Date of this Version

9-19-2022

Comments

This practical research report was submitted to the faculty of Purdue University in partial fulfillment of the requirements for the Geodata Science for Professionals Master of Science degree.

Related: Mitchell A. Spangler, Robert L. Nowack; Seismic Interferometry Applied to Wind Farm and Other Anthropogenic Noise Sources. Seismological Research Letters 2022; doi: https://doi.org/10.1785/0220220201

Abstract

We investigate seismic noise from anthropogenic sources, in particular wind turbines, for seismic interferometry. The data is from the 17-station Autocorr Seismic Array located in the Midwestern United States. The array has a linear component that extends about 30 km from north to south and a subarray to the south with a diameter of 10 km. The array was deployed from August 2019 to July 2020, which included the initial months of the Covid-19 pandemic. The northernmost seismic stations of the array are located within the southern end of one of the largest onshore wind farms in the world. To the south of the array there are regularly occurring east-west running trains. However even during times when trains are present, the frequency signatures of the wind turbines are dominant over much of the array, including seismic stations well to the south of the wind farm. Although there is vehicle traffic in the region, time windows in the late evening and early morning were chosen to reduce its effect. Shallow refraction data are available nearby individual seismic stations of the array, and since the spectral peaks do not vary for stations with differing basement depths, they are inferred to be source effects of wind turbines. When utilizing seismic interferometry, coherent Rayleigh wave signals are observed for time windows of seismic noise as short as 15 minutes. There are also concurrent estimates of average hourly wind speeds and wind gusts at the locations of the seismic stations. These data show that for ambient noise correlations, clear south propagating Rayleigh waves are observed for moderate to large average hourly wind speeds. For lower wind speeds, less coherent Rayleigh wave signals are observed in the one-hour ambient noise correlations. For seismic stations within the wind farm, both north and south propagating Rayleigh waves are observed in the correlations. However, for seismic stations to the south of the wind farm, only south propagating waves are observed, which are inferred to be coming from the wind farm.

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