琼北老城剖面记录的马袅—铺前断裂西段晚更新世活动历史

Late Pleistocene Tectonic History of the Western Segment of Maniao-Puqian Fault: Evidence from the Laocheng Section,Northern Hainan Island

马袅-铺前断裂为1605年海南琼山7.5级大地震的发震断裂之一,其活动历史研究对琼北地区地壳稳定性评价、防震减灾以及琼州海峡跨海大桥等重大工程建设有重要意义。地质地貌调查结果表明,马袅-铺前断裂西段由三条近东西向平行展布的北倾阶梯状正断层组成,并构成南北宽约2.5 km的断裂带。老城人工开挖南北宽达70 m的断裂带剖面揭露了该断裂晚更新世活动历史,道堂组光释光(OSL)年代学测试结果表明断裂在距今16~31 ka期间经历了两期活动:第一期表现为南、北相向倾斜的正断活动,累计垂直位移3.3 m;第二期为南倾的正断活动,活动强度较大。马袅-铺前断裂错断不同时代地层的位移量表明该断裂自上新世以来开始活动,第四纪活动强烈,现今仍是琼北控制地震活动的重要断裂。

Maniao-Puqian Fault is an important seismogenic fault for the M7.5 Qiongshan earthquake in Hainan in 1605.Its tectonic history is of great significance for evaluating the crustal stability,earthquake risk mitigation,and the engineering of major construction projects such as the bridge connecting Hainan island and Leizhou peninsula.Geological and geomorphic studies show that the western segment of Maniao-Puqian Fault zone is about 2.5 km wide from north to south,and composed of three near-E-W-trending subparallel stepped normal faults.Fault profile excavation in Laocheng town exposed a wide(~70 m)N-S-trending fault zone,which reveals the fault tectonic history.Optically stimulated luminescence(OSL)dating results of the Daotang Formation indicate that the fault had experienced two tectonic events in 16-31 ka BP:an earlier N-/S-dipping normal faulting with a 3.3 m cumulative vertical displacement,followed by an intensive S-dipping normal faulting.Stratigraphic displacement in different ages indicates that the Maniao-Puqian Fault has been active since Pliocene,and its activity is strong in the Quaternary.It remains an important active fault in northern Hainan island.