郯庐断裂带中段嶂山东侧断裂的活动特征

ACTIVITY FEATURES OF FAULTS AT THE EAST OF ZHANGSHAN ON THE MIDDLE SEGMENT OF TANLU FAULT ZONE

目前对于郯庐断裂带新沂—泗洪段的研究相对薄弱,通过对该段北侧构造地貌条件较好的嶂山段开展研究,充实了该段的晚第四纪活动证据与古地震事件序列。嶂山段总体位于宿迁市晓店镇至井头乡一带,长约7km。构造地貌研究显示嶂山段晚第四纪活动具有逆冲右旋的运动性质。古地震探槽研究揭示:1)郯庐断裂在该段具有分期活动特征,上新世期间为拉张正断,第四纪以来表现为逆冲;2)1次古地震发生在15.12~11.82ka BP;3)断裂最新活动年代可能为3500a BP左右。综合前人的研究成果,目前郯庐断裂带新沂—泗洪段已揭露的古地震事件年代序列可归纳为:9.6×10~4a以前,晚更新世早、中期,15.12~11.82ka BP,(11.76±0.05)^(10.53±0.05)ka BP,(10.15±0.05)^(8.16±0.05)ka BP,4960~3510a BP。

Given the scarcity of research on the activity of Xinyi-Sihong segment of the Tanlu Fault zone,this paper focuses on the Zhangshan segment where there are quite evident geomorphic features to complement the shortage of the research on the northern part of Xinyi-Sihong segment. This study enriches evidences for the late Quaternary activity and paleoseismological events on the Xinyi-Sihong segment. The Zhangshan segment is located at Xiaodian Town to Jintou Village of Suqian City,stretching towards NE for 7 kilometers with a dip angle of 60 ～ 80. Research of tectonic geomorphology shows that gullies in northern part of Zhangshan segment were evidently displaced,while in the southern,two NE-trending right-stepped fault scarps are developed,with an average height of 3 meters,which generally suggests that the fault was dominated by thrust and dextral motion. Two trenches were excavated in the southern part of Zhangshan segment,numbered Mayao trench 1 and Mayao trench 2. Both trenches reveal that：（ 1） within this segment,Tanlu Fault shows periodic fault activity, that is, normal faulting during Pliocene epoch while thrust faulting in Quaternary period;（ 2） an event occurred between 15. 12 ka BP to 11. 82 BP;（ 3） the latest event possibly took place around 3500 a BP. Based on integrated results of previous studies,we identify the dates of paleoseismic events on the Xinyi-Sihong segment as follows： more than 960 thousands years ago,early to middle period of late Pleistocene,（ 15. 12 ～ 11. 82） ka BP,（ 11. 76 ± 0. 05） ka ～（ 10. 53 ± 0. 05） ka BP,（ 10. 15 ± 0. 05） ka ～（ 8. 16 ± 0. 05） ka BP and 4960 ～ 3510a BP.