山东安丘-莒县断裂小店子—茅埠段新活动及其定量研究

QUANTITATIVE ANALYSIS OF RECENT ACTIVITY OF THE XIAODIANZI-MAOBU SEGMENT OF THE ANQIU-JUXIAN FAULT, SHANDONG PROVINCE

小店子—茅埠段是沂沭断裂带安丘-莒县断裂的组成部分,北起莒县小店子东北,南至莒县茅埠以南,总体走向10°～20°,倾向NW或SE,倾角60°以上,长约30km。可细分为5小段,从北到南依次是小店子—齐家庄、源河、库山—西莲池、青峰岭和三庄—宅科小段。各小段之间为左阶或右阶斜列,平面上呈向北收敛、向南撒开的帚状。断裂在卫片和航片上都显示出清楚的线性影像,地貌上表现为清楚的基岩陡坎。根据野外所获得的天然和探槽剖面以及年龄样品测试结果,确定其最新活动时代为全新世早期,活动性质是以右旋走滑为主兼挤压逆断。距今约70ka以来,断裂的右旋位移量64～73m,位移速率0.91～1.04mm/a。距今约12ka以来,断裂的右旋位移量5.5～7.8m,位移速率0.46～0.65mm/a;垂直位移量2～3.8m,位移速率0.17～0.32mm/a。

The Xiaodianzi-Maobu segment is part of the Anqiu-Juzian Fault in the Tancheng-Lujiang Fault zone. It starts from northeast of Xiaodianzi village, Juxian County in the north and terminates at Maobu, Juxian County in the south. The fault segment has a general strike of 10°～20°, dipping northwest or southeast at an angle of 60°, and has a length of about 30km. The segment can further be divided into 5 sub-segments: the Xiaodianzi-Qijiazhuang, Yuanhe, Kushan-Xilianci, Qingfengling and Sanzhuang-Zhaike sub-segments from north to south successively. These 5 sub-segments are aligned in right- or left-step en-echelon, appearing as a brush structure converging to the north and diverging to the south. The fault segment appears as distinct lineation on satellite image or aerial photo, and geomorphically, as distinct bedrock scarp. According to field observation on natural exposures or trench logs, as well as dating results of samples collected from the fault segment, it can be deduced that the latest faulting event occurred in early Holocene and was dominated by right-lateral strike-slip with compressional reverse faulting component. The distinct horizontal fault striate is well developed along the fault plane and the drainage system crossing the fault segment is right-laterally distorted. This corroborates the right-lateral strike-slip of the fault segment. Field measurement of displacement and dating of the relevant samples have indicated that the displacement amount of the fault is 64～73m, and the displacement rate is 0.91～1.04mm/a in the past 70ka, while in the past 11ka, the displacement is 5.5～7.8m and displacement rate is 0.46～0.65mm/a. The reverse faulting along the fault segment can also be recognized in exposures or trench logs. It can be observed that the Cretaceous or Paleocene system is thrusted over the Quaternary system, making a distinct fault scarp landform. Field measurement of fault scarp and laboratory dating of relevant samples have revealed that in the past 11ka the vertical displacement along the fault segment is 2.3～3.8m and the displacement rate is 0.17～0.32mm/a. In the same period, the right-lateral displacement is 2～3 times as large as the vertical displacement.