Groundwater level monitoring using wind-turbine generated noise

As the international community continues to shy away from fossil fuels in order to keep the 1.5-degree goal in reach, more wind farms are installed across the world. Wind turbines are very large civil structures. For the onshore wind turbines, the average blade length is between 45 and 75 meters. The tower height is often twice the turbine length, from 90 to 130 meters. The tower diameter can be as wide as 3 meters, and the whole structure sits on a circular foundation poured with truck loads of concrete 15 to 22 meters in diameter. As applied seismologists, we are interested in the vibrations generated from the wind turbines, as well as the influences of these constant sources of vibrations on the surrounding infrastructure and the environment in general. In this abstract, we monitor vibration induced by wind farms using nodal seismometers. From a three-month-long recording, we observe 1) nearly constant modal vibration of the turbine tower, 2) turbine rotor vibration correlating with wind speed, and 3) quiet days that may correspond to rain or other weather conditions. The wind speed reduces from April 2022 to July 2022, resulting in an overall reduction of vibration energy. However, we observe an increase in the seismic resonance from the later arrivals of the autocorrelograms of the ambient seismic noise. This increase in seismic amplitude correlates well with the drop-down of the groundwater level in the region, as shown in the figure. Reduced water saturation results in a decrease in shear wave velocity, which subsequently increases the amplitude of near-surface resonance of the wind turbine vibrations. We plan to provide more detailed analysis of the wind farm vibration data during the presentation.