Towards the geological parametrization of seismic tomography
Towards the geological parametrization of seismic tomography
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DOI：
10.1093/gji/ggad140
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发表时间：
2023-03
影响因子：
2.8
通讯作者：
V. Tsai;C. Huber;C. Dalton
中科院分区：
文献类型：
--
作者：
V. Tsai;C. Huber;C. Dalton
地震层析成像是地球物理学的基石，带来了许多关于地球内部的重要发现。然而，在大多数层析成像应用中，地震层析成像仍然受到大量未知参数的困扰。这导致逆问题不确定，并且需要大量的非地质驱动的平滑才能获得唯一的答案。尽管当在发现模式中使用层析成像作为勘探工具时，该解决方案是可以接受的，但它在使用层析成像来区分可接受的地质模型或估计地质相关参数时提出了一个重大问题，因为即使考虑到不确定性，通常所考虑的地质模型都不适合层析成像结果。为了应对这一挑战，当地震层析成像用于地质模型选择或参数估计目的时，我们主张可以根据正在测试的地质模型对层析成像进行明确参数化，而不是使用更数学上方便的公式，如体素、样条曲线或球谐函数。我们的提议有许多与之相关的技术困难，其中一些最重要的困难是从线性反演问题转向非线性反演问题，需要选择适合每个特定问题并与预期数据质量和结构相称的地质参数化，以及需要使用支持框架来确定断层扫描数据首选哪种模型。在这篇文章中，我们介绍了层析成像的地质参数化，其中包括一些应用于沉积盆地和俯冲带成像的简单综合示例，以及推断美国大陆盆地和地壳特性的一个真实示例。我们解释了走向更现实的例子所面临的挑战，并讨论了主要的技术困难以及如何克服它们。虽然本文建议的科学计划可能需要数年时间才能达到成熟，但如果地震层析成像要从一种发现合理结构的工具发展为可以对结构的存在或不存在及其物理特征做出明确的科学推论的工具，则有必要朝这个方向采取步骤。
Seismic tomography is a cornerstone of geophysics and has led to a number of important discoveries about the interior of the Earth. However, seismic tomography remains plagued by the large number of unknown parameters in most tomographic applications. This leads to the inverse problem being underdetermined and requiring significant non-geologically motivated smoothing in order to achieve unique answers. Although this solution is acceptable when using tomography as an explorative tool in discovery mode, it presents a significant problem to use of tomography in distinguishing between acceptable geological models or in estimating geologically relevant parameters since typically none of the geological models considered are fit by the tomographic results, even when uncertainties are accounted for. To address this challenge, when seismic tomography is to be used for geological model selection or parameter estimation purposes, we advocate that the tomography can be explicitly parametrized in terms of the geological models being tested instead of using more mathematically convenient formulations like voxels, splines or spherical harmonics. Our proposition has a number of technical difficulties associated with it, with some of the most important ones being the move from a linear to a non-linear inverse problem, the need to choose a geological parametrization that fits each specific problem and is commensurate with the expected data quality and structure, and the need to use a supporting framework to identify which model is preferred by the tomographic data. In this contribution, we introduce geological parametrization of tomography with a few simple synthetic examples applied to imaging sedimentary basins and subduction zones, and one real-world example of inferring basin and crustal properties across the continental United States. We explain the challenges in moving towards more realistic examples, and discuss the main technical difficulties and how they may be overcome. Although it may take a number of years for the scientific program suggested here to reach maturity, it is necessary to take steps in this direction if seismic tomography is to develop from a tool for discovering plausible structures to one in which distinct scientific inferences can be made regarding the presence or absence of structures and their physical characteristics.