Seismic Interferometry Applied to Wind Farm and Other Anthropogenic Noise Sources

Abstract

Abstract Seismic noise from anthropogenic sources is investigated using data from the Autocorr Seismic Array located in the midwestern United States. The array has a linear component that extends about 29 km from north to south and a spiral subarray component to the south with a diameter of about 10 km. A motivation of the study is to identify the dominant sources of the anthropogenic noise in the area. The northernmost seismic stations of the array are located within the southern end of a large wind farm. 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. Because the spectral signatures do not vary for stations with differing basement depths, they are inferred to be from source effects. The interferometric results show clear south-propagating waves traveling at the Rayleigh speed inferred to be from the wind farm to the north of the array for moderate-to-large wind speeds. For lower wind speeds, less coherent signals are observed in the one-hour noise correlations, and some north-propagating waves are also present. Both north- and south-propagating waves are observed in the interferometric results for seismic stations within the wind farm. For seismic stations to the south of the wind farm, mostly south-propagating waves are observed, which are inferred to be coming from the wind farm. Using the spiral subarray, beamforming results show dominant energy from the north of the array in the direction of the wind farm for moderate-to-high wind speeds. For lower wind speeds, seismic energy from the north is no longer dominant, and seismic energy from the south and east of the array also occur.