SEISMOLOGY AND GEOLOGY ›› 2017, Vol. 39 ›› Issue (3): 587-604.DOI: 10.3969/j.issn.0253-4967.2017.03.011

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LATE QUATERNARY FAULTED LANDFORMS AND FAULT ACTIVITY OF THE HUASHAN PIEDMONT FAULT

XU Wei1, YANG Yuan-yuan2, YUAN Zhao-de1, LIU Zhi-cheng1, GAO Zhan-wu1   

  1. 1 China Earthquake Disaster Prevention Center, Beijing 100029, China;
    2 Anhui Earthquake Administration, Hefei 230031, China
  • Received:2016-04-27 Revised:2016-10-18 Online:2017-06-20 Published:2017-07-20

华山山前断裂断错地貌及晚第四纪活动性

徐伟1, 杨源源2, 袁兆德1, 刘志成1, 高战武1   

  1. 1 中国地震灾害防御中心, 北京 100029;
    2 安徽省地震局, 合肥 230031
  • 通讯作者: 高战武,副研究员,E-mail:515214334@qq.com
  • 作者简介:徐伟,男,1986年生,2011年于中国地震局地壳应力研究所获活动构造专业硕士学位,现主要从事地震地质、活动构造、第四纪地貌研究,电话:13426220213,E-mail:xwazhy@163.com。
  • 基金资助:
    地震科技星火计划项目(XH15053Y)与中国重点监视防御区活动断层地震危险性评价项目:华山山前断裂地质填图(14406033402)共同资助

Abstract: Based on the 1︰50000 active fault geological mapping, combining with high-precision remote imaging, field geological investigation and dating technique, the paper investigates the stratum, topography and faulted landforms of the Huashan Piedmont Fault. Research shows that the Huashan Piedmont Fault can be divided into Lantian to Huaxian section (the west section), Huaxian to Huayin section (the middle section) and Huayin to Lingbao section (the east section) according to the respective different fault activity.
The fault in Lantian to Huaxian section is mainly contacted by loess and bedrock. Bedrock fault plane has already become unsmooth and mirror surfaces or striations can not be seen due to the erosion of running water and wind. 10~20m high fault scarps can be seen ahead of mountain in the north section near Mayu gully and Qiaoyu gully, and we can see Malan loess faulted profiles in some gully walls. In this section terraces are mainly composed of T1 and T2 which formed in the early stage of Holocene and late Pleistocene respectively. Field investigation shows that T1 is continuous and T2 is dislocated across the fault. These indicate that in this section the fault has been active in the late Pleistocene and its activity becomes weaker or no longer active after that.
In the section between Huaxian and Huayin, neotectonics is very obvious, fault triangular facets are clearly visible and fault scarps are in linear distribution. Terrace T1, T2 and T3 develop well on both sides of most gullies. Dating data shows that T1 forms in 2~3ka BP, T2 forms in 6~7ka BP, and T3 forms in 60~70ka BP. All terraces are faulted in this section, combing with average ages and scarp heights of terraces, we calculate the average vertical slip rates during the period of T3 to T2, T2 to T1 and since the formation of T1, which are 0.4mm/a, 1.1mm/a and 1.6mm/a, and among them, 1.1mm/a can roughly represent as the average vertical slip rate since the middle stage of Holocene. Fault has been active several times since the late period of late Pleistocene according to fault profiles, in addition, Tanyu west trench also reveals the dislocation of the culture layer of(0.31~0.27)a BP. 1~2m high scarps of floodplains which formed in(400~600)a BP can be seen at Shidiyu gully and Gouyu gully. In contrast with historical earthquake data, we consider that the faulted culture layer exposed by Tanyu west trench and the scarps of floodplains are the remains of Huanxian MS8½ earthquake.
The fault in Huayin to Lingbao section is also mainly contacted by loess and mountain bedrock. Malan loess faulted profiles can be seen at many river outlets of mountains. Terrace geomorphic feature is similar with that in the west section, T1 is covered by thin incompact Holocene sand loam, and T2 is covered by Malan loess. OSL dating shows that T2 formed in the early to middle stage of late Pleistocene. Field investigation shows that T1 is continuous and T2 is dislocated across the fault. These also indicate that in this section fault was active in the late Pleistocene and its activity becomes weaker or no longer active since Holocene.
According to this study combined with former researches, we incline to the view that the seismogenic structure of Huanxian MS8½ earthquake is the Huashan Piedmont Fault and the Northern Margin Fault of Weinan Loess, as for whether there are other faults or not awaits further study.

Key words: Huashan Piedmont Fault, faulted landform, late Quaternary, fault activity

摘要: 基于华山山前断裂1︰5万活动断层填图成果,对断裂沿线地层地貌、断层三角面、河流阶地、陡坎地貌以及典型断错剖面等进行了详细的研究。研究表明:1)华山山前断裂按几何结构、断错地貌表现分西段(蓝田-华县段)、中段(华县-华阴段)及东段(华阴-灵宝段)3段;2)西段及东段断裂错断了T2阶地及马兰黄土,T1阶地跨断裂连续,测年结果表明,T2阶地形成于晚更新世中期,T1阶地形成于全新世早期,由此得出西段及东段断裂在晚更新世有过活动,全新世以来活动弱或不活动;3)中段断错地貌显著,河谷两侧发育Ⅲ级阶地,跨断裂阶地均被错断,测年结果表明:T1阶地形成于2~3ka BP,T2阶地形成于6~7ka BP,T3阶地形成于60~70ka BP,结合阶地陡坎高度,得出不同时段的平均垂直滑动速率:T3-T2时期0.4mm/a;T2-T1时期1.1mm/a;T1以来1.6mm/a;4)中段在晚更新世晚期以来发生过多次活动,在石堤峪、沟峪等地见漫滩陡坎,结合文化层及炭样年龄,可知漫滩形成于距今400~600a,对比历史地震资料,漫滩陡坎应为华县1556年地震的遗迹;5)结合前人研究认为,公元1556年华县8(1)/(2)级地震的发震构造为华山山前断裂及渭南塬前断裂,其它断裂是否参与有待进一步研究。

关键词: 华山山前断裂, 断错地貌, 晚第四纪, 活动性

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