地球物理学进展 ›› 2019, Vol. 34 ›› Issue (1): 48-63.doi: 10.6038/pg2019CC0534

• 固体地球物理及空间物理学(大气、行星、地球动力学、重磁电及地震学、地热学) • 上一篇    下一篇

近地表地震层析成像方法综述

张明辉1,刘有山2,侯爵2,3,4,徐涛2,5,白志明2   

  1. 1. 滨州学院, 信息工程学院, 山东滨州 256600
    2. 中国科学院地质与地球物理研究所, 岩石圈演化国家重点实验室, 北京 100029
    3. 中国科学院大学, 北京 100049
    4. 中国地震局地球物理研究所, 北京 100081
    5. 中国科学院青藏高原地球科学卓越创新中心,北京 100101
  • 收稿日期:2018-12-04 修回日期:2019-01-13 出版日期:2019-02-20 发布日期:2019-04-15
  • 作者简介:张明辉, 女, 1990年生, 博士, 讲师, 主要从事地震波成像研究. (E-main: zmhjoy@163.com)
  • 基金资助:
    国家重点研发计划“深地资源勘查开采”重点专项(2016YFC0600201);国家重点研发计划“深地资源勘查开采”重点专项(2016YFC0600101);国家重点研发计划“深地资源勘查开采”重点专项(2016YFC0600302);国家自然科学基金联合资助.(41574082);国家自然科学基金联合资助.(41874065);国家自然科学基金联合资助.(41604076);国家自然科学基金联合资助.(41804060);国家自然科学基金联合资助.(41774097)

Review of seismic tomography methods in near-surface structures reconstruction

ZHANG Ming-hui1,LIU You-shan2,HOU Jue2,3,4,XU Tao2,5,BAI Zhi-ming2   

  1. 1. Institute of Information Engineering, Binzhou University, Shandong Binzhou 256600, China
    2. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Science, Beijing 100029, China
    3. University of Chinese Academy of Sciences, Beijing 100049, China
    4. Institute of Geophysics, China Earthquake Administration, Beijing 100081, China
    5. CAS Center for Excellence in Tibetan Plateau Earth Science, Beijing 100101, China
  • Received:2018-12-04 Revised:2019-01-13 Online:2019-02-20 Published:2019-04-15

摘要:

近地表地层与人类生产生活密切相关,利用地震层析成像方法准确重建浅部地壳速度结构有助于开展高精度地震勘探、探查浅部矿产资源、规避潜在自然灾害,并利于城市地下空间建设.中国大陆地表条件复杂,尤其中西部盆岭结合带地形起伏剧烈,对浅部地壳精确速度建模构成严重挑战.本文系统论述了地震层析成像领域基于高频近似理论的走时成像方法和有限频层析成像方法,阐明两类方法的基本原理、存在问题和发展方向等.依据正演走时有无显式射线追踪,基于高频近似理论的走时成像方法分为传统走时层析成像方法和无射线路径的走时层析成像方法.基于射线追踪的传统走时层析成像方法,在浅层速度强烈变化时,因存在阴影区或多路径现象引起成像失真,严重影响成像效率;而无射线路径的层析成像方法通过程函方程走时场的正传和逆传直接计算敏感核,并利用伴随状态法获得目标函数的梯度,具有快速、稳健的优点.以上两种基于地震射线高频近似理论的走时成像方法由于未考虑地震波频率的带限性,存在波散射、波前愈合及反演约束差等问题.有限频层析成像方法克服了射线理论“无限高频”假设所带来的弊端,已成为重要的研究方向之一.该类方法主要分为射线有限频层析成像方法和基于波动方程的有限频层析成像方法.射线有限频层析成像方法能够提高成像的分辨率,但在方法本质上仍依赖于射线理论,较难处理较复杂的波现象问题;基于波动方程的有限频层析成像方法能准确处理复杂地质问题,提高成像可靠性并能以图像形式直观展示地球内部地震波的速度结构分布,但是该方法在实际应用中强烈依赖于数据中的低频信息及较精确的初始速度模型,其推广应用仍需进一步探索.

关键词: 近地表, 地震层析成像, 高频近似, 有限频, 波动方程

Abstract:

The near-surface crustal structure is closely related to human production and life. Accurate reconstruction of the velocity structure of shallow crust by seismic tomography can help us to carry out high-precision seismic exploration, explore shallow resources and minerals, avoid potential natural disasters, and construct urban underground space. Complex surface conditions are widely found in China mainland, especially in the basin-range junction zone of central and western China, which poses a serious challenge to accurately reconstruct the velocity model of shallow crust. This paper discusses systematically the basic principle, existing problems and development direction of two types of current seismic tomography methods, namely, traveltime tomography method based on high frequency approximation theory and on the finite frequency tomography theory. The former is based on the high-frequency approximation theory of seismic rays. According to whether there is explicit ray tracing in the forward calculation, it can be divided into the conventional traveltime tomography method and the traveltime tomography method without ray paths. The conventional traveltime tomography method utilizes the traditional ray tracing methods. When the near-surface velocity changes strongly, the imaging distortion is usually caused by the existence of shadow zone or multi-paths, which seriously affects the imaging efficiency. While, the traveltime tomography method without ray paths calculates the sensitive kernel directly by forward and backward propagation of the traveltime field of the eikonal equation, and obtains the gradient of the objective function by the adjoint state method, which has the advantages of fast and robustness. Since the band-limited property of the seismic wave frequency is not considered, there are some problems of the traveltime tomography based on high frequency approximation theory, such as wave scattering, wave front healing and poor inversion constraint. The latter, that is, the finite frequency tomography overcomes the drawbacks of the assumption of “infinite high frequency” in ray theory and has become more important. The methods are mainly divided into ray finite frequency tomography method and the finite frequency tomography method based on wave equation. Ray finite frequency tomography can improve the resolution of imaging, but in essence, it still depends on ray theory and is difficult to deal with complex wave phenomena. The finite frequency tomography method based on wave equation can accurately deal with complex geological problems, improve imaging reliability and visually display the velocity structure of seismic waves in the earth’s interior in the form of images. However, this method strongly depends on sufficient low-frequency information in data or a more accurate initial velocity model in practical applications, and its wide application requires further exploration and development.

Key words: Near-surface, Seismic tomography, High frequency approximation, Finite frequency, Wave equation

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