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A continuous 13.3-ka paleoseismic record constrains major earth- quake recurrence in the Longmen Shan collision zone
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  • Wei Shi,
  • Hanchao Jiang,
  • G Ian Alsop,
  • Guo Wu
Wei Shi
Institute of Geology, China Earthquake Administration
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Hanchao Jiang
Institute of Geology, China Earthquake Administration

Corresponding Author:[email protected]

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G Ian Alsop
University of Aberdeen
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Guo Wu
Institute of Geology, China Earthquake Administration
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Abstract

Key Points: • The recurrence time of large earthquakes (M ï¿¿ 8.1) is 1200 years in the Long-men Shan collision zone. • MMI ï¿¿ ï¿¿½ (M ï¿¿ 5.9, R min ï¿¿ 10 km) is the lower-bound conditions for triggering the deformation in the Lixian lacustrine sediments. • The Maoxian-Wenchuan fault is the main fault that triggered the deformation in Lixian lacustrine sediments. Abstract The thrust collision zone with a low slip rate along the plate boundary is the main stress accumulation area and prone to occur more destructive earthquakes with a longer recurrence interval. Such region is often classified as low seismic risk if lack of continuous records of large earthquakes, such as the eastern Ti-betan Plateau before the 2008 M w 7.9 Wenchuan earthquake. Here, we provide a continuous seismic record in the Longmen Shan thrust fault zone spanning 13000 years based on detailed investigation of the soft-sediment deformation structures and seismites in the Lixian lacustrine sequence. The recurrence time of large earthquakes (M ï¿¿ 8.1) is 1200 years, which is significantly shorter than the previous estimate of 2000-6000 years. The Maoxian-Wenchuan fault is the main fault that triggered the deformation in the Lixian lacustrine sediments. In addition, the frequency of earthquake recurrence in the warm period is more frequent than that in the cold period, which should arouse our attention on the seismic study in the tectonically active regions. Plain Language Summary The Longmen Shan fault zone was evaluated as a low seismic risks area before 2008 because of complete failure of trenching paleoseismic research in the eastern Tibetan Plateau, which led to the severe casualties and property losses caused by the 2008 Wenchuan Ms 8.0 earthquake. Therefore, it is urgent to explore new research methods to reveal the paleoseismic records in the eastern 1 Tibetan Plateau. Continuous lacustrine deposition is a good carrier for revealing tectonic events. The soft-sediment deformation and seismites recorded in lacustrine sediments can be good indicators of paleoseismic event. Here, we redefined the soft-sediment deformation and seismic records of the Lixian lacus-trine sediments in the Longmen Shan fault zone, and discussed the recurrence time and recurrence model of regional earthquakes by linking them with earthquake intensity. We obtain that much shorter recurrence interval (1400 years) of large earthquakes (M ï¿¿ 8.1) are recorded in the Lixian lacustrine sediments compared with earlier studies (2000-6000 years), and the large earthquake have a random earthquake recurrence model of plate boundaries. These results are very important for reassessing the seismic risk of the Longmen Shan fault zone in the eastern Tibetan Plateau.