丽江-小金河断裂中段晚第四纪古地震历史  

LATE QUATERNARY PALEOEARTHQUAKES ON THE MIDDLE SEGMENT OF THE LIJIANG-XIAOJINHE FAULT,SOUTHEASTERN TIBET

作　　者：丁锐[1,2] 任俊杰[1] 张世民[1] 吕延武[1] 刘汉永[1] DING Rui;REN Jun-jie;ZHANG Shi-min;LU Yan-wu;LIU Han-yong(Key Laboratory of Crustal Dynamics,Institute of Crustal Dynamics,China Earthquake Administration Beifing 100085,China;State Key Laboratory of Earthquake Dynamics,Institute of Geology,China Earthquake Administration Beijing 100029,China)

机构地区：[1]中国地震局地壳应力研究所地壳动力学重点实验室,北京100085 [2]中国地震局地质研究所地震动力学国家重点实验室,北京100029

出　　处：《地震地质》2018年第3期622-640,共19页Seismology and Geology

基　　金：国家自然科学基金(41572193);中国地震局地震行业科研专项(201108001);中国地震局地壳应力研究所基本科研业务专项(ZDJ2017-24);中国地震局地质研究所地震动力学国家重点实验室项目(LED2016A01)共同资助;城市活断层探测与地震危险性评价项目:丽江-小金河断裂(丽江盆地隐伏段)地质填图项目

摘　　要：丽江-小金河断裂为川滇菱形块体内部重要的次级边界断裂,沿断裂断错地貌清晰,晚第四纪活动强烈,但历史上无地表破裂型地震的记录,其大震复发行为仍不清楚,难以评价其地震危险性。文中选取断错地貌最为显著的丽江-小金河断裂中段,在高分辨率卫星影像解译的基础上,在母猪达、红星和干塘子开挖3个探槽,并利用放射性碳测年和古地震事件的Ox Cal建模对古地震事件年龄进行了限定。研究结果表明,母猪达探槽揭示了3次古地震事件,分别发生在7 940~6 540a BP、4 740~4 050a BP和1 830~420a BP;红星探槽揭示了2次古地震事件,分别发生在5 120~3 200a BP和2 100~1 220a BP;干塘子探槽揭示了至少3次古地震事件,分别发生在44 980~17 660a BP、7 210~3 810a BP和2 540~1 540a BP,因为地层存在缺失,该探槽中揭示的事件可能不完整。综合3个探槽结果,全新世以来丽江-小金河断裂中段有3次古地震,分别发生在7 940~7 210a BP、4 740~4 050a BP和1 830~1 540a BP,其大震复发大致符合准周期模式,平均复发间隔约3 000a,震级达M7.5。考虑到丽江-小金河断裂中段较强的晚第四纪活动和较长的大震离逝时间,其未来地震危险性值得关注。More attention has been paid to the late Quaternary activity of the boundary fault of the SichuanYunnan block in eastern Tibet. The Lijiang-Xiaojinhe Fault（ LXF） locates along the boundary of the northwest Sichuan and central Yunnan sub-blocks in the Sichuan-Yunnan block. Clear displaced landforms show that the fault has undergone strong late-Quaternary activity. However there is no surface-rupturing earthquake occurring on the LXF in the historical record. The LXF crosses the city of Lijiang,one of the most important tourist cities in Southwest China. The rupture behavior on this fault remains unclear and it is hard to assess its seismic hazard in the future. In this study,on the base of the interpretation of high-resolution satellite imagery,we chose the middle segment of the LXF and dug three trenches at Muzhuda, Hongxing, and Gantangzi sites to constrain the ages of paleoearthquakes combined with radiocarbon dating and Ox Cal modeling. The Muzhuda trench shows that at least three events occurred on the middle segment of the LXF at 7 940 - 6 540 a BP,4 740 -4 050 a BP and 1 830 - 420 a BP,respectively. The Hongxing trench indicates that the LXF underwent two events at 5 120 - 3 200 a BP and 2 100 - 1 220 a BP. The Gantangzi trench reveals at least three paleoearthquakes at 44 980 - 17 660 a BP,7 210 - 3 810 a BP and 2 540 - 1 540 a BP,respectively. The events in the Gantangzi trench might be incomplete because of stratigraphic gap. These three trenches indicate that three events occurred on the middle segment of the LXF in the Holocene at 7 940 -7 210 a BP,4 740 - 4 050 a BP and 1 830 - 1 540 a BP,respectively. Large earthquakes on the middle segment of the LXF appear to fit the quasi-periodic model with the mean recurrence interval of- 3 000 a and the estimated magnitude 7. 5. Given the strong late-Quaternary activity of the middle segment of the LXF and a long elapsed time,we propose that the middle segment of the LXF might have a high seismic hazard potential in the near future.

关 键 词：川滇菱形块体 丽江-小金河断裂 古地震 探槽 复发间隔 

分 类 号：P315.2[天文地球—地震学]