CMG: Adjoint, Migration, and Velocity Analysis Methods for Imaging the Earth's Upper Mantle: Theory and Application

CMG：地球上地幔成像的伴随、迁移和速度分析方法：理论与应用

• 批准号: 0620821
• 负责人: Alan Levander
• 金额: $ 50万
• 依托单位: William Marsh Rice University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-09-01 至 2012-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0620821&HistoricalAwards=false
• 关键词: CMG; Adjoint; Migration; Velocity; Analysis

Regional and global seismic travel time tomography studies show that the Earth's upper mantle has a high degree of lateral heterogeneity, with fluctuations in seismic velocities up to +/- 6% in Vp and +/- 8-9% in Vs. These anomalies are often found in bodies whose size is at the edge of resolution with teleseismic data using ray-theoretical methods. Recent work to incorporate aspects of wave character (i.e., fat rays or banana-donuts) in the tomographic inversions has illuminated smaller scale, previously hard to image anomalies, such as those from low velocity zones in the deeper parts of the mantle. The larger scale fluctuations in the mantle are indicative of both chemical variations and physical state differences (e.g. melt phases) as well as temperature fluctuations. Determining the geometry and amplitude of the seismic velocity distribution is an important means of understanding the geodynamics of the Earth's surface and and upper mantle. Despite the great successes in imaging the Earth's interior using travel time tomography, the relative coarseness of tomography images has led to a situation in which details of mantle circulation and mantle hetereogeneity derived from large and small scale convection are still obscure. The goal of this research project is develop and apply iterative elastic waveform tomography to teleseismic data. This is a means of seismic image formation by iterative data fitting, i.e., an optimization formulation of the seismic inverse problem which requires a method for simulating the propagation of seismic waves, and a method to update some or all parameters in the (an)elastic wave equation so that the simulated wavefield matches or fits a collection of observed data. Waveform tomography has the possibility of improving the resolution of images of the Earth's upper mantle by more than an order of magnitude.High resolution images made with waveform tomography will more thoroughly utilize the data from the USArray component of Earthscope and permit better geological interpretations of the structure of the Earth's crust and upper mantle beneath North America. This is particularly important in the western U.S., where both earthquakes and volcanoes are scientifically poorly understood natural hazards. The development of waveform tomography generally, and of extended variants incorporating velocity analysis in particular, also can significantly affect the development of industrial seismic technology used in the exploration for petroleum reserves over the coming decade. Many of the issues addressed in our work are also pressing in the industrial context; advances in algorithm design and computer performance offer similar opportunities for improved imaging. A significant fraction of our students enter the oil industry upon graduation, so this project should provide an excellent and unusually forward-looking training resource. The theoretical and practical aspects of the research undertaken in this project will be disseminated to the scientific community, particularly graduate students and post-doctoral researchers, in part through a series of workshops on imaging science that has been funded by the NSF Earthscope program in the coming 3 years, and being organized by one of the PIs of this grant.

区域和全球地震走时层析成像研究表明，地球上地幔具有高度的横向不均匀性，Vp的地震速度波动高达+/- 6%，Vs的地震速度波动高达+/- 8-9%。最近的工作，以纳入方面的波的特点（即，脂肪射线或香蕉甜甜圈）的层析成像反演照亮了较小的规模，以前很难成像异常，如那些来自低速区在地幔的较深的部分。 地幔中较大尺度的波动表明了化学变化和物理状态差异（例如熔融相）以及温度波动。确定地震速度分布的几何形状和振幅是了解地球表面和上地幔地球动力学的重要手段。尽管利用走时层析成像在地球内部成像方面取得了巨大的成功，但层析成像图像的相对粗糙导致了一种情况，即地幔环流和地幔不均匀性的细节来自大小尺度对流仍然是模糊的。本研究计画的目的是发展并应用弹性波迭波层析成像技术于地震资料。 这是一种通过迭代数据拟合形成地震图像的方法，即，地震逆问题的优化公式，需要一种模拟地震波传播的方法，以及一种更新弹性波方程中的部分或所有参数的方法，以便模拟的波场匹配或拟合观测数据的集合。波形层析成像有可能将地球上地幔图像的分辨率提高一个数量级以上，用波形层析成像制作的高分辨率图像将更充分地利用Earthscope的USAray组件的数据，并能对北美地壳和上地幔的结构作出更好的地质解释。这在美国西部尤为重要，地震和火山都是科学上知之甚少的自然灾害。 波形层析成像技术的发展，特别是结合速度分析的扩展变体的发展，也会在未来十年内对石油储量勘探中使用的工业地震技术的发展产生重大影响。在我们的工作中解决的许多问题在工业环境中也是紧迫的;算法设计和计算机性能的进步为改进成像提供了类似的机会。我们的学生毕业后进入石油行业的一个显着的一部分，所以这个项目应该提供一个优秀的和异常前瞻性的培训资源。在这个项目中进行的研究的理论和实践方面将传播给科学界，特别是研究生和博士后研究人员，部分通过一系列成像科学研讨会，该研讨会由NSF Earthscope计划在未来3年内资助，并由该补助金的PI之一组织。