山东半岛东北部新发现近EW向活断层

A NEWLY DISCOVERED E-W-TRENDING ACTIVE FAULT IN THE NORTHEAST PART OF SHANDONG PENINSULA

山东半岛东北部地区晚第四纪的构造活动以整体性抬升为主,内部的断裂活动相对较弱,晚更新世以来的断裂活动仅分布在局部地区,新发现的东殿后断裂是其中的1条。断裂总体走向近EW,全长约20km,地貌上表现为由3条河流上游组成的谷地。断裂错断的最新地层的热释光年龄为84～75kaBP,上覆坡积角砾层的热释光年龄为64kaBP,断裂发育的松软断层泥的热释光年龄为82kaBP。断裂的剖面特征和断盖地层的年龄表明,东殿后断裂的最新活动时代是晚更新世早中期,垂直活动速率不<016mm/a,晚更新世晚期以来停止活动;断裂的最大潜在地震为6级。

Late Quaternary tectonic movement in the northeast part of Shandong Peninsula was dominated mainly by integral uplift, while fault activity inside the peninsula was relatively weak. Late Pleistocene faults are limited to some local areas, and one of them is the newly discovered Dongdianhou Fault. The fault is located to the north of Taiboding Mountains, associated with a broad fracture zone of 100m wide. Outcrops of fault profile can be observed in many places along the fault strand. The fault has a general strike of nearly East West and a total length of about 20km. Geomorphically, the fault appears as a straight fault valley consisting of 3 upper reaches of stream. The mountains on the southern side of the fault are obviously higher than those on the northern side. The cross section of the fault to the west of Xinshangzhuang Village shows that the fault displaces the unconsolidated rubble bed dated to be 84～75ka BP in age, resulting in a 1 8m high colluvial wedge, which is overlain by talus bed dated to be 64ka BP in age. The vertical slip rate of the fault is estimated roughly to be about 0.16mm/a. Soft fault gouges were observed on the fault planes exposed to the south of Diaoyushi Village and to the east of Taoyuan Village, and the age of the gouges is dated by thermoluminescent method to be 82ka BP. The characteristics of the fault and the age of overlying layers indicate that the latest faulting event occurred in early and middle stage of Late Pleistocene, while since the late stage of Late Pleistocene the fault has not ruptured the surface. According to the relation between surface rupture parameters and earthquake magnitude, it is estimated that the magnitude of the maximum potential earthquake on this fault is 61/2