【作者】 黄建平；

【导师】 倪四道； 傅容珊；

【作者基本信息】 中国科学技术大学 ， 固体地球物理， 2008， 博士

【摘要】 地球内部界面的研究,对于我们认识地球内部结构、物质组成、各圈层演化的动力学过程都有着十分重要的意义。由于地球内部的物质非均匀性、地球内部温度的异常、俯冲板块及地幔热柱的作用,使得地球内部的界面可能存在起伏。通过大量研究表明,对于地球界面起伏的研究,能够很好的将界面起伏与物质温度、地幔对流状态联系起来。本文主要采用接收函数和海洋T波来研究地球界面的起伏。对于地球内部间断面起伏的研究,我们从研究方法上的差异分为两类:第一类,界面起伏的确定性研究,本文主要采用转化波的接收函数方法。在利用接收函数方法进行界面起伏研究的时候,本文主要做了以下工作:（1）实现了共转换点叠加接收函数的方法,并通过对给定的两个较为复杂的2D模型的理论计算测试,证实了共转换点叠加方法和程序的正确性和可行性。（2）将程序发展到3D,并应用于实际区域上地幔界面起伏的研究中,得到了委内瑞拉和青藏高原地区410公里、660公里间断面的位置和起伏信息。在处理过程中,我们对接收函数的质量进行了评分,并作为后续叠加时的权重之一;同时在网格内部还引入了高斯权重因子取代传统的线性叠加算法。（3）实现了利用重力反演地壳厚度的方法,并用于计算中国地区大尺度的Moho面起伏,从另一个角度与接收函数的结果进行了对比研究。（4）通过对PKKPbc及其前驱波震相的分析,研究了外核顶部由轻元素组成的刚性薄层的地震学性质。第二类,界面起伏的统计性研究。对于界面起伏统计性研究,本文以不同尺度海底地形起伏对海洋T波激发的影响为例进行了说明。随后,本文也分析了T波与地震震源参数之间的关系,以及利用深震激发的T波来研究俯冲板块衰减特性。（A）界面起伏的确定性研究界面起伏的研究,主要是利用地震学中的前驱波震相（precursor）,比如通过对地表前驱波S₄₁₀S、S₆₆₀S、P₄₁₀P、P₆₆₀P等的研究,可以得到410公里、660公里间断面的起伏。本文的研究主要利用接收函数H-Kappa叠加及接收函数3D共转换点叠加的方法来研究地壳和上地幔界面大尺度的起伏。本文的对于大尺度地球界面的研究主要分为以下几个方面:（1）通过网格搜索可能的地壳厚度（H）和纵横波速比（Kappa）的方法,可以得到研究台站下方的地壳厚度和纵横波速比。而地壳厚度和纵横波速比信息将为区域构造、岩石性质等研究提供帮助。（2）本文实现了共转换点叠加接收函数的方法,并通过两个2D模型的理论计算测试,首先验证了方法的正确性;其次在3D的叠加过程中引入了高斯权重函数和N次方根的方法,提高了对接收函数中一致信号的拾取。最后,将此方法用于实际接收函数的处理中,得到了委内瑞拉和青藏高原地区的410公里、660公里界面的起伏。利用物质高温高压试验的克拉贝隆曲线斜率的结果,将得到的界面起伏转化为温度变化的信息,为探测俯冲板块（冷）和热点热柱（热）提供依据。（3）我们编程实现了傅容珊教授1984年提出的利用重力傅立叶迭代法及刘元龙研究员提出的压缩质面法,并反演得到了中国地区大尺度的地壳厚度分布。我们之所以进行重力方法的研究,主要是为了与上文利用接收函数方法的结果进行对比。（4）通过对PKKPbc波形及其前驱波的分析,得到了外核顶部轻元素组成的刚性薄层（CRZ）的地震学性质:我们还通过比较不同位置的前驱波到时的差异,提出了外核可能存在tangent cylinder结构的地震学证据。综上所述,我们系统地形成了从接收函数的提取、接收函数信噪比的改进、接收函数叠加成像、高温高压试验对结果解释等相关研究的一整套方法。基于本文的叠加方法,我们可以快速准确地得到地下间断面的起伏,并与物质的温度异常联系起来,从而可以用来探测地球内部俯冲板块和热点热柱的分布。随着大量台阵的架设和地震波数据的积累,本文的方法在未来的研究工作中将有很好的应用前景。利用重力资料得到Moho面起伏的方法,可以从另一个角度对接收函数的结果进行验证,希望能成为接收函数方法的一个有益补充。（B）界面起伏的统计性研究对于尺度较小界面起伏的研究,由于频率的限制,很难用确定的地震波震相去研究小尺度界面起伏,而一般进行统计学上的描述。对于小尺度界面起伏的研究,我们主要以海底地形起伏为例,讨论了不同小尺度海底地形起伏对T波激发的影响。通过测试不同的海底地形起伏的模型所对应的T波能量的大小,计算结果表明海底地形起伏对T波的激发有一定的促进作用。随后,我们也讨论了T波的可能应用,主要包括研究T波与地震震源参数的关系、利用深地震T波来研究俯冲板块的衰减特性。更多还原

【Abstract】 The interior discontinuities of the earth play an import part in the study of the earth’s interior velocity structure、mineral composition、the evolution and interaction between different layers. Affected by anisotropy caused by the mineral arrangement、temperature anomaly、subducted slab and the mantle super plume, the discontinuities of the earth can afford some topography instead of horizontal flatting. Abundant studies suggest that the topography at each discontinuity can give some information about the material temperature and the mantle convection.In this study, we use the receiver function and Oceanic T wave to study the topography of the interior discontinuities. Due to the different methods to study the topography, we separate our work into two groups: （1） the deterministic study on the topography of the discontinuities. Depending on the traditional receiver function study, we have made some improvements in the following aspects: （a） we firstly write the 2D common convection point method, and then we test the correctness and robustness for two complicate input 2D velocity models. （b） For further application, we improved the 2D code to 3D, and then use this method to study the topography of the upper mantle discontinuities beneath Venezuela and Tibet region. During the data processing, for improvement, we also introduced the gauss weight function to rate the energy from different distance convection points. Another improvement is also made by weighting the original receiver function, and this weight will be introduced to the CCP stacking procedure. （c）At last, for comparison, we have written a 3D gravity inversion method to get a large scale Moho topography result which is used to compare with the result of the receiver function. （2） The statistic study on the topography of the discontinuities.. In this study, we calculate the effect of the topography of the Oceanic bottom to the synthetic T wave generation. From synthetic test results, the topography of the Oceanic bottom plays an important part in the generation of the synthetic T wave. After that, we also study the empirical relationship between the earthquake focal mechanism and the energy of the T wave; the other work about T wave is that we use the T wave generated by deep earthquake to study the quality factor of the subducted slab.（A） The deterministic study on the topography of the discontinuitiesIt is an ordinary way to use the precursor phases to obtain the topography of the discontinuities, such as the study of the S₄₁₀S、S₆₆₀S、P₄₁₀P、P₆₆₀P can be used to study the topography of the 410 and 660Km discontinuities. In this paper, we mainly use the H-Kappa stacking receiver function method and the 3D common convection point method to study the large scale topography of the crust and upper mantle discontinuities. The main studies in this paper are as follows:（1） Utilizing the grid search H-Kappa stacking receiver function method, we obtain the thickness of the crust and the Vp/Vs ratio （Kappa） beneath the stations. Such results are useful to interpret the regional tectonic and petrology.（2）In this study, we develop the 2D Common Convection Point （CCP） stacking receiver function method to 3D. After testing the correctness and robustness of our code and method, we use the CCP stacking method to study the upper mantle discontinuities of Venezuela and Tibet region to get the topography of the 4101am 660km discontinuities. During the data process, we introduce the gauss weighting function and the Nth-root stacking method to improve the quality of the image. Benefit from the Clapeyron slope of mineral physics experiment at high temperature and high pressure, we translate our topography result of the discontinuity to the mineral temperature variation, thus our method can be used to detect the subducted slab （cold）、hotspots and plume （hot）.（3） We develop a code based on the method of Prof,Fu and Prof,Liu, and then apply this method to get the crustal thickness of the whole China region. The purpose of this study is used to give a comparison to the receiver function method.（4） By analyzing the PKKPbc and its precursor, we obtain the seismic constrain of the Core Rigidity Zone （CRZ） composed by the outer core light element at the top of the outer core. In addition, after comparing the time difference between the precursor and the main PKKPbc phase at different outer core conversion point positions, we find the seismic evidence for the tangent cylinder structure in the outer core.As a summary, in this article, we systematically present a whole method including the receiver function extraction、the receiver function signal to ratio improvement、receiver function stacking to get inner earth image、mineral physics experiment at high temperature and high pressure to interpret the topography result. Based on the upper method, we can obtain the topography of the discontinuities immediately, which is correlated with the distribution of the subducted slab and hotspots and plume. Because more and more stations and data will be available soon, the method in our article will have a bright future. Utilizing the gravity method to inverse the topography of Moho will provide another independent way to give a comparison with the receiver function method, and will hopefully be a good supplement for the receiver function.（B） The statistic study on the topography of the discontinuities.To small scale topography study, considering the frequency issue, it is hard to use a certain phase to study the small scale topography. We mainly use the statistic method to study the small scale topography of the discontinuities. In this article we mainly take the study of the effect on the small scale topography at the Oceanic bottom to the generation of the synthetic T wave as an example. After comparing the T wave energy generation by different small scale topography at the Oceanic bottom, we find the existence of the small scale topography at the Oceanic bottom plays an important part in the generation of the T wave in the SOFAR channel. Furthermore, we also give two application studies of the T wave including （1） the empirical relationship between the T wave energy and the fault mechanism parameter of the earthquakes （2） the study of the Fiji-Tonga slab quality factor from the T wave generated by deep earthquakes in this region.更多还原