Ambient Noise and Teleseismic Tomography to infer the Physical State and Structure of the Crust and Upper Mantle in the Western United States

我们寻求推进和应用两种强大的新的互补表面波层析成像方法，以快速积累美国西部的数据资源，主要来自EarthScope/USArray的可移动阵列（TA）组件。两种方法分别是环境噪声层析成像和两平面波远震层析成像。环境噪声层析成像（ANT）是基于通过相互关联构成随机地震波场一部分的环境或背景地震噪声长序列来提取表面波格林函数。双平面波层析成像（TPWT）根据阵列足迹内的相速度变化解释了在区域地震阵列上观测到的远震表面波的振幅和相位变化，重要的是，它还模拟了由地震和阵列之间发生的散射引起的入射波场的波纹。两种方法都测量表面波色散，但在互补的周期波段：ANT（6 - 40秒）和TPWT（25 - 150秒）。结合使用，这些方法能够在25-50公里的地理网格上，从6秒到150秒的时间内产生整个TA的色散曲线（瑞利波和洛夫波，群速度和相速度）。就在三年前，表面波地震学家还无法预见到这种前景。在这些方法的分辨率下（横跨TA的70公里），这些色散曲线中包含的信息内容在如此大的区域内是前所未有的。提出的研究将使用蒙特卡罗方法根据地壳和上地幔200公里深处的剪切速度变化来解释频散图，该方法可以返回三维模型和不确定性。这里提出的研究将对了解美国西部地壳和上地幔的物理状态和结构产生深远的影响。我们预计这将对区域尺度构造的研究以及美国西部地下岩石圈的热量和成分状态产生重大影响，进而对世界其他地方类似的大陆区域产生重大影响。所提出的数据处理和综合反演方法将为参与的学生和博士后提供独特的教育体验。此外，应用于USArray数据的方法在其他区域阵列安装时也适用；例如，在欧洲和中国，也用于PASSCAL安装。研究团队在为广泛的社区提供数据产品、模型和软件方面有着强大的跟踪记录，并且该研究产生的数据集、分散图和模型将普遍可用。由此产生的模型也将与地震危害评估相关，既可以用于地面运动模拟，也可以用于改进和扩展社区模型，如SCEC 3D参考模型。最后，新的高分辨率反演方法的应用将有助于实现USArray？以前所未有的细节模拟了美国地下的地球研究小组制作的跟踪可移动阵列部署时色散图出现情况的影片定期在EarthScope审查会议上放映。拟议的研究结果也将被视为实现美国地震学界对EarthScope的愿景的重要组成部分。

We seek to advance and apply two powerful new complementary methods of surface wave tomography to rapidly accruing data resources in the western US, predominantly from the Transportable Array (TA) component of EarthScope/USArray. The two methods are ambient noise tomography and two-plane wave teleseismic tomography. Ambient noise tomography (ANT) is based on the extraction of surface-wave Green functions by cross-correlating long sequences of ambient or background seismic noise that form part of the random seismic wavefield. Two plane-wave tomography (TPWT) interprets the variation in amplitude and phase of teleseismic surface waves observed across a regional seismic array in terms of phase velocity variations within the foot-print of the array and, importantly, also models corrugations in the incoming wavefield caused by scattering that occurs between the earthquake and array.Both methods measure surface wave dispersion, but in complementary period bands: ANT (6 - 40 sec) and TPWT (25 - 150 sec). Used in combination, the methods are able to produce dispersion curves (Rayleigh and Love wave, group and phase velocity) across the entire TA from about 6 sec to 150 sec period on a 25-50 km geographic grid. This prospect could not have been foreseen by surface wave seismologists as little as 3 years ago. The information content contained in these dispersion curves at the resolution of these methods ($\sim$70 km across the TA) over a region as large as that proposed is unprecedented. The proposed research will interpret the dispersion maps in terms of shear velocity variations within the crust and upper mantle to a depth of 200 km using a Monte-Carlo method, which returns both the 3-D model and uncertainties. The research proposed here will have a profound impact on the understanding of the physical state and structure of the crust and upper mantle beneath the western US.We anticipate significant impacts on studies of regional-scale tectonics as well as the thermal and compositional state of the lithosphere beneath the western US and, by extension, similar continental regions elsewhere in the world. The proposed data processing and integrative inversion methodology will offer a unique educational experience for the students and post-doctoral staff involved. Moreover, the methods applied to the USArray data are applicable elsewhere as other regional arrays are installed; e.g., in Europe and China and also for PASSCAL installations. The research team has a strong track record of making data products, models, and software available to a wide community, and the data sets, dispersion maps, and models that result from this research will be made generally available. The resulting model also will have relevance for seismic hazard assessment, both for ground motion simulation and to improve and extend community models such as the SCEC 3D reference model. Finally, the application of the new high-resolution inversion methods will help to achieve the vision of the USArray?modeling the Earth beneath the US in unprecedented detail. Movies produced by the research team that track the emergence of dispersion maps as the Transportable Array has been deployed are shown regularly at EarthScope review meetings. The results of the proposed research will also be seen as important components in achieving the US seismological community''s vision for EarthScope.