Analysis of Seismic Data from the USArray Project to Determine Crust and Uppermost Mantle Structure Beneath the United States

在过去的十年中，NSF的USAray项目在美国各地部署了数千个地震仪来记录本地和远程地震。 对这些数据的分析提供了美国地壳和地幔结构的改进图像。 该项目研究USAray在1600公里（1000英里）外记录的地震和采石场爆炸，这对探测地壳厚度和最上层地幔的结构特别有用，即，在地壳之下，大约35到50公里（大约20到30英里）的深度。 显示该地区测得的地震波速度变化的地图提供了有关山脉、断层和其他地质特征（包括科罗拉多高原和黄石火山活动）的历史和演变的线索。 该项目以美国国家科学基金会以前资助的美国西部工作为基础，重点关注美国东部最近的USAray数据，特别是，该项目使用区域地震震相，如Pn、Sn、Pg和Lg，绘制新的地壳厚度图以及与许多地表构造特征有关的上地幔P和S速度的各向同性和各向异性变化图。这些结果一般同意与以前的研究在其大规模的模式，但在许多地区显示更多的细节。由于其相对稀疏的站点覆盖和缺乏地震，美国东部的研究比西部少得多，因此最近的USAray站点部署提供了一个宝贵的机会，以探测其地壳和上地幔结构。该项目将提供新的地壳厚度图、地壳Vp/Vs比估计值、地震速度和方位各向异性的上地幔变化图。此外，计划分析Sn传播效率和Pg和Lg时间和振幅，以解决较低的地壳速度和衰减。 这些结果将补充剪切波分裂和表面波和体波层析成像研究提供上级分辨率的结构在地壳下部和地幔上部的深度。

During the last ten years, NSF's USArray Project has deployed thousands of seismometers across the United States to record both local and distant earthquakes. Analyses of these data have provided greatly improved images of the structure of Earth's crust and mantle beneath the United States. This project studies earthquakes and quarry blasts recorded by USArray at distances up to 1600 km away (1000 miles), which are particularly useful for probing crustal thickness and the structure of the uppermost mantle, i.e., immediately below the crust at depths of about 35 to 50 kilometers (about 20 to 30 miles). Maps showing variations in the measured velocities of seismic waves in this region provide clues regarding the history and evolution of mountains, faults, and other geological features, including the Colorado Plateau and Yellowstone volcanism. This project builds on previously NSF funded work in the western United States to focus on more recent USArray data from the eastern United States.In particular, the project uses regional seismic phases such as Pn, Sn, Pg and Lg, to produce new maps of crustal thickness and both isotropic and anisotropic variations in uppermost mantle P and S velocity that can be related to many surface tectonic features. These results generally agree with previous studies in their large-scale patterns but show more detail in many regions. Owing to its relatively sparse station coverage and lack of earthquakes, the eastern United States has been much less studied than the west, so the most recent USArray station deployments provide a valuable opportunity to probe its crust and uppermost mantle structure. This project will provide new crustal thickness maps, estimates of crustal Vp/Vs ratios, maps of uppermost mantle variations in seismic velocity and azimuthal anisotropy. In addition, analyses of Sn propagation efficiency and Pg and Lg times and amplitudes are planned to resolve lower crustal velocities and attenuation. These results will complement shear-wave splitting and surface- and body-wave tomography studies by providing superior resolution for structures at lower crustal and uppermost mantle depths.