Recent developments in the densification of the seismic network covering the Groningen
gas field allow a more detailed study of the connection between induced seismicity and
reactivated faults around the gas reservoir at 3 km depth.

With the reduction of the average
station distance from 20 km to 4–5 km, a probabilistic full-waveform moment tensor
inversion procedure could be applied, resulting in both improved hypocenter location
accuracy and full moment tensor solutions for events of M≥2:0 recorded in the period
2016–2019. Hypocenter locations as output from the moment tensor inversion are compared
to locations from the application of other methods and are found similar within
250 m distance.

Moment tensor results show that the double-couple (DC) solutions are
in accordance with the known structure, namely normal faulting along 50°–70°
dipping faults. Comparison with reprocessed 3D seismic sections, extended to a depth
of 6–7 km, demonstrate that (a) most events occur along faults with a small throw and
(b) reactivated faults in the reservoir often continue downward in the Carboniferous
underburden. From non-DC contributions, the isotropic (ISO) component is dominant and
shows consistent negative values, which is expected in a compacting medium. There is
some indication that events connected to faults with a large throw ( > 70 m) exhibit the
largest ISO component (40%–50%).