Collaborative Research: Characterizing North American Upper Mantle Structure with Integrated Inversions of USArray Surface Wave and Scattered Body Wave Data

该项目的重点是：1）开发一种新的层析成像方法，该方法集成了地震面波和散射体波相位的互补分辨率; 2）将该方法应用于EarthScope USAray的永久骨干网络组件的数据，并由可移动阵列的数据补充。这项工作将导致北美上地幔的三维各向异性地震速度结构的更高分辨率的限制，特别侧重于大陆岩石圈和软流圈的局部厚度和结构的不均匀性。更高分辨率的模式将解决有关大陆岩石圈演化及其与更深地幔的动力学关系的问题。大陆岩石圈的性质如何随年龄而变化？岩石圈-软流圈边界（LAB）的性质是什么？它在不同构造历史的地区是如何变化的？地震速度各向异性在整个LAB中是如何变化的？它与现今的流动和/或过去的构造事件有何关系？ 在伯克利，我们已经开发出了反演长周期地震图的方法，以构建区域上地幔速度模型，该模型包括径向和方位各向异性，并可以包含其他约束，如径向剪切波分裂数据，我们已经将这种方法应用于北美。然而，所得到的模型在横向和纵向上是平滑的，并且不包含诸如LAB的尖锐边界。在布朗，我们已经开发出的方法，采用Escherichia S到P（Sp）和P到S（Ps）散射波成像地幔中的地幔尖锐的速度界面，在北美东部，我们已经检测到存在一个向西倾斜的不连续性在深度约90公里，我们确定为LAB。然而，该方法仅在测站附近提供了约束条件，而不提供有关不连续面上方和下方的体积结构的信息。最初的重点是方法开发-将两种方法结合起来-以及使用永久主干网的数据测试该方法;来自可移动阵列的数据将在稍后纳入项目。这项工作将弥合目前的平滑，大规模层析成像建模和更高的分辨率建模之间的差距，这将是可能与更密集的间隔站的EarthScope灵活阵列实验。

This project focuses on 1) the development of a new tomographic method that integrates the complementary resolving power of seismic surface waves and scattered body wave phases and 2) the application of this method to data from the permanent Backbone Network component of the EarthScope USArray, complemented by data from the Transportable Array. This work will result in higher resolution constraints on the three-dimensional anisotropic seismic velocity structure of the North American upper mantle, with a particular focus on the local thickness and structural heterogeneity of the continental lithosphere and asthenosphere. Higher resolution models will address questions regarding the evolution of the continental lithosphere and its dynamic relationship to the deeper mantle. How do the properties of the continental lithosphere vary as a function of age? What is the nature of the lithosphere-asthenosphere boundary (LAB) and how does it vary across regions with different tectonic histories? How does seismic velocity anisotropy vary across the LAB and how does it relate to present day flow and/or past tectonic events? At Berkeley, we have developed methods for inverting long period seismograms to construct regional upper mantle velocity models that include both radial and azimuthal anisotropy and can incorporate other constraints, such as teleseismic shear-wave splitting data, and we have applied this approach to North America. However, the resulting models are laterally and vertically smooth and do not incorporate sharp boundaries such as the LAB. At Brown, we have developed methods that employ teleseismic S to P (Sp) and P to S (Ps) scattered waves to image mantle sharp velocity interfaces in the mantle, and in eastern North America we have detected the presence of a westward dipping discontinuity at depths of ~90 km that we identify as the LAB. However, this approach provides constraints only in the vicinity of stations, and does not provide information about the volumetric structure above and below the discontinuity.The initial focus is on method development - combining the two approaches - and on testing the approach with data from the permanent Backbone Network; data from the Transportable Array will be incorporated later in the project. This work will bridge the gap between current smooth, large-scale tomographic modeling and the higher resolution modeling which will be possible with the more densely spaced stations of EarthScope Flexible Array experiments.