Surface-wave Propagation Across North America: New Methods, Observations and Models

该项目的重点是利用EarthScope/USArray可移动阵列记录的数据，采用多种分析方法，研究基模表面波在北美的传播。这项研究的一个目标是开发横跨北美的全面高分辨率相速度地图，以帮助限制该大陆的深层结构。短周期和中期表面波的传播取决于地壳和浅地幔的弹性结构，因此对这些波的传播特征的观测对于限制地球内部这部分的状态、组成和动力学是有用的。EarthScope/USArray的可移动阵列正在生成一个前所未有的数据集，用于利用表面波对北美地壳和地幔进行地震成像，该项目旨在利用三种方法来利用这些数据。首先，该项目涉及收集USArray台站记录的一组新的地震表面波极化观测数据。由于USArray站的统一校准，以及使用最先进的技术来定位USArray站，该数据集非常适合偏振研究。其次，最近开发的一种分析两个地震台站记录的环境噪声交叉谱的方法用于确定台站间表面波色散，并系统地应用于USArray台站。该方法基于Aki 1957年开创性的论文，允许在USArray覆盖范围内以小于100公里的空间分辨率自动绘制Love波和Rayleigh波相速度，周期短至5秒。第三，结合短周期环境噪声和中期地震信号的相速度图，确定了北美大陆地壳和上地幔的弹性结构。该项目将改进整个北美的表面波传播特性，并将促进对地球内部成分和热状态的更具体解释。一些记录的数据集可以对其他希望约束北美地下弹性结构的研究人员有用。

The project is focused on investigating the propagation of fundamental-mode surface waves across North America using data recorded on the EarthScope/USArray Transportable Array employing a variety of methods of analysis. A goal of the research is the development of comprehensive high-resolution maps of phase velocity across North America to help constrain the deep structure of the continent. The propagation of short- and intermediate-period surface waves depends on the elastic structure of the crust and shallow mantle, and observations of propagation characteristics of these waves are therefore useful for constraining the state, composition and dynamics of this portion of the Earth's interior. The Transportable Array of EarthScope/USArray is generating an unprecedented data set for the seismological imaging of the North American crust and mantle using surface waves, and the project aims to exploit these data using three approaches. First, the project involves the collection of a new set of observations of surface-wave polarization for earthquakes recorded on USArray stations. Owing to the uniform calibration of USAarray station, and the state-of-the-art technology used to orient USArray stations, this data set is ideally suited for polarization studies. Second, a recently developed method of analyzing cross spectra of ambient noise recorded on two seismic stations for the determination of inter-station surface-wave dispersion is applied systematically to USArray stations. The method, which is based on Aki's seminal 1957 paper, allows Love and Rayleigh wave phase velocities to be mapped automatically across the footprint of USArray at a spatial resolution smaller than 100 km, and at periods as short as 5 s. Third, the phase velocity maps derived from short-period ambient noise and intermediate-period earthquake signals are used, together, to determine the elastic structure of the crust and uppermost mantle of the North American Continent.The project will lead to an improved characterization of surface-wave propagation across North America and will facilitate more specific interpretation of the composition and thermal state of the Earth's interior. Several documented data sets that can be useful for other investigators wishing to constrain the elastic structure beneath North America will result from the research.