龙门山断裂带深部结构与地震特征分析

发布时间：2017-12-28 08:06

本文关键词：龙门山断裂带深部结构与地震特征分析　出处：《昆明理工大学》2016年硕士论文　论文类型：学位论文

【摘要】：龙门山断裂带位于青藏高原东缘,北起青川,经南坝、北川、映秀、宝兴至泸定附近,全长约560km,宽约30-50km,自西向东分别发育了茂县-汶川断裂(龙门山后山断裂)、北川-映秀断裂(龙门山中央断裂)、安县-灌县断裂(龙门山前山断裂)和广元-大邑(隐伏)断裂4条主干断裂。整个断裂带在地形地貌、地壳厚度、构造应力场、密度和速度等都表现出地球物理场陡变的特征。复杂的地表形态和岩性结构,使得人们至今对龙门山断裂带的深部结构缺乏全面和准确的认识。龙门山断裂带是一条地震活动带,历史上曾发生过多次大的地震,但是到目前为止,人们对龙门山断裂带地震的性质还没有统一的认识,如断层是怎样断裂并引发地震的?主震发生后余震是按什么规律发生的?是什么因素让地震停下来的?断层在发生灾难性的断裂前是否存在人类可以认识的模式或者规律等等?因此,研究并分析龙门山断裂带的深部结构和发生地震的特征是解答上述问题和理解地震机制的关键。本研究以国家科技专项《汶川地震断裂科学钻探》项目和中国地质调查局项目《龙门山构造带三维地质填图》为依托,利用人工深反射地震剖面和大震后余震序列的空间分布规律对龙门山构造带的深部结构和地震特征进行研究。通过研究分析,揭示了龙门山断裂带北、中、南三段的地壳精细结构和构造,探讨了深部结构特征与地震的关系,形成如下认识：1、安县-灌县断裂北段在平均14km深度以上产状为NW倾,倾角约为45°,在8km深处开始变缓,可能向深部延伸至滑脱面上,多表现为叠瓦状断裂构造,其下部多存在隐伏断裂；断裂带的中段整体表现为北东陡南西缓的特征并发育了多种构造类型：双重构造、台阶式断层构造、冲凹构造、三角带及花状构造；断裂带的南段在10km深度以上产状为NW倾,倾角约为50°,在4km处开始变缓,角度为250,根据断裂在剖面上的形态推测它是以低角度向深部延伸的,这种低角度的几何学特征制约着地表破裂带主要表现为纯逆冲的运动学性质。从余震分布图可以看出,发生在安县-灌县断裂北段的的地震较少,断裂距离余震密集区较远；中段断裂下方的地震数量较多,可能跟隐伏断裂的发育有关；南段绝大多数余震均分布在断裂两侧,均位于安县-灌县断裂下方。2、研究发现映秀-北川断裂的北段在平均19km深度以上为NW倾,倾角约为55°,在6km处开始变缓,向深部以低角度延伸至滑脱面上；断裂中段在17km深度以上产状为NW倾,倾角约为55°,在9km深处开始变缓,以低角度向深部延伸至滑脱面上。从余震分布上看,断裂带北段绝大多数余震均位于映秀-北川断裂两侧,密集于安县-灌县断裂与映秀-北川断裂的交汇处。揭示出映秀-北川两条测线均位于中段的余震密集区,表现为东多西少的特征,断裂下部向深部延伸时穿过余震密集区。3、揭示出汶川-茂县断裂的中段在大约10km深度以上产状为NW倾,倾角约为550,在5km深处开始变缓,角度约为35°。从余震分布上看,该断裂附近发生的地震较零星,只在中段的南西端发育了一条NW-SE向的地震带,覆盖在汶川-茂县断裂上,该处距离汶川地震的主震位置较近,这条NW-SE向的地震带可能也是汶川地震的发生激活的产物。
[Abstract]:Located in the eastern margin of the Tibetan plateau fracture zone of Longmen mountain, north of Qingchuan, the south of the dam, Beichuan, Yingxiu, Baoxing to near Luding, approximately 560km in length, 30-50km in width, from west to East were developed Maoxian Wenchuan fault (Longmen mountain fault), Beichuan Yingxiu (central Longmen mountain fracture) Anxian Guanxian fault (Longmen Hill fault) and Guangyuan Dayi (hidden) 4 faults of main faults. The whole fault zone is characterized by the geomorphic geomorphology, the thickness of the crust, the tectonic stress field, the density and the velocity of the geophysical field. The complex surface morphology and lithologic structure make people lack a comprehensive and accurate understanding of the deep structure of the Longmen mountain fault zone. The Longmen mountain fault zone is an active seismic zone, the history of the big earthquake happened many times, but so far, the nature of people with earthquakes on the Longmen Shan fault is not a unified understanding, such as how the fault rupture and trigger the mainshock aftershock earthquake? What is happening according to law is? What factors make the earthquake stopped? The fault in the presence of humans can know if the law of fracture mode or catastrophic before? Therefore, research and analysis of characteristics of the deep structure of the Longmen mountain fault zone and earthquake is the key to answer the above questions and understand the mechanism of the earthquake. Based on the national science and technology projects "Wenchuan earthquake fault Scientific Drilling Project" and Chinese geological survey project "three-dimensional geological mapping" Longmen mountain tectonic belt based on the study of the deep structure and the spatial distribution characteristics based on artificial seismic deep reflection seismic profile and large earthquake aftershock sequence of the Longmen mountain tectonic belt. Through research and analysis, reveals the fine crustal structure and tectonic three section of Longmen Mountain Fault Zone in the south, north, and discusses the relationship between structural features and deep seismic, formed as follows: 1 North, Anxian Guanxian fault in the above average depth of 14km occurrence of NW tilt angle of about 45 degrees, start slow at the depth of 8km, likely to extend to deep slip surface, more performance for the imbricate faults, the lower part is buried fault; middle fault zone for the overall performance characteristics of North East steep slow development and Nancy structural types: double step type structure, fault structure, punching concave structure, triangle belt and flower structure; the southern fault zone at 10km above the depth of occurrence of NW tilt angle of about 50 degrees, slowed at 4km, the angle is 250, according to the morphology of the fracture in the section that it is at a low angle to the deep extension of the low angle The geometric characteristics restrict the surface rupture zone to be the kinematic character of the pure thrust. See from the aftershock distribution, earthquake occurred in less northern Anxian Guanxian fault the fault distance of aftershocks dense area far below the middle fault; earthquake quantity, buried faults might be related with development; the vast majority of South Yu Zhenjun distribution along both sides of the fault, are located below the Anxian Guanxian fault. 2, the study found that the Yingxiu Beichuan fault in the northern section of 19km above the average depth of NW tilting angle of about 55 degrees, slowed at 6km, extends to depth at a low angle to the slip surface; fracture in the middle of the 17km above the depth of occurrence of NW tilt angle of about 55 degrees, start slow at the depth of 9km, at a low angle to the deep slip surface extends to. From the aftershock distribution, the northern part of the fault zone most aftershocks are located on both sides of the Yingxiu Beichuan fault, located at the intersection of dense in Anxian Guanxian fault and the Yingxiu Beichuan fault. The aftershocks reveal dense region of the Yingxiu Beichuan two lines are located in the middle of the performance characteristics of the east than in West, the lower fault extends to depth through the dense region of aftershocks. 3, it is revealed that the middle section of the Wenchuan Maoxian fault is NW inclined at about 10km depth, and the dip angle is about 550, and it begins to slow down in the depth of 5km, and the angle is about 35 degrees. From the aftershock distribution, the occurrence of the fault near the earthquake are scattered, only in the middle of the south west developed a NW-SE to the earthquake zone, covering in Wenchuan - Maoxian fault, the distance of the Wenchuan earthquake occurred near the main shock location, activation of the product of the NW-SE to the earthquake zone may also be Wenchuan earthquake the.
【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：P315.2

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