THE HOLOCENE ACTIVE EVIDENCE ON THE LONGCI-YUKOU SEGMENT OF LUOYUNSHAN FRONTAL FAULT ZONE,SHANXI

doi:10.3969/j.issn.0253-4967.2011.04.010

Abstract

Abstract:

The 145-km-long,southeast-dipping and normal-faulting with dextral slip Luoyunshan frontal fault zone controls the western edge of NE-trending Linfen Basin which locates at the southwestern part of the Shanxi fault-depression system.Two historic strong earthquakes successively occurred in the Linfen Basin: the A.D.1695 Linfen M7 1/2 and the A.D.1303 Hongdong M8 earthquakes.In the previous work,based on distribution features of the fault that it is intersected by three NW-trending faults and its strike changes abruptly at Fanjiazhuang village,the fault is divided into five segments: Wanshengsi-Tumen,Tumen-Yuli,Yuli-Weicun,Weicun-Fanjiazhuang,and Fanjiazhuang-Xiweikou.And its Quternary activity history is divided into three phases: end of Middle Pleistocene to early of Late Pleistocene,end of Late Pleistocene to early of Holocene and Holocene.Quaternary deposition thickness and deposition rate of the Tumen-Yuli segment are prominent along the Luoyunshan frontal fault zone.Longci depression center is adjacent to the fault and extends along its direction.Cenozoic strata is 1800meters thick,including 1100meters thick of Pliocene strata and 700meters thick of Quaternary strata,indicating a gradually increased trend of depression's deposition and the most intensive activity.Many previous studies show that the segment is active in Holocene.However,few of these studies have provided authentic geologic evidence.Paleoseismic trenching and fault geomorphologic investigation provide effective methods to obtain the most recent activity parameters of active faults.Applying these methods,this paper makes some breakthroughs on the most recent activity of Longci-Yukou segment along the Luoyunshan frontal fault zone on the western boundary of Linfen Basin.Research indicates that tectonic geomorphologic scarps with heights of 2.5m±,5.2m± and 8m±,respectively,present continually on these alluvial fanheads; the terraces T₁ of gully around Longci are dated to be about 7500a BP; terraces with heights of 3.5m±,8m±,18m± above the gully base,respectively,in the NW-trending Xifanggou are related to the scarps; the Xifanggou trench exposure records five surface-rupturing paleoearthquake events since late Pleistocene and the youngest event in the trench probably occurred in Holocene,sometime after(7.52±0.1)ka,which is significant for protecting against and mitigating earthquake disasters in the Linfen Basin.

Key words: Luoyunshan frontal fault zone, alluvial fanhead scarps, Holocene activity, Linfen Basin

摘要：

通过断错地貌调查和探槽开挖,获得了临汾盆地西界罗云山山前断裂带龙祠-峪口段的最新活动信息: 该段山前洪积扇后缘断断续续存在高2.5m、5.2m、8m左右的地表地貌陡坎; 附近冲沟的Ⅰ级阶地热释光测年为距今7 500a左右; 在NW向的席坊沟内存在拔沟3.5m、8m、18m左右的3级阶地,与地貌陡坎有对应关系; 席坊沟探槽揭示罗云山山前断裂带断错了晚更新世晚期以来的地层,存在5次古地震事件,最新一次活动断错了¹⁴C测年为距今(7.52±0.1)ka的垆土层,这为临汾盆地的防震减灾决策提供了新的依据。

关键词: 罗云山山前断裂带, 洪积扇后缘陡坎, 全新世活动, 临汾盆地

CLC Number:

P315.2

XU Jian-hong, XIE Xin-sheng, SUN Chang-bin. THE HOLOCENE ACTIVE EVIDENCE ON THE LONGCI-YUKOU SEGMENT OF LUOYUNSHAN FRONTAL FAULT ZONE,SHANXI[J]. SEISMOLOGY AND GEOLOGY, 2011, 33(4): 855-864.

许建红, 谢新生, 孙昌斌. 山西罗云山山前断裂带中段龙祠-峪口全新世活动证据[J]. 地震地质, 2011, 33(4): 855-864.

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