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

本项目的重点是1)开发一种新的层析成像方法，该方法集成了地震表面波和散射体波相位的互补分辨能力；2)将该方法应用于EarthScope USArray永久骨干网组件的数据，并辅以可传输阵列的数据。这项工作将对北美上地幔的三维各向异性地震速度结构产生更高的分辨率约束，特别关注大陆岩石圈和软流圈的局部厚度和结构非均质性。更高分辨率的模型将解决有关大陆岩石圈的演化及其与更深地幔的动态关系的问题。大陆岩石圈的性质如何随年龄变化？岩石圈-软流圈边界（LAB）的本质是什么？在不同构造历史的地区，它是如何变化的？地震速度各向异性如何在整个拉布拉多地区变化？它与当今的流动和/或过去的构造事件有何关系？在伯克利，我们已经开发了反演长周期地震图的方法，以构建包括径向和方位各向异性的区域上地幔速度模型，并可以纳入其他约束条件，如远震剪切波分裂数据，我们已经将这种方法应用于北美。然而，最终的模型在横向和纵向上都是平滑的，并且不包含像LAB这样的尖锐边界。在布朗，我们开发了利用远震S到P （Sp）和P到S （Ps）散射波成像地幔中地幔急剧速度界面的方法，在北美东部，我们在深度约90公里处发现了一个向西倾斜的不连续面，我们将其确定为LAB。然而，这种方法只提供了车站附近的限制条件，而不能提供有关不连续点上下的体积结构的信息。最初的重点是方法开发——结合这两种方法——以及用来自永久骨干网的数据测试该方法；来自可移动阵列的数据将在稍后的项目中纳入。这项工作将弥合目前平滑、大规模层析成像建模与更高分辨率建模之间的差距，更高分辨率建模将可能与更密集间隔的EarthScope柔性阵列实验站一起实现。

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.