Irritating earthquake sounds, reported also at low ground shaking levels, can
negatively impact the social acceptance of geo-engineering applications.
Concurringly, earthquake sound patterns have been linked to faulting
mechanisms, thus opening possibilities for earthquake source characterisation.
Inspired 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 solid Earth and the atmosphere. We assess
the sensitivity of ground shaking and audible noise distributions to the source
geometry of small induced earthquakes, using the largest recorded event in 2018
of magnitude ML=1.8. Utilizing recent computational advances, we are able to
model seismo-acoustic frequencies up to 25 Hz therefore reaching the lower
limit of human sound sensitivity. Our results provide for the first time
synthetic spatial nuisance distributions of audible sounds at the 50-100 m
scale for a densely populated metropolitan region. In five here presented 3D
coupled elastic-acoustic scenario simulations, we include the effects of
topography and subsurface structure, and analyse the audible loudness of
earthquake generated acoustic waves. We can show that in our region of
interest, S-waves are generating the loudest sound disturbance. We compare our
sound nuisance distributions to commonly used empirical relationships using
statistical analysis. We find that our 3D synthetics are generally smaller than
predicted empirically, and that the interplay of source-mechanism specific
radiation pattern and topography can add considerable non-linear contributions.
Our study highlights the complexity and information content of spatially
variable audible effects, even when caused by very small earthquakes.Comment: 29 pages, 9 figures. This paper has been submitted to the Bulletin of
the Seismological Society of America for publicatio