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，在Vp和vs中，地震速度的波动可达+/- 6%和+/- 8-9%。这些异常通常出现在使用射线理论方法获得的远震数据分辨率边缘的体中。最近的工作将波浪特征（即脂肪射线或香蕉甜甜圈）纳入断层成像反演，揭示了以前难以成像的小尺度异常，例如来自地幔深层低速带的异常。地幔的较大尺度波动表明化学变化和物理状态差异（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振幅是了解地表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，但层析成像图像的相对粗糙导致了大尺度和小尺度对流衍生的地幔环流和地幔非均质性细节仍然模糊不清。本课题的研究目标是开发并应用迭代弹性波形层析成像技术处理远震数据。这是一种通过迭代数据拟合来形成地震图像的方法，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，使模拟波场与观测数据集合相匹配或拟合。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。波形层析成像的高分辨率图像将更充分地利用地球望远镜USArray组件的数据，并允许对北美地壳和上地幔结构进行更好的地质解释。这在美国西部尤为重要，在那里，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体的发展，也会显著影响未来十年石油储量勘探中使用的工业地震技术的发展。我们工作中涉及的许多问题在工业背景下也很紧迫；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。我们的学生中有很大一部分在毕业后进入石油行业，所以这个项目应该提供一个优秀的和不同寻常的前瞻性培训资源。本项目研究的理论和实践方面将向科学界，特别是研究生和博士后研究人员传播，部分是通过由NSF Earthscope计划在未来3年内资助的一系列成像科学研讨会，并由该基金的一个pi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.