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Abstract

Seismic waves can couplewith 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,
even at low ground-shaking levels, which can negatively impact the social acceptance of
geoengineering applications.Motivated by consistent reports of felt and heard disturbances
associated with the weeks-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 based on the properties of the largest local magnitude ML 1.8 event.
Utilizing recent computational advances and the open-source software SeisSol, we model
seismoacoustic frequencies up to 25 Hz, thereby reaching the lower limit of the human audible
sound frequency range. We present synthetic distributions of shaking and audible
sounds at the 50–100 m scale across a 12 km × 12 kmarea and discuss implications for better
understanding seismic nuisances in metropolitan regions. In five 3D coupled elastic–acoustic
scenario simulations that include data on topography and subsurface structure, 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 ≤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 mechanism-
specific radiation pattern and topography can lead to significant nonlinear effects. Our
study highlights the complexity and information content of spatially variable audible effects
associated with small induced earthquakes on local scales.