【作者】 周小仙；

【导师】 钱荣毅；

【作者基本信息】 中国地质大学（北京） ， 地球探测与信息技术， 2010， 硕士

【摘要】 地震层析成像就是用地震数据来反演地下结构的物质属性,并逐层剖析绘制其图像的技术。其主要目的是确定地球内部的精细结构和局部不均匀性(杨文采,1993)。该技术最初是从医学CT理论发展而来的,随着其在地学上的研究不断发展和深入,已经取得了丰硕的成果,因而被越来越多的人接受和推广。地震层析成像按射线追踪时所用的地震波资料的不同可分为透射波层析、反射波层析、折射波层析、面波层析等。其中透射波层析研究的最为成熟,主要以跨井方式进行观测;其次是折射波层析,其优势在于利用了大偏移距的信息,主要致力于求取近地表风化层的速度和厚度;反射波层析的研究最难,因此最不成熟,虽然其研究范围比折射波层析要深,但是反射波层析受到有限观测角小等问题的影响,因此层析精度不高。为了提高层析成像精度,人们开始将两种以上的地震波资料联合起来进行层析成像研究。本文首先简述了地震层析成像发展历史及基本原理,分析研究了各种射线追踪和反演算法的优缺点,并将折射层析方程组和反射层析方程组联立起来,进行旅行时联合层析成像。由于综合利用了折射波和反射波的信息,联合层析成像扩大了有限观测角,增加了射线密度,因此理论上其精度要比单一的折射层析或反射层析的精度高。然后本文对Jun Korenaga的折射和反射联合层析成像软件中的网格节点设置方式进行了改进,并进行了两个模型的数值模拟以及一个不同尺度模型的对比试验,模拟结果表明改进后的软件的反演效果有所提高并且广角地震数据比其他数据的层析反演效果好;对比试验结果表明对中等尺度(排列长度几公里以上)及以上的地震数据进行联合层析成像的效果比小尺度(排列长度几公里以内)的地震数据的效果好得多。更多还原

【Abstract】 Seismic tomography is a technique which deduces and draws the physical properties of underground structure from the inversion of seismic data. Its main purpose is to determine the fine structure of the Earth’s interior and local inhormogeneity ( Wencai Yang, 1993 ). Tomography is originally used in medical research. With the increasing development of geological tomography, the research on geological tomography has achieved great successes and received increasing acceptability and expansion.According to the differences in the used seismic data, seismic tomography can fall into four types-transmission tomography, reflection tomography, refraction tomography and surface wave tomography. Transmission tomography, which conducts observation in cross-wells, is studied deeper than the other types. It is followed by refraction tomography, of which the advantage is that it utilizes long offset records. Research on reflection tomography is far away from maturity. Although reflection tomography studies deeper subsurface structure than refraction tomography does, it has lower inversion accuracy. In order to improve the inversion accuracy of seismic tomography, researchers begin to carry out simultaneous inversion of two or more types of seismic data.This paper outlines the development and the basic principles of seismic tomography, and analyzes the advantages and disadvantages of various ray tracing methods and inversion algorithms. This paper also deduces simultaneous tomography equation from reflection tomography equation and refraction tomography equation. The inversion accuracy of simultaneous tomography, in theory, can be improved, since it utilizes both reflection data and refraction data and this combination can increase observation angle. Then this paper improves the distribution of grid nodes in Jun Korenaga’s joint reflection and refraction tomography program, and then carries out numerical simulation with two models. The results show that the improved program has higher inversion accuracy and simultaneous tomography with wide-angle seismic data has better results than other kinds of seismic data. In addition, a comparison experiment is conducted and its result shows that seismic data of intermediate scale and large scale (the length of seismic arrangement is more than several kilometers) is more appropriate for simultaneous tomography than small scale data (the length of seismic arrangement is less than several kilometers).更多还原