A 43,000-Year-Long Paleoseismic Record Along the Southern Section of the Lijiang-Xiaojinhe Fault, Southeastern Tibetan Plateau, China

Abstract

Paleoseismic data on the timing of ground-rupturing earthquakes can help identify the sources of historical earthquakes and define the extent of seismic rupture gaps. The Lijiang-Xiaojinhe fault (LXF) is a left-lateral strike-slip fault that stretches 380 km along the southeastern margin of the Tibet Plateau, passing through the densely populated urban area of Lijiang City. In this study, we excavated four paleoseismic trenches at the Shuijing and Haitang sites along the southwestern section of the LXF and identified eight earthquakes over the past 43 Kyr through detailed trench logging and radiocarbon dating. The average recurrence interval (RI) for these eight events is 6.0 ± 4.8 Kyr, with a coefficient of variation (COV) of 0.80, indicating that earthquake recurrence is weakly periodic. In contrast, the average RI for the last five events is 3.1 ± 2.3 Kyr, with a COV of 0.72, indicating a stronger periodic behavior. Analyzing historical earthquake documents revealed that the most recent event corresponds to the M 6.8 Jianchuan earthquake in 1751 and may have involved a joint rupture along the LXF and the Zhongdian-Longpan-Qiaohou fault. Comparison with other sites along the LXF limits the extent of a seismic rupture gap to ∼70 km long between Lijiang and Ninglang. This gap has not experienced earthquakes for ∼2,000 years and accumulated a coseismic slip of ∼4.3 m, impending a large earthquake of Mw 7.2–7.6. Consequently, Lijiang City is currently at high risk of a large earthquake.