| 模型扩展和地形平化起伏地形处理方案在地震走时层析成像中的对比研究 |
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| 引用本文： | 郭高山,兰海强,陈凌.模型扩展和地形平化起伏地形处理方案在地震走时层析成像中的对比研究[J].地球物理学报,2019,62(5):1704-1715. |
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| 作者姓名： | 郭高山 兰海强 陈凌 |
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| 作者单位： | 1. 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;2. 中国科学院大学, 北京 100049;3. 中国科学院青藏高原地球科学卓越创新中心, 北京 100101 |
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| 基金项目： | 国家自然科学基金（NSFC41674095），岩石圈演化国家重点实验室自主研究课题（SKL-YT201802，SKL-Z201704-11712180）和中科院青年创新促进会（2015051）共同资助. |
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| 摘 要： | 中国大陆中西部普遍具有强烈的地形起伏,起伏地形会对地震资料的处理分析产生严重干扰.精细处理起伏地形成为高精度地震成像的必然要求.传统方法通过填充低速介质将不规则模型扩展为规则模型来处理起伏地形.近年来,借助坐标变换将物理空间不规则模型转换为计算空间规则模型的地形平化方法,为解决起伏地形问题提供了新思路.本文基于经典的模型扩展和新发展的地形平化方法分别处理起伏地形,从走时正演、射线追踪和反演成像三个方面,全面细致地评判了两种地形处理方法在起伏地形层析成像中的适用性和有效性.结果表明,模型扩展中阶梯状近似和填充介质速度参与计算,会造成起伏地形走时计算精度损失,出现虚假射线路径和错误出射角,导致反演分辨率降低,成像结果模糊甚至失真;地形平化中采用贴体网格参数化,能够保证离散模型完全匹配起伏地形,并且保持起伏地形在物理空间和计算空间中均为自由表面.在此基础上发展的层析成像技术具有高度的保真性,有效地处理了地形起伏效应,为起伏地形区域精细速度成像提供了有力的技术保障.
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| 关 键 词： | 模型扩展 地形平化 起伏地形 层析成像 |
| 收稿时间： | 2018-02-12 |
A comparative study of both model expansion and topography flatten in topography handling in seismic traveltime tomography |
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| GUO GaoShan,LAN HaiQiang,CHEN Ling.A comparative study of both model expansion and topography flatten in topography handling in seismic traveltime tomography[J].Chinese Journal of Geophysics,2019,62(5):1704-1715. |
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| Authors: | GUO GaoShan LAN HaiQiang CHEN Ling |
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| Institution: | 1. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. University of the Chinese Academy of Sciences, Beijing 100049, China;3. Chinese Academy of Sciences Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China |
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| Abstract: | Irregular surfaces are common situations in seismic exploration, especially at regions of middle and western China, making seismic processing and interpretation rather difficult in both oil/gas reservoir surveys and deep seismic soundings. The fine treatment of irregular topography becomes an inevitable requirement in high-precision seismic imaging. Traditionally, the problem of irregular topography is usually settled by model expansion scheme, in which the topography is regarded as an inner discontinuity after adding a low-velocity layer above the surface to expand an irregular physical space to a regular computational space. In recent years, a new method called topography flatten scheme, which involves the transformation between Cartesian and curvilinear coordinate systems, has been proposed to provide an alternative way to deal with rugged surfaces. In this paper, the both treatment schemes for irregular surfaces are briefly summarized. Then, a series of comparative tests are performed to comprehensively evaluate the accuracy, effectiveness and applicability of both methods from the first-arrival traveltimes, raypaths and imaging results of different synthetic models. These experiments indicate that the transition from a free surface to an inner discontinuity and the use of low-velocity media in model expansion scheme will cause many undesirable problems, such as loss of accuracy in calculating traveltimes and physically unrealistic seismic rays or spurious take-off angles, which can reduce seismic resolution and distort or smear structural images. For topography flatten scheme, the body-conforming grid can completely describe rugged surfaces and the topography-dependent eikonal equation (TDEE) is capable of exactly charactering the travel-time fields under complex surfaces, which establish a firm foundation for seismic imaging free from the effect of irregular surfaces. Therefore, we believe that topography flatten scheme has an exciting potential application in reconstructing high-quality seismic structures under complex topographical conditions. |
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| Keywords: | Model expansion scheme Topography flatten scheme Irregular topography Seismic tomography |
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