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的互补分辨率，以及2)将该方法应用于来自EarthScope USArray永久主干网络组件的数据，并辅之以来自可移动阵列的数据。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分辨率的约束，特别是对大陆岩石圈和软流圈的局部厚度和结构不均一性的限制。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力学关系的问题。大陆岩石圈的性质如何随年龄的变化而变化？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之间是如何变化的？地震速度各向异性在整个实验室中是如何变化的，它与今天的流动和/或过去的构造事件有什么关系？在伯克利，我们开发了反演长周期地震记录的方法，以建立既包括径向各向异性又包括方位各向异性的区域上地幔速度模型，并可以包括其他约束条件，如远震剪切波分裂数据，我们已将这种方法应用于北美。但是，生成的模型在横向和垂直方向上都是平滑的，并且不包含像LAB这样的清晰边界。在布朗，我们发展了利用远震S到P(Sp)和P到S(Ps)散射波来成像地幔中的急剧速度界面的方法，在北美东部，我们探测到在大约90公里深处存在一个向西倾斜的不连续面，我们将其识别为实验室。然而，这种方法只在站点附近提供限制，不提供关于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--结合两种方法--以及使用来自永久骨干网络的数据来测试该方法；来自可移动阵列的数据将在稍后的项目中纳入。这项工作将弥合当前平滑的大规模层析成像建模与更高分辨率的建模之间的差距，而更高分辨率的建模将可能通过更密集的EarthScope柔性阵列实验的站点来实现。

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.