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

Ritzwoller提出的研究将推进和应用一种新的面波层析成像方法，该方法基于与地震发生无关的面波频散测量。该方法基于通过相互关联形成随机地震波场一部分的环境或背景地震噪声序列来提取面波格林函数。对美国境内不同距离的台站进行的概念验证实验表明，用这种方法进行的色散测量是可重复的，并重现了地震后弹道波的传统测量提供的信息。基于噪声的面波测量使我们能够构建加利福尼亚州下面主要地质单元的层析图像，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芯。这种方法可以提高从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的背景下，如EarthScope的美国阵列组件，其中许多台间面波测量有望聚焦美国下方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。第一是提高对背景地震噪声的认识，并继续发展一种稳健的方法，从两个台站互相关来测量面波频散。第二个目标是将该方法应用于模拟和新兴的US数组数据。分析将集中在三个空间尺度上：(1)大陆尺度，利用美国国家地震台网(USNSN)和全球地震台网(GSN)的数据，以及新兴的高级国家地震系统(ANSS)的宽带组成部分，类似于USAR阵的永久组成部分；(2)区域尺度，类似于USAR阵的可运输组成部分，使用加利福尼亚州和落基山脉的宽带阵列数据；(3)局部尺度，类似于部署USAR阵的灵活组成部分和PASSCAL实验，使用南加州和黄石地区的阵列数据。

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.