Understanding and Performing High-Resolution Surface-Wave Attenuation Measurements with USArray

“利用USArray理解和执行高分辨率表面波衰减测量”这个项目的重点是利用地震波振幅来获得地壳和上地幔的高分辨率图像。利用表面波的传播时间进行速度成像已经非常成功，但对这些速度图像的解释并不独特。这里进行的振幅分析不仅约束了速度结构，而且约束了密度和衰减结构。这些额外的知识有助于解决非唯一性问题，从而更好地约束北美大陆的变形历史、演化、地球化学和构造结构的关键特征。特别是，高分辨率衰减测量对岩浆和部分熔体、水和其他挥发物以及断层结构等特征具有潜在的敏感性，因为与地震速度相比，这些特征对固有衰减的依赖性不同。与以前的衰减和密度成像相比，这项工作提供了更高分辨率的图像，这是由于USArray与新的数据处理技术相结合，大大提高了台站覆盖范围。一方面，理论和经验技术的发展允许使用环境噪声衰减层析成像，即使噪声源分布不均匀。与基于地震的研究相比，这些环境噪声方法有望提高空间分辨率，部分原因是增加了测量成功的频带。另一方面，基于阵列的相前跟踪和幅度测绘的发展使得利用USArray的密集站点覆盖来考虑聚焦和散焦效应并减少源不确定性的影响成为可能。这一理论、数值和经验工作的结合，使得对环境噪声和地震的表面波振幅的精确测量成为可能，并使得这里所考虑的密度和衰减成像成为可能。

"Understanding and Performing High-Resolution Surface-Wave Attenuation Measurements with USArray"This project focuses on making use of seismic wave amplitudes to achieve high-resolution images of the Earth's crust and upper mantle. Velocity imaging using the travel times of surface waves has been extremely successful, but interpretations of these velocity images are non-unique. The amplitude analysis performed here constrains not only velocity structure, but also density and attenuation structure. This extra knowledge helps solve the non-uniqueness problem, allowing better constraints on key features of the North American continent's deformation history, evolution, and geochemical and tectonic structure. In particular, the high-resolution attenuation measurements are potentially sensitive to features such as magma and partial melt, water and other volatiles, as well as fault structures through the differing dependencies of these features on intrinsic attenuation as compared with seismic velocities.This work provides higher resolution images compared to previous attenuation and density imaging due to the confluence of vastly improved station coverage by USArray with new data processing techniques. On one hand, developments in theoretical and empirical techniques allow for utilization of ambient noise attenuation tomography, even when the noise sources are non-uniformly distributed. These ambient noise methods promise to allow for improved spatial resolution compared to earthquake-based studies due partly to the increased frequency band over which measurements are successful. On the other hand, developments in array-based phase-front tracking and amplitude mapping make it possible to use the dense station coverage of USArray to account for focusing and defocusing effects and to reduce the influence of source uncertainty. The convergence of this theoretical, numerical and empirical work allows for accurate measurements of surface-wave amplitudes, both for ambient noise and earthquakes, and allows for the density and attenuation imaging considered here.