Evidence of wind turbines as a metamaterial-like urban layer: Monitoring of the seismic wavefield by Distributed Acoustic Sensing

The deflection and the control of the effects of the complex urban seismic wavefield on the built environment is a major challenge in earthquake engineering. The interactions between the soil and the structures and between the structures themselves strongly modify the lateral variability of ground motion seen in connection to earthquake damage, meaning that the urban environment must be considered not only as a passive receiver, but as an active source of seismic energy. In a large-scale experiment, we have investigated the idea that flexural and compressional resonances of a large number of neighbouring wind turbines strongly influence the propagation of the seismic wavefield. We can demonstrate that surface waves are strongly damped in several distinct frequency bands when interacting at the resonances of a set of wind turbines. The ground-anchored arrangement of these turbines produces unusual amplitude and phase patterns in the observed seismic wavefield. By using Distributed Acoustic Sensing it is possible to map the spatially varying ground motion and to confirm that the mechanical resonances are responsible for the strong coupling between the wind turbines and the seismic wavefield observed in certain frequency ranges of engineering interest.