

Although China''s historical earthquake documentation is relatively rich, it is not all based on scientific records. Therefore, the verification of the seismic information in historical records can effectively avoid exaggerating or underestimating the damage they produced. In this paper, we analyze the detailed information of the 1718 AD Tongwei M7 1/2 earthquake through field surveys, document sorting, and manual visual interpretation of UAV images. Major conclusions are listed as follows:①The low-level terraces of Weihe River between Gangu and Wushan are fully developed with flatted surface, and the residents here are mostly killed by house collapses. In addition, the disappearance of Yongning Ancient Town is not directly related to the earthquake-induced landslides; ② In fact, "Yongning Town is entirely buried by the earthquake" in the historical records describes the phenomenon that loess dust has pervaded the entire Weihe Valley. These dust grains are produced by the sliding of earthquake-induced landslides. Thus, there is no possibility that large-scale landslides have slipped over Weihe bedrock and buried Yongning Town; ③After the earthquake, survivors abandoned the ruins and selected a new site to live. They built a new town named "Pan''an (means always peaceful in the future)". earthquake-induced landslides may be the reason of burying the residential areas on valley-side slopes, while those locations inside the valley are associated with the amplification effect of ground vibration. On the basis of compiling historical seismic data, scientific methods are used to explore the real meaning of these documents, for the purpose of providing basic data for the risk evaluation of strong historical earthquakes.