韩城断裂晚第四纪活动性研究

THE STUDY OF LATE QUATERNARY ACTIVITY OF HANCHENG FAULT

在1:5万活断层地质地貌填图的基础上,对韩城断裂的构造地貌特征及晚第四纪活动性进行了详细研究。依据断裂的构造地貌、活动性及几何展布特征等将断裂自北向南分为3段:西硙口至盘河段、盘河至行家堡段和行家堡至义井段。断裂的活动性自NE向SW是逐渐变弱的。西硙口至盘河段为典型的盆山地貌,全新世活动,全新世中期以来的垂直滑动速率估算>0.8mm/a;盘河至行家堡段,断裂沿黄土台地前缘展布,晚更新世晚期活动,晚更新世晚期以来的垂直滑动速率约为0.49mm/a;行家堡至义井段,断裂伸入渭河盆地北部黄土塬中,晚更新世早期黄土中发育裂隙及砂土液化现象。

Based on the 1 ： 50 000 geological and geomorphologic mapping of active fault, the structural geomorphic features and activity of Hancheng Fault are investigated in detail. In the study, we divide the fault into three sections from north to south： the section between Xiweikou and Panhe River, the section between Panhe River and Xingjiabao and the section between Xingjiabao and Yijing, the three sections show different characters of tectonic landform. The section between Xiweikou and Panhe River is a kind of typical basin-mountain landform, where diluvial fans spread widely. In the north of Yumenkou, the fault deforms the diluvial fans, forming scarps, along which the fault extends. In the south of Yumenkou, the fault extends along the rear edge of the diluvial fans. In the section between Panhe River and Xingjiabao the fault extends along the front of the loess mesa. In the section between Xingjiabao and Yijing the fault forms scarp in the loess and extends as an arc shaped zone, and the landform is formed by the accumulative deformation of the fault. The activity of the fault becomes weak gradually from northeast to southwest. The fault activity of the section between Xiweikou and Panhe River is the strongest, and the latest age of activity is Holocene. The slip rate since the mid-Holocene is bigger than 0. 8mm/a at Yumenkou. The fault activity of the section between Panhe River and Xingjiabao is weaker than the north part, the fault＇s latest active age is identified as the later period of Late Pleistocene and the activity becomes weak gradually from northeast to southwest. At the estuary of the Jushui River the slip rate of the fault is about O. 49mm/a since late Late Pleistocene. The fault activity of the section between Xingjiabao and Yijing is the weakest. There is no evidence of paleosol S1 deformed in fault profiles, and only some phenomena of fracture and sand liquefaction in the earlier Late Pleistocene loess. The activity of the fault is in line with the fault landform feature. At macro level, the relationship between the uplifted side and the thrown side of the fault switches gradually from the Ordos uplifting region and the rifted basin to the interior blocks of the rifted basin, which maybe is the regional reason why the activity of the Hancheng Fault becomes weak from the northeast to the southwest.