蒙山山前断裂第四纪活动特征分析

Study on Quaternary Activities Characteristics of the Mengshan Piedmont Fault

蒙山山前断裂是鲁西地块一条较为活跃的NW向断裂,为研究其第四纪活动特征,本文综合运用野外观察、探槽剖面分析和年代测试等方法,结合重力异常特征,对蒙山山前断裂的最新活动性和深部构造进行了初步研究,对于评价蒙山山前断裂的地震危险性有重要意义。结果表明:①蒙山山前断裂第四纪以来以左旋走滑及正断运动为主。断裂以于家庄村为界,分为东西两段,西段在第四纪以来活动不明显,东段的主要活动时期为晚更新世;②蒙山山前断裂向深部下切至中下地壳,属深大断裂;③蒙山山前断裂在晚更新世以来可能发生过两次古地震事件,分别在(44.1±3.4)~(24.3±1.2) ka和(22.7±1.8)~(6.2±0.5) ka;④断裂带上曾发生过多次5级左右地震,具有发生中强地震的潜在风险,建议今后加强对该断裂的研究。

The Mengshan piedmont fault is a relatively active NW trending fault in the western Shandong block.In order to study its Quaternary activity characteristics,the latest activity and deep structure of the Mengshan piedmont fault have been preliminarily studied by using field observation,trench profile analysis,geochronology measurement and other methods in combination with gravity anomaly characteristics,which is of great significance for evaluating the seismic risk of the Mengshan piedmont fault.The results show that:①Since the Quaternary,the Mengshan piedmont fault is mainly characterized by sinistral strike-slip and normal fault movement.The fault,bounded by Yujiazhuang Village,is divided into east and west sections.The western section has not been active since the Quaternary,while the eastern section has been active mainly in the late Pleistocene.②The Mengshan Piedmont fault cuts deep to the middle and lower crust,which is a deep major fault.③There may have been two paleoseismic events in the Mengshan Piedmont fault since the late Pleistocene,(44.1±3.4)~(24.3±1.2)ka and(22.7±1.8)~(6.2±0.5)ka,respectively.④There have been many M≈5 earthquakes occurred in the fault zone,which has the potential risk of triggering moderate and strong earthquakes.It is suggested to strengthen the in-depth study of the fault in the future.