Seismic Observations from the Random Wavefield: A New Tool for High-Resolution Seismology in the Context of EarthScope

本文提出的研究将推进并应用一种新的基于不依赖于地震发生的表面波频散测量的表面波层析成像方法。该方法是通过构成随机地震波场一部分的环境或背景地震噪声的相互关联序列提取表面波格林函数。在美国境内相隔不同距离的台站进行的概念验证实验表明，用这种方法进行的频散测量是可重复的，并再现了地震后弹道波的传统测量所提供的信息。基于噪声的表面波测量使我们能够构建加利福尼亚地下主要地质单元的层析成像，其中低速异常对应于主要沉积盆地，高速异常对应于主要山脉的火成岩岩心。这种方法可以提高从表面波分析中获得的地壳图像的分辨率和保真度，特别是在大陆尺度阵列（如EarthScope的USARRAY组件）的背景下，许多站间表面波测量有望聚焦美国地壳和上地幔的地震图像和模型。拟议的工作有两个主要目标。首先是提高对背景地震噪声的理解，并继续开发一种可靠的方法来测量两站互相关的表面波频散。第二个目标是将该方法应用于模拟和新兴的USARRAY数据。分析将集中在三个空间尺度上：(1)大陆尺度，类似于USARRAY的永久分量，使用来自美国国家地震台网（USNSN）和全球地震台网（GSN）的数据，以及新兴的先进国家地震系统（ANSS）的宽带分量；(2)区域尺度，类似于USARRAY的可移动组件，使用来自加利福尼亚和落基山脉宽带阵列的数据；(3)局部规模，类似于USARRAY和pascal实验中灵活组件的部署，使用来自南加州和黄石地区阵列的数据。

0450082RitzwollerThe proposed research will advance and apply a new method of surface-wave tomography based on measurements of surface wave dispersion that are independent of earthquake occurrence. The method is based on the extraction of surface-wave Green functions by cross-correlating sequences of ambient or background seismic noise that form part of the random seismic wavefield. Proof-of-concept experiments for stations separated by various distances within the US demonstrate that dispersion measurements made with this method are repeatable and reproduce information provided by traditional measurements obtained on ballistic waves following earthquakes. Noise-based surface- wave measurements allow us to construct tomographic images of the principal geological units beneath California, with low-speed anomalies corresponding to the main sedimentary basins and high-speed anomalies corresponding to the igneous cores of the major mountain ranges. This method can improve the resolution and fidelity of crustal images obtained from surface-wave analyses, in particular, in the context of a continental scale array such as the USARRAY component of EarthScope, where numerous inter-station surface-wave measurements promise to focus seismic images and models of the crust and upper mantle beneath the US. The proposed work has two principal objectives. The first is to improve understanding of background seismic noise and to continue to develop a robust method to measure surface-wave dispersion from two-station cross-correlation. The second objective is to apply the method to analog and emerging USARRAY data. Analysis will concentrate on three spatial scales: (1) continental-scale, analogous to the permanent component of USARRAY, using data from the US National Seismic Network (USNSN) and the Global Seismic Network (GSN), as well as the broad-band component of the emerging Advanced National Seismic System (ANSS); (2) regional-scale, analogous to the transportable component of USARRAY, using data from broad-band arrays in California and the Rocky Mountains; and (3) local-scale, analogous to deployments of the flexible component of USARRAY and PASSCAL experiments, using data from arrays in Southern California and the Yellowstone areas.