藏南多庆错地堑冲巴雍错段最新史前大地震遗迹及其年龄证据  

THE LATEST PREHISTORIC EARTHQUAKE RELICS AND ITS AGE EVIDENCE IN CHONGBA YUMTSO FAULT SECTION OF DUOQING CO GRABEN,SOUTHERN TIBET

作　　者：左嘉梦 吴中海[1] 盖海龙 哈广浩 周春景[1] Zuo Jiameng;Wu Zhonghai;Gai Hailong;Ha Guanghao;Zhou Chunjing(Key Laboratory of Neotectonic Movement and Geohazard,Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081;China University of Geosciences(Beijing),Beijing 100083;Qinghai Earthquake Agency,Xining 810001,Qinghai;Key Laboratory of Active Tectonics and Volcanoes,Institute of Geology,China Earthquake Administration,Beijing 100029)

机构地区：[1]新构造运动与地质灾害重点实验室,中国地质科学院地质力学研究所,北京100081 [2]中国地质大学(北京),北京100083 [3]青海省地震局,青海西宁810001 [4]中国地震局地质研究所,活动构造与火山重点实验室,北京100029

出　　处：《第四纪研究》2020年第5期1323-1333,共11页Quaternary Sciences

基　　金：国家自然科学基金项目(批准号:41571013和41171009);中国地质调查局地质调查项目(批准号:DD20190396)共同资助。

摘　　要：西藏亚东-谷露裂谷是青藏高原南部规模最大的活动裂谷,但与其全新世强烈活动性不符的是该裂谷南段多庆错地堑历史上缺少MW≥6地震记录,因此通过古地震研究来揭示该区大地震活动与断裂活动性的关系显得十分重要。本文根据在亚东-谷露裂谷南段多庆错地堑冲巴雍错至多庆错段(范围:28°21'~27°52'N和89°44'~89°17'E)发现的最新史前大地震的地表破裂遗迹,初步研究了地震的时间与震级。通过高分辨率卫星影像解译、利用小型无人机获得的数字高程模型分析和详细的地表调查,发现该区最新史前大地震的同震破裂带在冲巴雍错段错断了河流T2及同期泉华台地,形成了最高约4.5 m的断层陡坎。根据断层陡坎上探槽中古土壤样品的AMS14C测年结果,揭示被错断的最新地层年龄为6460~3260 cal.a B.P.。综合分析认为,西藏亚东-谷露裂谷南段的多庆错地堑在约3260 cal.a B.P.之后至少发生过一次矩震级为MW7.1~7.2的大地震,该地震同时造成冲巴雍错段和多庆错段断裂破裂,总的破裂带长度可能达到62 km,最大地震位移可能大于4.5 m。新发现的多庆错地堑全新世古地震填补了亚东-谷露裂谷南段古地震研究的不足,并且有助于更深入地认识西藏亚东-谷露裂谷南段大地震活动历史和区域强震危险性。The Yadong-Gulu Rift(27°40'~28°42'N,89°05'~89°54'E)is the largest active rift in the southern Tibetan Plateau,but inconsistent with its strong Holocene activity there is a lack of MW≥6 seismic records in the Duoqing Co Graben,the southern segment of the rift.Paleoseismology was considered a valid method to reveal the relationship between large seismicity and fault activity in this area.The latest surface rupture traces of a prehistorical earthquake found in the range from Chongba Yumtso to Duoqing Co(28°21'~27°52'N,89°44'~89°17'E),preliminary study the time and magnitude of this earthquake.High-resolution satellite images,digital elevation model analysis obtained from the unmanned aerial vehicle(UAV)and detailed surface survey,were used to detect and analyze the coseismic displacement of a second stage terrace(T2)and the contemporaneous travertine platform,and a fault scarp was measured to around 4.5 m high.Further,the paleosol from this scarp was dated 6460 cal.a B.P.to 3260 cal.a B.P.using the AMS14C dating method.It is reasonable to think that at least an MW7.1~7.2 earthquake occurred after 3260 cal.a B.P.in Duoqing Co graben,forming the surface rupture between Chongba Yumtso and Duoqing Co,with a total length of up to 62 km,and a maximum coseismic displacement of 4.5 m.This found makes up for the deficiency of paleoearthquake research in the southern segment of the Yadong-Gulu Rift and contributes to deeply study the history of large earthquakes and regional strong earthquake risk to this area.

关 键 词：亚东-谷露裂谷 多庆错地堑 地震地表破裂 古地震 正断层 

分 类 号：P694[天文地球—地质学] P546