【作者】 楼海；

【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， 2001， 博士

【摘要】 在地壳结构研究中重力学方法是一种最古老的地球物理方法。重力方法的理论已经发展的很成熟了。但随着技术的进步，重力方法在地壳结构研究中仍然发挥着重要的作用。本文对于深部构造研究中的重力学方法进行了仔细的分析和研究。对于重力方法的几个重要内容：重力资料的数据处理和反演方法，均衡理论和应用，卫星重力资料在深部构造解释中的应用等几个方面展开了讨论。在本文中对众多的数据处理方法的假设条件和地球物理意义进行了分析。提出在重力数据处理中那些地球物理意义明确，假设条件合理，计算稳定的方法最具有实用性。在对重力反问题基本公式及其多解性的讨论的基础上，提出交互模拟方法和多种资料的综合反演方法是克服重力反问题多解性的重要途径。文中给出了可以用于三维模拟反演的线性变密度四面体重力异常计算公式。为了进行地震-重力综合解释和联合反演，文中首先给出与连续速度模型一致的密度参数化方法，推导出相应的重力异常计算公式，并应用于大别山造山带的地震-重力综合解释。结果表明，综合解释对于认识三维地震层析得到的上地壳高速体的地质意义是很有帮助的。在速度与密度一致的模型参数化的基础上，本文提出了用于密度反演的地震-重力联合反演算法。算法以地震层析方法为基础，用速度-密度关系公式把地震走时残差与密度扰动联系在一起。通过联立求解走时方程和位场方程，构成地震-重力联合反演算法。实验计算表明，在速度-密度关系已知的情况下，增加地震资料的约束，可以改善重力反演的效果。在新疆西北部地区的地壳结构研究中，结合航磁资料和地热资料，对重力资料进行了多种处理和反演。得到了关于研究区地壳结构的很多信息，包括大地构造分区，盆地基底性质，大型断裂带的分布与深部构造意义，岩浆活动性，Moho面和地壳磁性层底面深度等方面的重要信息。对新疆西部地学断面的重力与航磁资料的模拟解释，给出了地壳的密度模型和磁性模型，这些模型反映地壳深部的结构和性质。为地壳深部结构的地质地球物理综合解释提供了依据。在新疆西北部地区，均衡异常显示出天山和准噶尔南缘地区没有达到重力均衡状态，而且，重力均衡作用力的方向与地壳垂直运动的方向相反，说明挤压构造作用与均衡作用相比明显占优势。重力均衡异常显示出天山山脉的均衡状态沿山脉走向方向有很大差异，表明了天山深部物质的不均匀性。同时还显示出西准噶尔与准噶尔盆地在统一的挤压构造作用下，有不同的响应。根据对新疆及其周围地区的卫星重力资料的解释，提出天山及其周围地区处于地幔对流形成的挤压沉降构造环境。天山造山带快速隆起是南北向不对称挤压作用的结果，准噶尔盆地则在挤压作用下弯曲而发生沉降，形成南部坳陷区。卫星重力资料还显示出东，西天山深部构造上的差异。卫星重力资料的解释结果与已有的地震面波反演结果及地质资料是相容的。在腾冲火山区地壳结构的研究中，对人工地震测深资料和重力资料进行了综合解释和联合反演。人工地震测深资料的二维射线追踪解释给出了从中山至自治的南北向穿过火山区的二维速度模型。速度模型显示火山区上地壳内P波速度明显偏低，中、下地壳速度略低。在腾冲至固东之间下地壳内有P4反射面，与<WP=3>其它部位明显不同。速度模型还显示龙陵断裂南北两侧地壳速度结构有较大差异，表明分属不同构造单元。地震资料的三维层析成像给出了火山区上地壳内部的P波低速体的位置和立体图像。低速体埋深约为7km。低速体不在火山区和热海地热区的正下方。参考其他地热，大地电磁，天然地震资料的解释结果，推测低速体可能代表一个岩浆囊或局部熔融体。地震层析成像显示热海地热区位于地表低速区内。地表低速区可能有断裂通道与上地壳低速区相连。可以推测热海热田中的高温热泉和沸泉是深部热流体沿断裂通道上升，与地表热水混合后形成的。重力资料与地震资料的联合反演给出腾冲火山区中下地壳内有一南北向的低密度区。这个低密度区可能是中下地壳受热膨胀，密度降低形成的。火山区地表的张性构造与中下地壳的膨胀有关。综合分析地震，重力及地质资料，对腾冲火山区地壳构造和火山喷发机制提出如下认识：火山喷发是印度板块向东俯冲造成的。俯冲板块的重熔作用在腾冲以下的上地幔中形成岩浆积累，使中下地壳受热膨胀，密度降低，产生地表的重力低异常。中下地壳受热膨胀在地表形成张性构造，同时，也为地幔岩浆上升提供通道，形成火山喷发。更多还原

【Abstract】 Gravity is one of the oldest geophysical methods. The theory of gravity methods has been fully developed. With the advancement of the technology, however, gravity methods are still playing an important role in the investigation of the crustal structure.In this thesis, the application of gravity methods for the investigation of deep structure is carefully analyzed and studied. The discussion is concentrated on such important aspects of gravity methods as: the processing and inverse methods of gravity data, the theory and application of the isostasy, and the application of the satellitic gravity data for the deep structure interpretation.For the large number of processing methods, their geophysical significances and the preconditions are analyzed. The conclusion of the analysis is that the processing methods with clear geophysical significance, reasonable precondition and mathematical stability are the most useful in the crustal structure study. Base on the discussion about potential-field inverse problem and its ambiguity, it is presented that the interactive modeling interpretation of the gravity data and integrative interpretation of multiple geophysical data are the important approaches to overcome the ambiguity of potential-field inverse problem. An analytical expression for the gravity field of tetrahedron with linearly varying density, which can be used in three-dimensional interactive modeling interpretation, is presented in this paper.To construct a seismic-gravity simultaneous inversion algorithm, a parameterization method for linearly varying density distribution is presented. This parameterization method is similar with that used in some three-dimensional seismic tomography algorithm. The analytical formal of gravity effect calculation for linearly varying density model is then deduced and used in the seismic-gravity integrative interpretation of the Dabie mountain area, The integrative interpretation shows that it is very helpful for understanding the geological significance of the high -velocity body, which was detected by the three-dimensional seismic tomography.Based upon the coincident parameterization of velocity and density, a new seismic-gravity simultaneous inversion algorithm for density distribution is presented in this thesis. The algorithm follows the seismic tomography, using the velocity-density relationship to establish the connection between the seismic travel-time residuals and the density disturbance. By solving the travel-time equations and potential-field equations simultaneously, I construct a seismic-gravity join inversion algorithm. The test with synthetic data shows that the solution of gravity inversion is improved with the constraints of seismic data, under the condition that the relationship between velocity and density is known. In the crustal structure investigation of northwestern Xinjiang area, Bouguer gravity data, along with aeromagnetic data and geothermal data, were processed and analyzed. The results reveal mach information about the crustal structure of research <WP=5>area, such as the tectonic framework, the properties of basin’s basement, the positions and deep structural significance of large-scale fracture belts, the magma activity and the depth of Moho discontinuity and the lower interface of earth’s magnetic layer. The two-dimensional interactive modeling of gravity and magnetic data gives us the density and magnetic models along the geoscience transection of western Xinjiang. These two models exhibit the structure and properties of the deep crust, and are helpful for the geological-geophysical integrative interpretation of the geoscience transection. In the northwestern Xinjiang area, the isostatic gravity anomalies show that the Tianshan mountains and the southern margin of Jumgger basin is not in a status of isostatic equilibrium. The directions of vertical movement of the crust and that of isostatic adjustment are opposite. It means that the compressive stress is mach stronger than that of the isostattic adjustment and is the predominant t更多还原