Paleoseismic evidence and repeat time of large earthquakes at three sites along the Longmenshan fault zone
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- 作者：Yongkang Ran ; Lichun Chen ; Jie Chen ; Hu Wang ; Guihua Chen ; Jinhui Yin ; Xiang Shi ; Chenxia Li ; Xiwei Xu
- 关键词：Longmenshan ; Wenchuan earthquake ; Paleoearthquake ; Recurrence of large earthquake
- 刊名：Tectonophysics
- 出版年：2010
- 出版时间：20 August 2010
- 年：2010
- 卷：491
- 期：1-4
- 页码：141-153
- 全文大小：1991 K
文摘
In historical records, no earthquake of magnitude comparable with that of the Wenchuan Mw 7.9 earthquake has ever been reported in Chengdu and Longmenshan regions. It is important, therefore, to assess if there is any evidence of prior large earthquakes in the recent geological record. In order to explore this problem, 3 trenches were excavated separately at 3 sites along the surface rupture zones in the middle segment of the Beichuan–Yingxiu Fault and Jiangyou–Guanxian Fault of the Longmenshan fault zone, and the offsets of geomorphic surfaces were measured in the trenches. The basic facts of recurrence of large earthquake on the seismogenic fault of the Wenchuan earthquake are demonstrated in this paper on the basis of the accumulated deformation amounts of old and young geomorphic surfaces as well as the paleoearthquake events revealed in the trenches. The document that at Leigu along the Beichuan–Yingxiu Fault, at Bailu along the Jiangyou–Guanxian Fault, and Xiaoyudong on a NW-trending fault, the height of fault scarp on the second terrace has a multiple relationship to that on the first terrace after the Wenchuan earthquake of 12, May. The elevation difference of the marker horizon (the yellow sandy clay bed) of the second terrace revealed in the trenches on both sides of the fault is nearly twice (or three times larger in Bailu) of that produced by the Wenchuan earthquake. These observations suggest the occurrences of paleoearthquake events with surface deformation comparable to that produced by the Wenchuan Mw 7.9 earthquake. According to the dating data and the fact that there is no such slip of comparable paleoearthquakes in the 2300-year-long historic literature in Longmenshan region, we suggest that the penultimate event occurred between 2300 a BP and 3300 a BP.