用地震震源机制和各向异性研究青藏高原东缘动力学特征

发布时间：2018-03-08 12:37

本文选题：青藏高原　切入点：接收函数　出处：《成都理工大学》2017年博士论文　论文类型：学位论文

【摘要】：青藏高原的隆升和扩张在长期以来一直是地球科学界的热点问题之一。科学家们提出了许多不同的模型来解释青藏高原的变形机制,而近年来刚性地壳块体沿大型走滑断层的侧向挤出与中下地壳的粘性物质管道流则是争论的焦点。刚性地壳模型认为断层扮演了关键角色,而下地壳流模型认为下地壳从上地壳和上地幔解耦。本文搜集了四川地震台网记录的龙门山断裂带2008-2014年3级以上的地震波形资料,通过矩张量反演获取了1491个地震震源机制解。此外,本文还搜集了研究区内在龙门山地区以外发生的695个地震震源机制解。根据震源机制解的断层面参数,本文采用阻尼线性反演技术获取了研究区内高分辨率的构造应力场。同时,本文搜集了研究区内密集的宽频带流动台站记录的地震波形资料,分别采用接收函数集分析和SKS/SKKS分裂测量对青藏高原东缘地壳和上地幔各向异性进行了研究,并且采用接收函数叠加扫描技术,研究了青藏高原东缘的地壳厚度和地壳平均波速比。(1)研究区内上地壳构造应力场呈现区域性分布。在龙门山断裂带,应力方向不仅呈现出分段分布特征,而且在龙门山断裂带的前山断裂、中央断裂和后山断裂也不尽相同。此外,应力方向在龙门山断裂带的不连续变化可能反映了龙门山断裂带不是协调运动的。在龙门山以外地区,应力方向呈现出简单清晰的区域性变化特征。川滇菱形块体内部与其东边界的鲜水河-安宁河断裂带的最大压应力方向不同,安宁河断裂带以东及四川盆地以南地区,最大压应力的方向又有所变化。最小压应力在整个青藏高原东缘呈现出比较连续的变化,但是在龙门山断裂带显示出复杂的分布特征。对汶川-芦山地震空区构造应力场的研究发现,最大压应力在18公里上下发生明显变化,可能反映了地壳在该深度上下为解耦变形。(2)通过接收函数集分析研究地壳各向异性,各向异性的快波方向没有显示出块体分布特征,在整个青藏高原东缘呈现复杂的变化特征。松潘-甘孜块体的快波方向以SE方向为主,与上地壳构造应力场的近W-E方向存在明显差异。在川滇菱形块体内,快波方向转为基本呈SEE或SWW向。在鲜水河断裂带附近,快波方向基本与鲜水河断裂带走向平行。在四川盆地及以南地区,快波方向主要为NE或NEE向。时间延迟分布在0.1-1秒范围内,平均时间延迟为0.41秒。在龙门山断裂带、鲜水河断裂带和安宁河断裂带的接合处,时间延迟显著增大。(3)采用SKS/SKKS分裂测量研究上地幔各向异性,平均时间延迟为1.2秒,显著高于地壳0.41秒的平均时间延迟。在松潘-甘孜块体内,快波方向主要为SSE向。而向东跨过龙门山断裂带进入四川盆地,快波方向以SE向为主导。龙门山断裂带南段的快波方向呈现两种特征,一种是与安宁河断裂带走向相平行的NNE向,另一种与四川盆地NE向的快波偏振方向相一致。四川盆地以南地区,快波方向与四川盆地基本一致。鲜水河-安宁河断裂带的快波方向基本与断裂带走向平行。在川滇菱形块体内,快波方向呈现非常复杂的分布,这可能反映了该块体内复杂的变形机制,以及块体内的上地幔存在不连续变形。(4)研究区内的地壳厚度呈现区域性分布特征,但并不完全以区内大型断裂为界。地壳厚度在龙门山断裂带约为45公里左右,从汶川地震向南开始增厚,地壳厚度增厚至约50公里。在松潘-甘孜块体的东北部,地壳厚度基本稳定在48-54公里范围内,但在松潘-甘孜块体南部,地壳厚度为54-64公里,与川滇菱形块体显示出相同的分布特征。安宁河断裂带及四川盆地以南的地区,地壳厚度基本在54公里以内,与川滇菱形块体呈现明显对比。由此可见,鲜水河断裂带虽然是松潘-甘孜块体与川滇菱形块体在地表构造上的边界,但并没有构成两者在深部构造上的边界。而安宁河断裂带不仅是川滇菱形块体与扬子板块的地表构造边界,也是深部构造上的边界。(5)高波速比值主要分布在鲜水河-安宁河断裂带及周边地区,可能反映了这些地区具有软弱的中下地壳。四川盆地内部分地区波速比值可达1.8左右,特别是在龙泉断裂一带,可能是由于盆地内普遍存在厚度约为6-10公里沉积层。在松潘-甘孜块体和川滇菱形块体内部,绝大部分地区的地壳平均波速比在1.75左右,显示了中等变形强度。(6)研究区内绝大部分地区的地表GPS速度、最大压应力和地壳各向异性与上地幔各向异性之间均存在明显差异,发现了研究区内地壳内以及壳幔间普遍存在的解耦运动。因此这个事实可以排除垂直连贯变形的可能性,同时为青藏高原东缘的深部变形机制为分层变形提供证据。本文认为,青藏高原东缘内普遍存在低速的下地壳,表现为下地壳滑脱层,相对高速的上地壳在滑脱层上发生远距离运移,这是青藏高原东缘的主要变形模式。
[Abstract]:The uplift of the Tibetan Plateau and expansion in the long term is one of the hot issues of earth science. Scientists have proposed many different models to explain the mechanism of deformation of the Tibetan Plateau, and in recent years the rigid crust along the large lateral strike slip faults extrusion viscous material pipeline and the lower crustal flow is the focus of debate rigid crust model fault that played a key role, while the lower crustal flow model that the lower crust from the upper crust and upper mantle decoupling. This paper collects the Longmen Mountain Fault of Sichuan seismic network with 2008-2014 years of more than 3 seismic waveform data, the moment tensor inversion 1491 earthquake focal mechanism solutions are obtained. In addition in this paper, also collected outside the study area in Longmen mountain region 695 earthquake focal mechanism solution. According to the focal mechanism solution of the fault plane parameters, this paper uses damped linear inversion The technology to obtain high resolution tectonic stress field in the study area. At the same time, this paper collected in the study area with dense broadband seismic waveform data recorded by the stations, respectively in receiver function analysis and SKS/SKKS splitting measurement on the eastern margin of the Tibetan Plateau and the crust and upper mantle anisotropy were studied, and the receiving functions. Study on the scanning technology, the eastern margin of the Tibetan Plateau the crust thickness and the average crustal velocity ratio. (1) in the study area on the crustal stress field showed the regional distribution in the Longmen Mountain Fault Zone, the stress direction not only showing sectional distribution, but also in the Longmen Mountain Fault Zone mountain front fault, central fracture and mountain fault are not the same. In addition, the stress in the direction of the Longmen Mountain Fault Zone discontinuous changes may reflect the Longmen mountain fault zone is not coordinated movement. In the area of Longmen mountain, the direction of stress Presents a simple and clear regional variations. The maximum pressure of Sichuan Yunnan block inside and east boundary of Xianshuihe ANNINGHE FAULT ZONE stress in different directions, east of the Anning River fault zone and Sichuan basin area to the south, the maximum compressive stress and the direction of change. The minimum stress shows change is continuous at the Eastern margin of the Tibetan Plateau, but in the Longmen mountain fault zone shows the distribution characteristics of the complex. The structure of Wenchuan - Lushan earthquake stress field of the gob area, the maximum compressive stress changes obviously in 18 kilometers, may reflect in the depth of crust for decoupling deformation. (2) by receiving the function set analysis of crustal anisotropy, fast wave direction anisotropy shows no block distribution, showing the complex characteristics in the eastern margin of the Qinghai Tibet Plateau. The Songpan - Ganzi block the fast direction by SE The main difference in W-E direction stress field of upper crust. In the Sichuan Yunnan rhombic block, fast direction to basic is SEE or SWW. In the vicinity of the Xianshuihe fault zone, with the fast direction parallel to the Xianshuihe fault zone. In the Sichuan basin and the south area. Fast direction is NE or NEE. The time delay distribution in 0.1- second range, the average delay time of 0.41 seconds. In the Longmen Mountain Fault Zone, joining the Xianshuihe fault zone and the Anning River fault zone, the time delay increases significantly. (3) the SKS/SKKS splitting measurement of upper mantle anisotropy, average time delay of 1.2 seconds, the average time was significantly higher than that of the crust 0.41 seconds delay. In the Songpan - Ganzi block, fast direction is mainly SSE. And to the east across the Longmen Mountain Fault Zone in Sichuan basin, with SE as the leading to the fast direction. The fast fracture zone of Longmen mountain south section The direction has two characteristics, one is NNE and ANNINGHE FAULT ZONE to parallel, consistent with another NE of the Sichuan basin to the polarization direction of fast wave. The area south of Sichuan basin, Sichuan basin and the fast direction is consistent. With the fast direction of Xianshuihe ANNINGHE FAULT and fracture in parallel with the strike. The Sichuan Yunnan rhombic block, fast direction distributes very complex, which may reflect the block complex deformation mechanism, and the block of the upper mantle is a discontinuous deformation. (4) in the study area, the crustal thickness showed the regional distribution characteristics, but not entirely in large fault in the area for the sector. The thickness of the crust in the Longmen mountain fault zone is about 45 kilometers from the Wenchuan earthquake to the South began to thicken, the crust thickness to about 50 km. In the Songpan - Ganzi block to the northeast, the crustal thickness is basically stable in the range of 48-54 km But in Songpan, the southern Ganzi block, the crustal thickness of 54-64 km, with the same distribution of Sichuan Yunnan block shows. Anning River fault zone and Sichuan basin to the south of the region, the crustal thickness basically in 54 kilometers, obviously compared with the Sichuan Yunnan block. Thus, fresh river fault zone is the boundary of Songpan Ganzi block and the Sichuan Yunnan rhombic block on the surface of structure, but does not constitute both in the deep structure of the boundary. The Anninghe fault zone is not only the Sichuan Yunnan rhombic block body surface tectonic boundary and the Yangtze plate, and the deep structure of the boundary Gao Bo. (5) ratio of the main distribution zone and surrounding areas in the Xianshuihe ANNINGHE FAULT, may reflect these areas with a weak lower crust in the Sichuan basin. Parts of velocity ratio can reach about 1.8, especially in the vicinity of the Longquan fault, may be due to the basin In common about 6-10 kilometers thick sedimentary layer. In Songpan Ganzi block and the Sichuan Yunnan rhombic block, the vast majority of crustal average wave velocity ratio at around 1.75, showing moderate deformation strength. (6) in the study area in most regions of the surface of GPS speed, the maximum compressive stress was significant the difference between the force and the crustal anisotropy and mantle anisotropy, found the crust in the study area and prevailing between crust and mantle decoupling motion. Therefore this fact can exclude the possibility of vertically coherent deformation, and deep into the eastern margin of the Tibetan Plateau deformation mechanism so as to provide evidence for the layered deformation. This paper argues that the widespread presence of crust of the eastern margin of the Tibetan Plateau, showed lower crustal detachment layer, the upper crust in the relatively high speed on the long-distance transport detachment layer, which is the main deformation mode of the eastern margin of the Tibetan Plateau.

【学位授予单位】：成都理工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P315.2

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