川西地区龙泉山断裂特征及活动性评价

发布时间：2018-03-25 14:45

本文选题：龙泉山断裂带　切入点：构造特征　出处：《成都理工大学》2015年硕士论文

【摘要】：2008年汶川地之后,四川盆地中活动性断裂的研究及地震危害性评价引起了广泛关注。而龙泉山断裂带距离成都市区不足20km,所经地区经济发达,人口稠密,是重要的农业和工业基地,因此其活动性评价尤为重要。龙泉山断裂带位于四川盆地西部,南起乐山,北至中江县,是成都市区内的一条活动性断裂带。区域上属于扬子板块,是次级构造单元川西盆地与川中隆起的界线,总体走向呈NE20°~30°,总长大于230km。龙泉山断裂带主要由分布于龙泉山背斜东西两翼的东坡断裂和西坡断裂组成。其中西坡断裂由一系列倾向南东的逆冲断层组成,龙泉山背斜发育在龙泉山西缘逆断裂带的上盘,呈西陡东缓的断裂扩展背斜展布;东坡断裂为倾向北西逆冲断裂,形成了与龙门山构造带向反的构造格局。通过对龙泉山断裂带的地表地形调查可知龙泉山断裂带整体呈西边陡而东边缓,且西坡断裂的规模和断距都明显大于东坡断裂,由此认为西坡断裂是致使龙泉山背斜形成的主干断裂,而东坡断裂则是规模较大的反向断层。且西坡断裂局部具有晚更新世弱活动性,曾经发生过ML=5.5级左右的地震;东坡断裂活动性较弱,未发现可以证明第四纪以来活动性的地貌。通过对龙泉山断裂带的地震剖面解释发现龙泉山断裂带向上突破地表,向下断距逐渐减小,倾角变缓,直至消失于雷口坡组膏盐层中。且深部构造反映的褶皱形态表明,龙泉山背斜是受深部滑脱面控制的脱顶构造,龙泉山背斜形成与龙泉山断裂有密切的成因联系。虽然前人对龙泉山断裂带做了大量研究,但是对于龙泉山断裂带的形成机制还没有达成统一认识。构造物理模拟实验是研究地质构造形成机制与演化的重要手段,由此本文通过构造物理模拟实验发现龙泉山断裂带与龙门山构造带应属于同一个构造系统。龙泉山断裂带是其构造前缘部分,与由龙门山推覆带传递过来的推挤力息息相关。实验结果显示龙泉山断裂带已经过了活动最强烈的成长期,进入了相对稳定的定型期,与龙门山构造带相比较,龙泉山断裂带的变形程度和断裂活动性都远远低于龙门山构造带,由此推测龙泉山断裂带不太可能发生ML=6级以上强震。龙泉山及周边地震活动的空间分布不均匀,断裂活动对龙泉山断裂周边的地震孕发具有一定的控制作用。历史上研究区曾多次中小地震,但破坏性地震仅发生一次,表明龙泉山断裂是具有发生中强地震能力的地震构造。然而在龙泉山断裂带地表处形成了断裂传播褶皱,使得断裂的滑动量大部分由传播褶皱吸收[1],发生大地震的可能性很小,结合构造模拟实验结果认为潜在地震能力在5.5级左右。但该断裂带为一区域性断裂,做为新构造单元划分的边界之一,并且也具备发生中强地震的构造条件,所以认为其最大发震能力不超过6.5级。
[Abstract]:After Wenchuan in 2008, the study of active faults in Sichuan Basin and the evaluation of earthquake hazard have aroused widespread concern. The Longquanshan fault zone is less than 20km from Chengdu, and the region is economically developed and densely populated. The Longquanshan fault zone is located in the western part of the Sichuan basin, with Leshan in the south and Zhongjiang County in the north. It is an active fault zone in Chengdu. It belongs to the Yangtze plate. Is the boundary between the West Sichuan Basin and the Central Sichuan uplift. The overall strike is NE20 掳30 掳and the total length is more than 230 km. The Longquanshan fault zone is mainly composed of the east slope faults and the west slope faults distributed on the east and west flanks of the Longquanshan anticline, in which the west slope faults consist of a series of thrust faults inclined to the south and east. The Longquanshan anticline developed on the upper side of the reverse fault zone in the Shanxi margin of Longquan, where the spreading anticline is distributed in the west, steepness and east, the east slope fault is inclined to the north west thrust fault, the east slope is inclined to the north west thrust fault, Through the investigation of the surface topography of the Longquanshan fault zone, it can be seen that the Longquanshan fault zone is steep in the west and gentle in the east, and the scale and distance of the fault in the west slope are obviously larger than those in the east slope. It is concluded that the Xipo fault is the main fault causing the Longquanshan anticline to form, while the Dongpo fault is a large-scale reverse fault. The Xipo fault has a weak activity in the late Pleistocene and has occurred earthquakes with magnitude ML=5.5 or so. The activity of the Dongpo fault is weak, and no geomorphology can be found to prove the activity since Quaternary. Through the seismic profile interpretation of the Longquanshan fault zone, it is found that the Longquanshan fault zone breaks through the surface upward, the downward fault distance decreases gradually, and the dip angle becomes slower. The fold pattern reflected by the deep structure indicates that the Longquanshan anticline is a topping structure controlled by the deep slip surface. The formation of Longquanshan anticline is closely related to the Longquanshan fault. However, the formation mechanism of the Longquanshan fault zone has not yet reached a unified understanding. The tectonic physical simulation experiment is an important means to study the formation mechanism and evolution of geological structures. It is found in this paper that the Longquanshan fault zone belongs to the same structural system as the Longmenshan tectonic belt, and the Longquanshan fault zone is the leading part of the structure. The experimental results show that the Longquanshan fault zone has passed through the strongest active growth period and entered a relatively stable period, compared with the Longmenshan tectonic belt. The deformation degree and fault activity of the Longquanshan fault zone are far lower than that of the Longmenshan tectonic belt, so it is inferred that strong earthquakes of magnitude ML=6 are unlikely to occur in the Longquanshan fault zone. The spatial distribution of seismic activities in Longquanshan and its surrounding areas is not uniform. The fault activity has a certain controlling effect on the occurrence of earthquakes around the Longquanshan fault. In the history of the study area, there were many small and medium earthquakes, but only one destructive earthquake occurred. It shows that Longquanshan fault is an earthquake structure with moderate earthquake potential. However, the fault propagation fold is formed on the surface of Longquanshan fault zone, which makes the slip of fault absorbed mostly by propagating fold [1], and the possibility of large earthquake is very small. Combined with the result of structural simulation experiment, the potential seismic capacity is about 5.5. However, the fault zone is a regional fault, which is one of the boundaries of the new tectonic units, and also has the structural conditions for the occurrence of moderate strong earthquakes. Therefore, its maximum earthquake generating capacity is not more than 6.5 magnitude.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P315.2

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