Abstract
During fluid injection experiments at the geothermal site of Soultz-sous-Forêts
(France), more than 114,000 induced seismic events with magnitudes
between -2.0 and +2.9 were detected by a local downhole monitoring
network. Of these, 35,039 events are sufficiently constrained to
be located. Hypocenters align along a sub-vertical, planar structure
with the apparent width being dominated by data scattering indicating
that seismic activity predominantly occurs along a (pre-existing)
larger scale fault structure. For this scenario, we present a numerical
model to simulate hydraulic overpressures and induced seismicity
during hydraulic injection. The numerical model is based on the physical
processes of fluid pressure and stress diffusion with triggering
of the induced seismicity being controlled by Coulomb friction. Even
in its simplest form of a fault zone without any structural heterogeneity,
the numerical model reproduces typical observations at Soultz-sous-Forêts,
such as number and magnitude of induced events, hypocenter locations
(including the Kaiser effect), occurrence of post-injection seismicity,
and the largest magnitude event occurring several days after shut-in.
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