Relocation of clustered earthquakes in the Groningen gas field. Issue 5 (17th January 2018)

• Record Type: Journal Article
• Authors: Jagt, Lisanne; Ruigrok, Elmer; Paulssen, Hanneke
• Is Part Of: Geologie en mijnbouw. Volume 96:Issue 5(2017)
• Page Start: s163
• Page End: s173
• Publication Date: 2018-01-17
• Subjects: Groningen, -- induced seismicity, -- multiplet analysis, -- relocation; Geology -- Periodicals; Geology -- Netherlands -- Periodicals; Mines and mineral resources -- Periodicals; 551.05
• DOI: 10.1017/njg.2017.12
• Languages: English
• ISSNs: 0016-7746

Abstract

Abstract: 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.