relation: https://episodesplatform.eu/eprints/2051/ title: Relocation of clustered earthquakes in the Groningen gas field creator: Jagt, Lisanne creator: Ruigrok, Elmer creator: Paulssen, Hanneke subject: Groningen subject: Clustering and migration subject: Conventional hydrocarbon extraction subject: Unconventional hydrocarbon extraction description: 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. publisher: Cambridge University Press date: 2017 type: Article type: NonPeerReviewed identifier: Jagt, Lisanne and Ruigrok, Elmer and Paulssen, Hanneke (2017) Relocation of clustered earthquakes in the Groningen gas field. Netherlands Journal of Geosciences, 96 (05). s163-s173. DOI: https://doi.org/10.1017/njg.2017.12 relation: http://doi.org/10.1017/njg.2017.12 relation: doi:10.1017/njg.2017.12