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

该项目开发了探索如何在地震测量中使用噪声来更好地成像地球地壳结构的新方法。这些新方法很重要，因为世界上许多地区都是地震地区，而可控的人造地震震源是昂贵的。因此，利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，比如中西部。12个便携式地震台站将在几个月的时间内以地球范围地震台站SFIN为中心部署。然后，这些方法将被应用于中西部中部上部具有相似环境噪声特征的选定地震台站，以测试方法的一致性，并对从爱荷华州到俄亥俄州的一段地壳进行成像。他们将通过最近在俄克拉何马州进行的“大n”IRIS社区波场演示实验来比较这项工作。由于俄克拉荷马阵列的孔径与SFIN的小型阵列相当，因此将比较两种阵列的相对性能。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。利用部署的地震台站，将开发K-12活动和展示，以吸引年轻的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的p波尾波。利用环境噪声和地震p波尾波的自相关性，研究了体波干涉测量地壳反射率的方法。环境噪声的自相关叠加产生了几乎一致的震源和接收机以及有效的零偏移反射地震道。环境噪声分布对自相关叠加的影响可以通过单台三分量台站的极化分析来近似估计，但更全面的分析可以通过小型地震阵的波束形成来完成。在几个月的时间里，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，并进行波束形成，以估计自相关环境噪声信号的区域光照分布，从而获得光照校正。然后将这些方法应用于具有相似环境噪声特征的中西部中部上部的选定地震台站，以测试方法的一致性，并获得有效的零偏移地壳反射率线性剖面。研究了几种自相关技术，以提供更高分辨率的地壳反射率估计，包括调谐时间和频率归一化、相位相关和相关环境噪声的时频相位加权叠加。本文还研究了区域地震和远震地震的相关纵波尾波，其中使用事件叠加来减少源侧散射的影响，从而更好地成像接收侧地壳。研究人员将把这个阵列与俄克拉何马州的大n IRIS社区波场实验进行比较，以便从自相关环境噪声中估计虚拟地壳反射率。该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。

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.