Evidence of multistage late Quaternary strong earthquakes on typical segments of Longmenshan Active Fault Zone in Sichuan, China

Abstract

Investigation of offset landforms and trench excavation are important means to acquire the evidence of multistage activities of active faults. Here we present the result of fault trough investigation in Beichuan County and the Pingtong Town of Pingwu County along the Longmenshan Central Fault Belt, as well as the result from trench excavation at the platform foreslope in Hanwang Town of Mianzhu County on the Longmenshan Front Range Fault Belt. These results show that at least three fault activity events, including the Wenchuan earthquake, occurred in the Beichuan fault trough, at least two, including the Wenchuan earthquake, at Pingtong fault trough, and 2–3 paleoearthquakes in the Hanwang trench. Among these three localities, the times of the last strong earthquake prior to Wenchuan earthquake at Beichuan fault trough and Hanwang trench are close, approximately 6000 years ago, i.e., greater than 5.8 ka and smaller than 6.63 ka ago. This provides the evidence of synchronous activity of the Central Fault Belt and the Front Range Fault Belt of the Longmenshan Active Fault Zone during the previous strong earthquake activities prior to Wenchuan earthquake.