%0 Journal Article
%@ 0016-7746
%A Jagt, Lisanne
%A Ruigrok, Elmer
%A Paulssen, Hanneke
%A Department of Earth Sciences, Utrecht University, Heidelberglaan 2, Utrecht, the Netherlands,
%A Department of Earth Sciences, Utrecht University, Heidelberglaan 2, Utrecht, the Netherlands; R&D Seismology and Acoustics, Royal Netherlands Meteorological Institute, De Bilt, the Netherlands,
%A Department of Earth Sciences, Utrecht University, Heidelberglaan 2, Utrecht, the Netherlands,
%D 2017
%F epos:2051
%I Cambridge University Press
%J Netherlands Journal of Geosciences
%K Groningen, induced seismicity, multiplet analysis, relocation
%N 05
%P s163-s173
%T Relocation of clustered earthquakes in the Groningen gas field
%U https://episodesplatform.eu/eprints/2051/
%V 96
%X Previous locations of earthquakes induced by depletion of the Groningen gas field were not accurate enough to infer which faults in the reservoir are reactivated. A multiplet analysis is performed to identify clusters of earthquakes that have similar waveforms, representing repeating rupture on the same or nearby faults. The multiplet analysis is based on the cross-correlation of seismograms to assess the degree of similarity. Using data of a single station, six earthquake clusters within the limits of the Groningen field were identified for the period 2010 to mid-2014. Four of these clusters  were suitable for a relocation method that is based on the difference in travel time between the P- and the S-wave. Events within a cluster can be relocated relative to a master event with improved accuracy by cross-correlating first arrivals. By choosing master events located with a new dense seismic network, the relocated events likely not only have better relative, but also improved absolute locations. For a few clusters with sufficient signal-to-noise detections, we show that the relocation method is successful in assigning clusters to specific faults at the reservoir level. Overall, about 90% of the events did not show clustering, despite choosing low correlation thresholds of 0.5 and 0.6. This suggests that different faults and/or fault segments with likely varying source mechanisms are active in reservoir sub-regions of a few square kilometres.