双山—李家庄断裂地表破裂特征与最新活动性研究

The Surface Rupture Characteristics and Latest Activities of the Shuangshan—Lijiazhuang Fault

利用地质地貌调查、探槽、工程探测以及年代测试等方法,对双山—李家庄断裂的地表破裂形态、最新活动性以及古地震事件展开研究。结果表明:(1)双山—李家庄断裂的最新活动时代为晚更新世,在(17.0±0.85)ka^(21.4±1.7)ka B.P.之间,总体以左旋走滑正断为主,局部逆断。依据第四纪活动特征和破裂形式,从南往北可分为两段,即南段(双山—大马山)和北段(大马山—五里)。其中南段又可分为3个小段:双山—丹河水库小段表现为左阶斜列状展布的两条断层,以左行走滑兼正断活动为主;丹河水库—营子小段表现为两条相交的断裂,东支在剖面上则表现为正断活动,第四纪以来不活动;西支在剖面上以逆冲破裂为主,最新活动时代为晚更新世;营子—大马山小段隐伏于第四系之下,具有正断走滑破裂特征。北段总体表现为多条近平行的断裂构造系,破裂形式以逆断为主。(2)双山—李家庄断裂晚第四纪以来可能发生过两次古地震事件,分别发生在(17.0±0.85)ka^(21.4±1.7)ka B.P.和(77.0±3.8)ka^(84.0±4.2)ka B.P.。(3)1829年青州、临朐6级地震的发生与上五井断裂和双山—李家庄断裂构成的"X"型共轭构造密切相关,双山—李家庄断裂很可能就是这次地震的发震构造。鲁西断块内发育的多条与双山—李家庄断裂相似的NW向晚更新世活动断裂,均具有发生6级左右地震的构造条件,因此,今后应加强这些断裂的活动断层探测和地震监测研究,为地震防御工作提供可靠依据。

By means of geological and geomorphological investigation,trenching,engineering exploration and dating,the surface rupture morphology,latest activities and paleoearthquakes of the Shuangshan-Lijiazhuang fault have been studied in this paper.The results show that:(1)The latest activity of the Shuangshan-Lijiazhuang fault occurred at the late Pleistocene,it is obviously dominated by left-lateral strike-slip faulting with normal components,and with thrusting components somewhere.According to the latest activities and geometry,it could be divided into 2 segments with the Shangwujing fault as the boundary,namely,the Shuangshan-Damashan segment(the south segment)and the Damashan-Wuli segment(the north segment).The south segment is characterized by left-lateral strike-slip motion and also consists of three sub-segments.The sub-segment between Shuangshan and Danhe Reservoir consists of two left-step en-echelon faults.The sub-segment from Danhe Reservoir to Yingzi Town consists of two intersected faults,among them the western branch is characterized by thrusting components and the late Pleistocene activities,while the eastern branch is characterized by normal faulting components and no Quaternary activities.The sub-segment between Yingzi and Damashan is covered by the Quaternary sediments and is dominated by left-lateral strike-slip motion with normal faulting.The north segment between Damashan and Wuli generally consists of multiple parallel thrust faults,which offsets the late Pleistocene strata.(2)Since the late Quaternary Period,two paleo-earthquakes probably occurred along the Shuangshan-Lijiazhuang fault.The lower part of the late Pleistocene strata was offset at the early event,and the upper part of the late Pleistocene strata was offset at the latest event.(3)The seismo-tectonics of the 1829 Qingzhou-Linqu M6■earthquake is the"X"tectonic system which consisted of the Shangwujing fault and the Shuangshan-Lijiazhuang fault,but the Shuangshan-Lijiazhuang fault is probably the dominant structure according to its latest actives.There are several other late Pleistocene faults besides the Shuangshan-Lijiazhuang fault in the Luxi faulted block.All of these active faults have tectonic conditions for earthquakes with magnitude 6 or over,so attentions should be paid to the earthquake monitoring and active fault surveying and prospecting for better earthquake disaster mitigation in near future.