Abstract:

Based on the 1: 50 000 geological mapping of active fault, the paper investigates the stratum, topography and faulted landforms of the northern marginal fault of Emei Platform, and preliminarily divides the northern marginal fault of Emei Platform into three sections by two stepovers near Tanjiazhuang Village and Nanliu Village according to different fault activity of each section.
At west of Tanjiazhuang Village is a loess platform, and the high terrain scarp can be seen from the northern margin. The height of scarp decreases progressively and the slope becomes gentle westwards at the place between Nanchi Village and Xikang Village, and to the place near Xiaoliang town, we cannot see obvious terrain scarps. The faulted sections can only be seen in the gullies which cross the terrain scarp at the south of Guozhuang Village and Tanjiazhuang Village. The fault dislocates the Pliocene red clay and the middle Pleistocene Lishi loess and covered by Malan loess; continuous paleosoil can be seen across the terrain scarp in some gullies. These indicate that in this section the fault was active in the early middle Pleistocene and its activity becomes weaker or no longer active after that.
The fault in the section between Tanjiazhuang Village and Nanliu Village can be divided into three parts by Shidian Village and Jinming Village, which are named, from west to east in sequence according to each faulted landform, the northern marginal fault of lacustrine terrace, the piedmont fault of Zijin Mountain and the northern marginal fault of loess platform. The fault transition area between each part is continuous and the fault is in linear distribution, so we see the whole fault section as having the same activity. In this section the Holocene diluvial fan is faulted. At least two plaeoearthquake events happened since Holocene, and the latest activity is in (2.00～1.29) ka BP according to Renzhuang trench and Jinsha trench, which can be well compared with former researches. The fault slip rate is over 0.33mm/a in the section south of Maguduo Village and is more than 0.36mm/a according to Renzhuang trench since the later period of the late Pleistocene.
In the section between Nanliu Village and Xizhangpo Village, the fault distributes along the frontal edge of the diluvial platform and is covered by thick loess. A 50～200m high linear terrain scarp formed due to the activity of fault can be seen along the frontal edge especially in the part between Xunwang Village and Xulu Village. At north of Wuzhai Village, the height of scarp decreases progressively and to the place near Xizhangpo Village, the terrain scarp cannot be seen clearly. In this section, Malan loess is faulted, which indicates that this fault section has been active since the late Pleistocene, but the evidence of Holocene fault activity has not been obtained yet due to the non-development of Holocene stratum. The fault slip rate is no less than 0.1mm/a since the late Pleistocene according to the faulted section at south of Xunwang Village.

Key words: Emei Platform, northern marginal fault, late Quaternary, fault activity

摘要：

通过1/5万活断层地质填图, 对山西峨嵋台地北缘断裂晚第四纪活动性进行了详细研究.以谭家庄、南柳附近的2个阶区为界, 将断裂分为西、中、东3段.谭家庄以西该断裂中更新世早期有过活动, 之后未见明显活动迹象.谭家庄至南柳之间断裂晚更新世以来活动强烈, 全新世仍有活动, 最新活动发生在(2.00～1.29)ka BP, 晚更新世晚期以来滑动速率≥0.36mm/a.南柳至西彰坡段晚更新世以来活动明显, 尚未发现全新世活动的直接证据, 晚更新世以来断层滑动速率≥0.1mm/a.

关键词: 峨嵋台地, 北缘断裂, 晚第四纪, 活动性