大华北及其邻区地壳上地幔三维速度结构的地震层析成像研究

【作者】 王志铄；

【导师】 王椿镛；

【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， 2005， 博士

【摘要】 本文对地球物理反演的发展历史和研究现状作了简单回顾,交待了大华北及其邻区的构造环境,阐述了本文所采用的反演方法的基本原理,分析了资料的可靠性和准确性,选择了适当的反演模型,得出了较好的反演结果,并对本地区的反演分辨率进行了讨论。 本文的研究区域是大华北及其邻区(107°E-124°E,28°N-42°N),即通常所指的大华北地区及其以南部分地区。这个区域是我国地震活动强烈的地区之一,曾多次发生强烈破坏性地震,区内既有大陆内部的碰撞造山带(秦岭-大别造山带),又有贯通本区南北的大型断裂带(郯庐断裂带)和大型重力梯级带(太行山),地质构造十分复杂。 本文利用区域地震到时资料、部分人工地震资料和远震的P波资料,使用赵大鹏博士提供的程序,用体波地震成像技术重建了本地区地壳上地幔的三维速度结构。对所使用的资料的可靠性作了充分的分析,对资料在本地区的层析成像分辨能力作了比较,使用了适合本次工作的分辨率0.5°×0.5°,反演出了与区域大地构造相对应的较好的结果。 本文利用大华北及其邻区475个地震台站的区域地震资料(共15714个区域地震,P波震相114971个,S波震相102142个)、三条人工地震剖面初至P波走时数据(江苏8401,山东8509,大别山9511,共51炮的数据)和4975个远震(76620个远震P波)资料。以水平方向0.5°×0.5°,垂直方向以1km、10km、25km、42km、60km为间隔划分网格,并建立初始三维速度模型。用近似弯曲射线追踪方法计算走时和射线路径,用LSQR算法进行反演。在反演之前,用检测方法分析了所用地震资料的层析成像分辨率。层析成像结果较好地反映了本地区的地壳上地幔速度结构特征。 结果表明: (1) 使用区域地震资料、远震资料和人工地震资料联合进行层析成像能够取得好的结果。 (2) 大华北及其邻区大的构造如燕山构造带、太行山前构造带、汾渭构造带、郯庐断裂带及秦岭-大别构造带等都与该区地壳上地幔的低速或高、低速度相邻的部位相对应,华北断块与扬子断块速度异常沿秦岭-大别碰撞带存在明显的分区特征,扬子断块波速异常较少,没有明显的横向不均匀性,而华北断块多更多还原

【Abstract】 The history of geophysical inversion and seismic tomography is reviewed in this paper. The tectonic of study region and the method of inversion are explained simply also. In order to get good result, the reliability and preciseness of the seismic data are analyzed carefully and the good inversion model is selected. The resolving power in this area is discussed in the end.The research region of this dissertation is 107°E-124°E and 28°N-42°N. In China geological and tectonic map, this region is referred to as the North China and some south area of it. This region is located in a seismically very active region in China. A lot of large earthquakes have occurred in it. The present study area includes many active tectonics such as Yanshan uplift, Qinling-Dabie uplift, the fault in Taihangshan piedmont, Tanlu fault ect.In total, 114971 P arrival times, 102142 S arrival times from 15714 local earthquakes, 76620 P arrive times from 4975 teleseismic events and some data from seismic sounding profile have been collected. A detailed three-dimensional(3-D) velocity model of the crust and uppermost mantle under the region is determined with a spatial resolution of 0.5° by 0.5° in the horizontal direction and 9-20 kilometer in depth. To analyze the arrival time data, we have used the tomographic method of Zhao et al.(1992). This method is adaptable to a velocity structure which includes several complex-shaped velocity discontinuities and allows 3-D velocity variations everywhere in the model. The discontinuities represent known geological boundaries, like the Moho discontinuity. A 3-D grid net is set up in model to express the 3-D structure. The tomograhic inversion was calculated using this program. According to the data distribution and several check-board tests, reliable inversion results are obtained for a model with grid size of 0.5° by 0.5° in the horizontal directions and 5 layers of 1,10,25,42 and 60 km deep from the surface to 60 km in the depth.The tomographic inversion results show that: Yanshan uplift, Qinling-Dabie uplift, the fault in Taihangshan piedmont, Tanlu fault etc are corresponding with low velocity or between low and high velocity in the crust and uppermost mantle in this region. Depth around 300 kilometer strong P-wave velocity variations of up to 4% are found in some area such as Yanshan uplift and Qinling-Dabie uplift, indicating the更多还原