【作者】 赵启光；

【导师】 楼海；

【作者基本信息】 中国地震局地球物理研究所 ， 固体地球物理学， 2011， 硕士

【摘要】 本文对地震层析成像的理论与方法进行了较为系统地介绍,并且对FMTOMO层析成像软件所使用的多级快速行进正演算法与子空间反演算法进行了详细地阐述。本论文研究目标为青藏高原东缘深部速度结构,研究区域为98°E-108°E,26°N-34°N,深度范围为0-300km。利用9194个远震P波走时差,使用FMTOMO层析成像软件获得该区域3维P波速度结构。并结合该地区已有地球物理研究结果,对这一区域3维P波速度结构进行研究,得到以下主要认识：在60-140km深度速度扰动水平剖面图中可以看出,包含四川盆地在内的川中块体速度相对较高,川青块体以及川滇菱形块体的速度相对较低。龙门山断裂带为低速的川青块体与高速的川中块体的速度分界线,安宁河断裂带为低速的川滇菱形块体与高速的川中块体的分界线。鲜水河断裂带是川滇菱形块体与川青块体两个低速区域的分界线。60-140kmm深度范围内,102°E-104°E、29°N-31°N,四川盆地西南部区域存在一个相对低速的区域。造成这一现象的原因可能为：在下地壳至上地幔的深度范围内,由于青藏高原物质东流作用,东流的较软物质在龙门山断裂带附近遇到了坚硬的四川盆地的阻挡,部分东流物质由于阻挡作用,沿着东南方向以及西北方向流动,但是仍有部分的较软物质侵入到坚硬的四川盆地的西南部区域,造成该区域存在速度较低的现象。在60-140kmm深度范围内,沿龙门山断裂带,在龙门山断裂带的西北侧,出现相对高速的现象。造成这一现象的可能原因为：在下地壳至上地幔的深度范围内,较软的青藏高原东流物质同样由于遇到坚硬的四川盆地的阻挡作用,此部分较软的物质沿着坚硬四川盆地的边缘发生了斜上方的逆冲运动,所以在此深度范围内出现了相对高速区域。在190-290km深度范围内,青藏高原东缘地区西南区域存在着高速区域,龙门山断裂带、安宁河断裂带不再是高低速区域的分界带。在沿30.5°N速度扰动垂直剖面中,四川盆地的高速度区域延伸至大概200km深度处,可以说明坚硬的四川盆地岩石圈可能延伸至上地幔200km深度左右。在沿101.5°E速度扰动垂直剖面图中,整个川西高原地区在下地壳至上地幔的范围内表现为低速区域。这一结果也在一定程度上证明川西高原在这个深度范围内存在较软物质的可能性。更多还原

【Abstract】 The theory and the methods of seismic tomography have been introduced systematically, as well as the multistage fast marching method and the subspace inversion algorithm which are used in the FMTOMO seismic tomography software have been elaborated in this thesis.The research aim of the thesis is the deep velocity structure in the eastern edge of Tibetan plateau within the study region of 98°E-108°E,26°N-34°N,0-300km depth. The 3-D P-wave velocity structure has been obtained by using 9194 teleseismic P-wave traveltime residuals data and the FMTOMO seismic tomography software. And then, several results have been got:By observing the horizontal slice of P-wave velocity perturbation from 60km to 140km depth, the P-wave velocity of Mid-Sichuan Block is relative high, while the P-wave velocity of Sichuan-Qinghai Block and Sichuan-Yunnan Diamond Block is relative low. The Longmenshan Fault is the velocity boundary between the Sichuan-Qinghai Block with lower velocity and Mid-Sichuan Block with higher velocity. The lower velocity region of the Sichuan-Yunnan Diamond Block and the higher velocity region of the Mid-Sichuan Block are divided by the Anninghe Fault.From 60km to 140km,102°E-104°E,29°N-31°N, There is lower velocity region in the southwest of Sichuan basin. The possible explanation of this phenomenon is that: From the lower crust to the upper mantle, because of effect of east flow in the Tibetan plateau, when east flow soft material has met the block of hard Sichuan basin nearby the Longmenshan fault, some of the soft materials flow along the southeast direction as well as northwest direction, but a part of soft materials invade the southwest region of the hard Sichuan basin, which created the low P-wave velocity phenomenon.There is a relative high velocity phenomenon along the northwest side of Longmenshan fault in depth range from 60km to 140km. The possible explanation of this phenomenon is that:From the crust to the upper mantle, because of the soft materials which flow east met the impediment function of hard Sichuan basin, a part of soft materials had the thrust movement along the hard Sichuan basin edge. Therefore the relatively high velocity region appeared in this depth range.In the depth range from 190km to 290km, there is a high velocity area in the southwest region of eastern edge of Tibetan plateau. Longmenshan Fault and Anninghe Fault are not the boundary between high velocity region and low velocity region.In the image of vertical slice of P-wave velocity perturbation alone the 30.5°N, the high velocity of Sichuan basin extents to about 200km depth, which means the hard lithosphere of Sichuan basin may extent to this depth.In the image of vertical slice of P-wave velocity perturbation alone the 101.5°E, The entire west Sichuan plateau area is low velocity region in the depth range from lower crust to upper mantle, which also proves that soft materials may exist in the western Sichuan plateau in this depth range.更多还原