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

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非均质性，波速波动Vp高达+/-6%，VS高达+/-8-9%。这些异常通常是在用射线理论方法用远震数据发现的大小处于分辨率边缘的天体中发现的。最近在层析成像反演中结合了波形特征(即脂肪射线或香蕉甜甜圈)的工作已经照亮了以前难以成像的较小规模的异常，例如来自地幔更深部分的低速带的异常。地幔中较大的尺度波动既表明了化学变化，也表明了物理状态的差异(如熔融阶段)以及温度波动。确定地震速度分布的几何形状和幅度是了解地球表面和上地幔地球动力学的重要手段。尽管旅行时间层析成像在地球内部成像方面取得了巨大的成功，但层析图像的相对粗糙导致了一种情况，即大小尺度对流引起的地幔环流和地幔非均质性的细节仍然不清楚。本研究项目的目标是开发和应用远震数据的迭代弹性波层析成像技术。这是一种通过迭代数据拟合形成地震成像的方法，即地震反问题的优化公式，它需要一种模拟地震波传播的方法，以及一种更新(AN)弹性波动方程中的部分或全部参数的方法，以使模拟的波场与一组观测数据相匹配或拟合。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来自地球望远镜的美国阵列组件的数据，并允许更好地解释北美以下地壳和上地幔的结构。这在美国西部尤其重要，那里的地震和火山都是科学上知之甚少的自然灾害。波形层析成像的发展，特别是结合速度分析的扩展变种的发展，也会对未来十年用于石油储量勘探的工业地震技术的发展产生重大影响。我们工作中解决的许多问题在工业背景下也是紧迫的；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。我们很大一部分学生毕业后就进入了石油行业，所以这个项目应该会提供一个极好的和不同寻常的前瞻性培训资源。在这个项目中进行的研究的理论和实践方面将向科学界传播，特别是研究生和博士后研究人员，部分方式是通过一系列关于成像科学的研讨会，该研讨会由NSF地球望远镜计划在未来3年内资助，并由该赠款的一个私人投资者组织。

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.