Numerical simulations of seismo-acoustic nuisance patterns from an induced M1.8 earthquake in the Helsinki, southern Finland, metropolitan area

Abstract: Seismic waves can couple with the atmosphere and generate sound waves. The influence of faulting mechanisms on earthquake sound patterns provides opportunities for earthquake source characterization. Sound radiated from earthquakes can be perceived as disturbing which can negatively impact the social acceptance of geoengineering applications. Motivated by reports of felt and heard disturbances associated with the week-long stimulation of a 6 km-deep geothermal system in 2018 below the Otaniemi district of Espoo, Helsinki, we conduct fully coupled 3D numerical simulations of wave propagation in the solid Earth and the atmosphere. We assess the sensitivity of the ground shaking and audible noise distributions to the source geometry of the induced earthquakes. Utilizing recent computational advances and the open-source software SeisSol, we model seismo-acoustic frequencies up to 25 Hz, thereby reaching the lower limit of the audible sound frequency range. We present synthetic distributions of shaking and audible and discuss implications for better understanding seismic nuisances in metropolitan regions. In five 3D coupled elastic-acoustic scenario, we analyze the ground velocity and pressure levels of earthquake-generated seismic and acoustic waves. We show that S waves generate the strongest sound disturbance with sound pressure levels of up to 0.04 Pa. We use statistical analysis to compare our noise distributions with commonly used empirical relationships. We find that our 3D synthetic amplitudes are generally smaller than the empirical predictions and that the interaction of the source-specific radiation pattern and topography can lead to significant non-linear effects. Our study highlights the complexity and information content of spatially variable audible effects associated with small induced earthquakes on local scales.