【作者】 裴顺平；

【导师】 许忠淮； 汪素云；

【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， 2002， 博士

【摘要】 本文在详细分析研究了上地幔顶部折射波层析成像技术的理论和方法及其发展历程的基础上，搜集了中国大陆及邻区的Pn和Sn到时资料，利用层析成像技术，重建了中国大陆上地幔顶部的P波和S波速度横向变化图像，并反演出P波波速的各向异性分布。 1、用91138条Pn射线的走时反演出中国大陆上地幔顶部的P波速度横向变化和各向异性分布。求得平均Pn速度为8.05km/s，速度变化从-0.29km/s(3.6％)至+0.31km/s(3.9％)。整体上中国东西部存在明显差异，西部地区速度变化以高速异常为主：① 高速异常区主要是沿青藏高原隆起区的周边分布，特别是准噶尔盆地、塔里木盆地、柴达木盆地及四川盆地都呈明显的高速，均超过8.2km/s；② 青藏高原隆起区的中部，显示出速度的低异常带；③ 位于青藏高原东南缘的川滇西部地区速度呈现低异常。 东部地区速度变化以低速异常为主：① 整个华北和东北地区，都呈现Pn低速异常，特别是华北盆地区、渤海湾和山西地堑低速异常非常明显，最小低于7.8km/s；② 华南地区整体上在平均值上下，在珠江口地区、广西中部地区、庐山地区波速略微偏低，在长江以南，珠江以北地区中部波速略微偏高。 如果不考虑Pn波速度的各向异性变化，波速横向变化的整体趋势和考虑各向异性时接近，但Pn波速度与地质构造吻合得没有考虑各向异性时好。 中国东部的波速各向异性相对要弱于西部。整体上有三处各向异性较强，同时射线较密、范围较大，即结果相对可靠的区域：① 塔里木盆地中西部地区，快波速方向呈北西方向；② 川西藏东地区，快波速方向为北西西方向；③ 鄂尔多斯地台快波方向为东西方向。 用检测板方法进行反演结果的分辨率测试，结果表明，大部分地区对速度空间变化的分辨能够达到3°×3°，各向异性分辨能够达到4°×4°，边缘地区分辨一般较差。 2、用了43646条Sn射线反演得到中国大陆上地幔顶部S波速度横向变化。求得全区Sn平均速度为4.55km/s，速度变化从-0.14km/s(-3.1％)到+0.15km/s(3.3％)。整体上中国Sn速度分布是东低西高。在中国西部，构造上相对稳定的塔里木盆地、准噶尔盆地和吐鲁番—哈密盆地，以及柴达木盆地东端、四川盆地及其南部地区，台湾海峡等是明显的高Sn速度区，鄂尔多斯地台也偏高。在中国东部，山西北部、华北盆地，渤海湾东部、郯庐断裂郯城段周围、台湾及其东部海区、等是明显的低Sn速度区，同时川滇西部、庐山地区和青藏高原北部Sn速度也偏低。用检测板测试来检验解的分辨率，结果表明在大部分地区分辨率可达4°×4°，在新疆和四川盆地射线密集区可达3°×3°。对比Pn波速度和Sn波速度就得到波速比或泊松比的空间变化。 中国大陆上地慢顶部体波速度层析成像 3、将Pn波速度和Sn波速度横向变化与地质构造对比发现，地震波速高的 地区往往是构造上比较稳定的古老盆地、地台等，而地震波速低的地区是在构造 上比较活动的张性盆地，火山活动区和岩浆岩分布区。同时地震波速厂与地壳 厚度H呈明显的线性正相关关系，与大地热流呈负相关关系，并得到三者的线 性回归方程，回归系数D V／DH换算成b V／OP？是压强）后，与上地慢岩石的 高温高压实验结果基本一致。’4、在塔里木盆地、川西藏东地区、鄂尔多斯地台、柴达木盆地东端及其它 ’ 几个各向异性较强的地区，Pn快波速的方向与最大主压应力方向有着较好的一 致性，同时与GPS测量的地壳运动速率方向也基本上一致。 另外，在 Heam TM．提供程序的基础上，对其算法进行了一点改进，将地震 延迟按慢度网格进行归类，考虑到许多地震以成群的方式出现，有很多集中分布 在某网格内的地震实际上具有相同的时间延迟，因此本文对每个慢度网格只用一 个地震延迟，这样就减少了许多未知数，从而提高了计算的稳定性、精度和效率。 同时详细分析研究了 Yao Z石等 （199）给出的用 LSQR算法作层析成像反演时 解的分辨矩阵的求法，作为算法的应用试验，本文并将其用到Pn波实际反演中， 得到迭代500次后分辨矩阵对角线元素的空间分布。分辨矩阵对角线元素的大小 和射线的疏密呈正相关关系。更多还原

【Abstract】 In this paper the author studies the theory and method of refraction tomography at uppermost mantle. The images of P- and S-wave velocity lateral variation are rebuilded at uppermost mantle beneath China continent, and anisotropy of P-wave velocities are obtained on the basis of Pn and Sn travel time data in China and adjacent area by tomography technique.1 , Travel times of 91138 Pn arrivals recorded from China and adjacent regional earthquakes are inverted in a tomographic study to map the lateral variations and anisotropy of Pn velocity of the uppermost mantle. Average P-wave velocity 8.05km/s is got and velocities vary from -0.29km/s(3.6%) to +0.31km/s(3.9%). On the whole, the velocities are different in eastern and western China. In the west, high velocities are predominant. (1) Abnormal high velocities mainly exist around Qingzang plateau, especially in Junggar, Tarim, Qaidam and Sichuan basin, velocities there are higher than 8.2 km/s. (2) Low velocities only exist in the middle of Qingzang plateau and western part of Sichuan and Yunnan region.In eastern China, low velocities are predominant. (1) The whole North-China and most northeastern China have low velocities, especially in North-China basin, Bohai bay and Shanxi rift valley, the velocities are abnormally low. The lowest velocity reaches 7.8km/s. (2) In southern China, the velocities are near average value. A little low velocities exist in the regions such as Zhujiangkou, middle of Guangxi, Lushan and so on. A little high velocities exist in the middle region lied to the south of Yangzi river and to the north of Zhujiang river. When the anisotropy is not taken into account, the obtained image almost has the same variation pattern with that when anisotropy is considered. But Pn velocities are not well consistent with geology for the former than the later.Pn anisotropy is less remarkable in eastern China than western China. In general, there are three large regions, where anisotropy is significant. In these region rays are dense, so anisotropy are credible. (1) In Tarim basin, the direction of faster velocity is oriented NW-SE. (2) In the east of Qingzang plateau and west of Sichuan basin, the direction of faster velocity is oriented NWW-SEE, (3) In erdos terra, the direction of faster velocity is oriented E-W.The resolution of Pn image eastmated by use of Checkerboard method indicates: velocity resolution reaches 3O X 3O, anisotropy resolution reaches 4O X 4O in most regions, the resolution is low in marginal region.2, The image of Sn-wave velocity lateral variation is reconstructed in Chinacontinent by tomography method using 43646 Sn rays. The average Sn velocity is 4.55km/s. the velocity perturbations vary from -0.14 km/s (-3.1%) to +0.15 km/s (3.3%). In gerneral, Sn velocities are higher in western China than in eastern China. In the west, there are some obvious high velocity regions, such as tectonically stabe Tarim, Junggar, Turpan, Hami basin and east of Qaidam basin, Sichuan basin and to its south, Taiwan Strait and so on. High velocities also exist in Erdos. In eastern China, low velocities exist in northern Shanxi, North-China basin, to the east of Bohai Bay, northern Tan-Lu fault, Taiwan and its east. In addition, the low velocities lie in western part of Sichuan and Yunnan, Lushan and northern Qingzang Plateau. The resolution of Sn velocity by Checkerboard test is 4O X 4O in most regions,and 3O X 3O in dense ray regions, such as Xinjiang and Sichuan basin. The velocity ratio or Poisson ratio variaton can be obtained by comparing Pn and Sn velocities.3 , In comparing Pn and Sn velocity variation with geology, we will find that high velocity regions always exist in old stable basin and terra, but low velocity regions lie in active extensional basin, volcano area and magmatic rock regions. Velocity variation is positively correlated with crust thickness and negatively correlated with Earth’s heatflow. The linear regression equation of velocity, crust thichness and heatflow is obtained. The regression coefficient dV/更多还原