Veendam event, 09-01-2019

Most events recorded in the province of Groningen are related to compacting gas reservoirs at around 3 km depth. On January 9, 2019, a seismic event was located at the eastside of Veendam, just outside the area covered by the Groningen and Annerveen gas fields. The event was well detected up till a distance of about 15 km. The incoming waves had a character different from the typical event recorded in the area. In this report a dedicated analysis is done to further constrain the location of the event. The strong presence of guided waves point to a location near the earth’s surface. The wavetrain are much longer, however, than for an impulsive event near the Earth’s surface. The detected waveforms show similarity with a 2017 event that was located at the flanks of the Heiligerlee salt dome. Both location with a 1D optimized model and a 3D velocity model points to an event location within or at the flanks of the Zuidwending salt dome. The maximum event depth is 1275 m, as found for a P-S delay time observed at a Gasunie instrument near the event. Most likely, the event was located at the southern flank of the Zuidwending salt dome. The mechanism by which the seismic energy is generated remains to be investigated.