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Title:: The Characteristic of Active Normal Faulting of the Southern Segment of Weixi-Qiaohou Fault

作者:: 常祖峰¹; 常昊¹; 李鉴林¹; 代博洋¹; 周青云¹; 朱家龙²; 罗宗其²; (1.云南省地震局,云南昆明 650224; 2.云南省巍山县地震办公室,云南巍山 672400)

Author(s):: CHANG Zufeng¹; CHANG Hao¹; LI Jianlin¹; DAI Boyang¹; (1.Earthquake Administration of Yunnan Province,Kunming 650224,Yunnan,China)(2.Yunnan Weishan Country Seismological Office,Weishan 672400,Yunnan,China)

Keywords:: the southern segment of Weixi-Qiaohou Fault; Weishan basin; normal fault; late Pleistocene; vertical slip rate

摘要:: 根据野外调查结果,重点阐述了维西—乔后断裂南段的活动特征。研究表明,维西—乔后断裂南段在第四纪表现出明显的活动特征,运动性质以正断层作用为主。维西—乔后断裂南段对巍山第四纪盆地有着明显的控制作用,因受其影响盆地内阶地不对称发育。箐门口、佛堂村、洗澡塘探槽揭示该断裂断错了晚更新世堆积,被错最新地层¹⁴C年龄(15 430±60)a B.P.,OSL年龄为(11.6±1.6)ka,表明其最新活动时代在晚更新世末期。洗澡塘村断层地貌清晰,西河Ⅱ级阶地上发育高2 m左右的断层陡坎。根据阶地断层陡坎高度和阶地面形成年龄估算,晚更新世以来该断裂段垂直滑动速率约为0.18～0.32 mm/a。

Abstract:: According to geological and geomorphic field observations,we mainly elaborate the active feature of the southern segment of Weixi-Qiaohou Fault.It is revealed that the fault is apparently active in Quaternary,behaving normal faulting primarily.The Weishan quaternary basin is apparently controlled by the fault,and the terraces in the basin have developed asymmetrically under its influence.It is documented that late Pleistocene accumulations with ¹⁴C age(1 5430±60)a B.P and OSL age(11.6±1.6)ka has been displaced by the fault,revealed by the exploratory trenches at Qingmenkou,Fotang and Xizaotang villages.Therefore,it suggests that the fault is newly active in late Pleistocene.The fault landform is clear at Xizaotang village,there is a 2 m high fault scarp on the T₂ terrace of the Xihe river.It is estimated the fault has a average vertical slip rate of 0.18～0.32 mm/a since late Pleistocene,based on displaced magnitude of the river terraces and their ages formed.