Autocorrelation of Seismic Ambient Noise and P-wave Coda for Crustal Structure

该项目开发新方法，探索如何利用地震测量中的噪声更好地对地球地壳结构进行成像。这些新方法很重要，因为世界上许多地区都是地震区，而且受控的人造地震源很昂贵。因此，使用现有的非地震信号（称为环境噪声）来成像地球的新方法可以在许多地方使用，例如中西部。将在几个月的时间内以Earthscope地震台站SFIN为中心部署12个便携式地震台站。然后，这些方法将被应用到选定的地震台站在中部中西部的上部与类似的环境噪声特性，以测试的一致性的方法和图像的地壳伸展从爱荷华州到俄亥俄州。他们将通过最近在俄克拉荷马州进行的“大N”IRIS社区波场演示实验来比较这项工作。由于俄克拉荷马州阵列的孔径与SFIN的小规模阵列相当，因此将比较两个阵列的相对性能。该提案的更广泛影响来自环境地震噪声技术的方法和实施的改进，并将其扩展到地震体波成像。将利用已部署的地震台站开展K-12活动和展览，使年轻学生了解地震学的最新发展，包括记录环境地震噪声和地震P波尾波，利用环境噪声和地震P波尾波的自相关研究体波地震干涉测量法，以获得地壳反射率。环境噪声的自相关叠加导致实际上重合的源和接收器以及有效的零偏移距反射地震道。环境噪声分布对自相关叠加的影响可以通过对单个三分量台站进行极化分析来近似估计，但更全面的分析可以通过使用小型地震台阵的波束形成来完成。将在以Earthscope地震台站SFIN为中心的10公里螺旋臂阵列配置上部署12个便携式地震台站，为期数月，并将进行波束形成，以估计自相关环境噪声信号的区域照明分布，从而获得照明校正。然后将这些方法应用于中西部中部上部具有类似环境噪声特征的选定地震台站，以检验方法的一致性，并获得地壳反射率的有效零偏移线性剖面。几种自相关技术进行了研究，以提供更高的分辨率估计地壳反射率，包括调谐的时间和频率归一化，相位相关性，和相关的环境噪声的时频相位加权叠加。相关的P波尾波的区域性地震和余震也进行了研究，其中叠加事件被用来减少源侧散射的影响，以更好地成像接收器侧地壳。研究人员将把这个阵列与俄克拉荷马州的大N IRIS社区波场实验进行比较，以估计自相关环境噪声的虚拟地壳反射率。这个奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

This project develops new methods for exploring how to use noise in seismic measurements to better image the Earth's crustal structure. These new methods are important since many areas of the world are aseismic and controlled man-made seismic sources are expensive. So new ways to use existing nonseismic signals, called ambient noise, to image the Earth can be used in many places, such as the Midwest. Twelve portable seismic stations will be deployed centered on the Earthscope seismic station SFIN over a several month period. These methods will then be applied to selected seismic stations in the upper part of the central Midwest with similar ambient noise characteristics to test the consistency of the approach and image a stretch of the crust from Iowa to Ohio. They will compare this work by doing the same for a the recent "Large-N" IRIS Community Wavefield Demonstration Experiment in Oklahoma. Since the Oklahoma array is comparable in aperture to the small-scale array at SFIN, the relative performance of the two arrays will be compared. The broader impacts of the proposal come from improvements in the methodology and implementation of ambient seismic noise technologies and extending these to seismic body-wave imaging. Utilizing the deployed seismic stations, K-12 activities and displays will be developed to engage younger students with recent new developments in seismology, including the recording of ambient seismic noise and P-wave coda from earthquakes.Seismic interferometry for body-waves is studied for crustal reflectivity using autocorrelations of ambient noise and the P-wave coda from earthquakes. The autocorrelation stacks of ambient noise results in virtually coincident sources and receivers and effective zero-offset reflection seismic traces. The influence of the ambient noise distribution on the autocorrelation stacks can be approximately estimated using polarization analysis on single three-component stations, but a more comprehensive analysis can be done using beamforming from a small seismic array. Twelve portable seismic stations will be deployed over a 10-km spiral-arm array configuration centered on the Earthscope seismic station SFIN over a several month period, and beamforming will be performed to estimate the regional illumination distribution of the autocorrelated ambient noise signals to obtain illumination corrections. These will then be applied to selected seismic stations in the upper part of the central Midwest with similar ambient noise characteristics to test the consistency of the approach and to obtain an effective zero-offset linear section of crustal reflectivity. Several autocorrelation techniques are investigated to provide higher resolution estimates of crustal reflectivity, including tuned temporal and frequency normalizations, phase correlations, and time-frequency phase weighted stacks of the correlated ambient noise. Correlated P-wave coda of regional and teleseismic earthquakes are also investigated, where stacking over events are used to reduce the effects of source side scattering to better image the receiver side crust. The researchers will compare this array with the Large-N IRIS community wavefield experiment in Oklahoma for for the estimation of virtual crustal reflectivity from autocorrelated ambient noise.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.