青藏高原东北缘壳幔介质地震各向异性特征研究

发布时间：2018-04-12 07:48

本文选题：青藏高原东北缘 + 地震各向异性　；参考：《中国地震局兰州地震研究所》2017年硕士论文

【摘要】：地震各向异性是研究地球内部介质的重要内容,而剪切波分裂是研究地震各向异性一个比较直观且有效的方法。通过对不同圈层介质地震各向异性的研究,可以提取地下矿物的性质、各向异性介质内部结构和深浅部圈层的形变特征。青藏高原东北缘作为青藏块体东北部大型边界变形带,地处青藏块体、华南地块、鄂尔多斯地块和阿拉善地块的交汇处,是新构造时期以来较为活跃的地质构造单元,其内部发育了多条规模较大且活动形迹显著的断裂,如阿尔金断裂、祁连山北缘断裂和海原断裂等。研究青藏高原东北缘壳-幔地震各向异性,一方面可以讨论在青藏高原自身的地壳缩短和增厚的影响下,各向异性与区域应力场、局部构造的关系,以及青藏高原东北缘的地壳应力分布。另一方面可以探讨青藏高原东北缘深部岩石圈或软流圈的形变特征,寻求导致高原物质东流的“逃逸”通道,对解释板块运动、软流圈流动等问题具有重要意义。选取青藏高原东北缘地区数字地震台网近场小震波形资料,应用SAM剪切波分裂分析,获得了各向异性参数,分析了该区地壳介质各向异性特征。结果表明:大部分台站的优势方向明显与区域内的主压应力方向一致,呈近NE向或NEE向,表明来自印度板块和欧亚板块的NE向或NEE向的水平挤压应力控制了青藏高原东北缘中上地壳应力场。但局部区域的快剪切波偏振方向与断裂走向一致,表明各向异性具有差异性,主要是由复杂的活动构造造成。分析认为祁连山-六盘山地震带各向异性方向主要受NE向或NEE向的背景应力场的影响,甘东南及其附近区域的各向异性情况主要受区域应力和断裂活动两方面的影响,个别地区各向异性具有差异性和离散型。利用青藏高原东北缘区域数字地震台网远震波形资料,应用切向最小能量法,计算得到各个台站下方上地幔介质各向异性的分裂参数,结果表明:祁连-河西走廊区,SKS快波偏振方向呈NW-SE,与主要断裂带走向较为一致,壳-幔变形模式为垂直连贯变形;在西秦岭北缘断裂带周围,研究发现时间延迟有较大幅度变化,这可能是岩石圈变形和软流圈物质流动共同导致;在鄂尔多斯板块内,快波方向呈NW-SE方向,可能暗示青藏高原深部物质运动是分叉绕流的。青藏高原东北缘不同区域台站下方的各向异性均具有差异性,进一步证实了青藏高原东北缘地区构造变形的复杂性。
[Abstract]:Seismic anisotropy is an important part of the study of the internal media of the earth, and shear wave splitting is a more direct and effective method to study seismic anisotropy.Through the study of seismic anisotropy of different circular media, the properties of underground minerals, the internal structure of anisotropic media and the deformation characteristics of deep and shallow circles can be extracted.The northeastern margin of the Qinghai-Xizang Plateau, as a large-scale boundary deformation zone in the northeast of the Qinghai-Tibet block, is located at the intersection of the Qinghai-Tibet block, the South China block, the Ordos block and the Alashan block, and is a relatively active geological tectonic unit since the neotectonic period.There are many large and active faults, such as the Altun fault, the northern margin of Qilian Mountain and the Haiyuan fault.To study the crustal mantle seismic anisotropy in the northeastern margin of the Tibetan Plateau, on the one hand, we can discuss the relationship between the anisotropy and the regional stress field and local tectonics under the influence of crustal shortening and thickening of the Qinghai-Xizang Plateau itself.And the crustal stress distribution in the northeastern margin of Qinghai-Xizang Plateau.On the other hand, the deformation characteristics of the lithosphere or asthenosphere in the northeast margin of the Qinghai-Xizang Plateau can be discussed, and the "escape" channel leading to the eastward flow of matter in the plateau can be sought, which is of great significance to explain the plate movement and the flow of the asthenosphere.The near field small earthquake waveform data of digital seismic network in the northeastern margin of Qinghai-Xizang Plateau are selected. The anisotropic parameters are obtained by using SAM shear wave splitting analysis and the anisotropic characteristics of crustal media in this area are analyzed.The results show that the dominant direction of most stations is obviously consistent with the direction of the principal compressive stress in the region, which is near NE direction or NEE direction.It is shown that the horizontal compressive stress in NE or NEE direction from the Indian plate and Eurasian plate controls the stress field in the upper and middle crust of the northeastern margin of the Qinghai-Xizang Plateau.However, the polarization direction of local fast shear waves is consistent with the fracture strike, which indicates that anisotropy is different, mainly caused by complex active structures.It is considered that the anisotropic direction of Qilian mountain-Liupanshan seismic belt is mainly affected by the background stress field of NE or NEE direction, and the anisotropy of southeast Gansu and its adjacent areas is mainly affected by regional stress and fault activity.The anisotropy of individual regions is different and discrete.Using the remote seismic waveform data of the digital seismic network in the northeastern margin of the Qinghai-Xizang Plateau and using the tangential minimum energy method, the splitting parameters of the anisotropy of the upper mantle medium under each station are calculated.The results show that the polarization direction of SKS fast wave in Qilian Hexi Corridor is NW-SE, which is consistent with the strike of the main fault zone, and the crust mantle deformation model is vertical and coherent deformation, and around the fault zone of the northern margin of the West Qinling Mountains,It is found that the time delay varies greatly, which may be caused by both lithospheric deformation and asthenospheric mass flow, while in the Ordos plate, the fast wave direction is in the direction of NW-SE, which may imply that the deep material movement in the Qinghai-Xizang Plateau is bifurcated.The anisotropy beneath different stations in the northeastern margin of the Qinghai-Xizang Plateau is different, which further confirms the complexity of tectonic deformation in the northeastern margin of the Qinghai-Xizang Plateau.
【学位授予单位】：中国地震局兰州地震研究所
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P315.2

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