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

该项目的重点是利用EarthScope/USAray便携式阵列上记录的数据，采用各种分析方法，调查基模表面波在北美的传播情况。该研究的一个目标是开发北美地区全面的高分辨率相速度地图，以帮助限制大陆的深层结构。 短周期和中周期面波的传播取决于地壳和浅地幔的弹性结构，因此，对这些波的传播特性的观测有助于约束地球内部这一部分的状态、组成和动力学。EarthScope/USAray的可移动阵列正在利用表面波生成一个前所未有的数据集，用于北美地壳和地幔的地震成像，该项目旨在利用三种方法利用这些数据。首先，该项目涉及收集一套新的观测地震记录在USAray站的表面波偏振。由于USAArray站的统一校准，以及用于确定USAArray站方向的最新技术，该数据集非常适合极化研究。其次，最近开发的方法，分析交叉频谱的环境噪声记录在两个地震台站间的面波频散的测定系统地适用于USAray站。该方法，这是基于阿基的开创性的1957年的论文，允许爱和瑞利波相速度被自动映射到整个足迹的USAray在空间分辨率小于100公里，并在短至5秒的周期。第三，从短期环境噪声和中期地震信号得出的相速度图被用来确定北美大陆地壳和最上地幔的弹性结构，该项目将导致改进整个北美的表面波传播特性，并将促进对地球内部的组成和热状态作出更具体的解释。几个记录的数据集，可以为其他研究人员希望限制北美下面的弹性结构有用将从研究中产生。

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.