Abstract

Induced seismicity from gas production has been identified as a significant problem within the Groningen Field, located in the northeast corner of the Netherlands. A key concern is the location, source mechanism, and magnitude of the microearthquake events, which are triggered by stress changes induced in the reservoir through pressure depletion. The resulting seismic energy release has been linked to building damage and social unrest in the area. The situation is compounded by the structural complexity of the subsurface with many hundreds of faults that crisscross the area, making earthquake location estimation challenging. An accurate methodology to determine both location and seismic mechanism is required. We present the results of an integrated full-waveform, 3D elastic, event location, and moment-tensor inversion workflow that has been applied to the regional, shallow borehole-monitoring array. This workflow utilizes all event arrivals to improve the accuracy of locating earthquakes and offers a reliable estimate of the earth's sense of motion during an earthquake. It is also demonstrated that the biggest source of error in locating earthquakes at Groningen lies in the vertical depth accuracy, which is correlated to the azimuthal angular coverage, and the fact that small earthquakes are only detected by a relatively small number of stations.

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