关键词: 历史古滑坡, 小江断裂南段, 1606年建水地震, 发震构造

Abstract: Historical seismic data plays an important role in the study of seismicity and the evaluation of seismic risk, while earthquake-triggered landslides distributed with clustering features along active faults can provide key clues for identifying and assessing historical earthquakes. Based on remote sensing interpretation and field investigations, landslides with different scales have developed in more than 10 locations along the southern segment of the Xiaojiang Fault (XJF), which are ancient landslides with a stable state. These landslides are mainly distributed in basins and their border areas with gentle terrain slopes. They are likely to be earthquake landslides rather than rainfall induced. The main scarp angles of these landslides are relatively concentrated, most of them are between 29-31 degrees, indicating that these landslides are caused by one geological event. Some of them are large with a volume of more than 1 million m3, and some of them are small with a volume of less than 100,000 m3. The analysis results presented in this paper suggested that there is a close relationship between these landslides and the latest surface ruptures of the southern segment of the XJF, indicating that these landslides should be triggered by the latest seismic event along the southern segment of XJF. Based on the age test results of samples from the trench on the landslide body and historical literature data, the co-seismic landslides were triggered in 1606 AD. According to the latest research results of the earthquake surface rupture zone in the southern segment of the XJF and empirical formula, combined with the comparative analyzing the intensity of geological disasters and the number of casualties of different earthquake cases, the authors rechecked the magnitude of the 1606 Jianshui earthquake, showing that the magnitude of this historical earthquake could be not less than 71/2 (≥7.5). It means that the southern segment of the XJF, as the part of Xianshuihe-Xiaojiang fault (XSH-XJF) system, have the strong activity and ability to generate large earthquakes. GPS observations have verified that the crustal material on the southeastern margin of the Tibetan Plateau rotates clockwise around the Eastern Himalaya Tectonic Structure (EHS), which requires a continuous left-lateral strike-slip fault system as the eastern boundary. The results presented in this paper are useful for deeper study of such an eastern boundary.

Key words: Ancient landslides, Southern segment of Xiaojiang fault, 1606 Jianshui Earthquake, Seismogenic structure