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Induced Repeating Earthquakes: An Indicator for Pore Pressure Changes?
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, Fifth EAGE Passive Seismic Workshop, Sep 2014, Volume 2014, p.1 - 5
Abstract
We propose a method to identify repeating events and apply it to microseismic data recorded during and after the stimulation of the geothermal reservoir at Basel-1, Switzerland. Our method is based on a combination of the measured waveform similarity between event pairs and an estimate of the source radii. In our case study, at least 15% of the microseismic events can be grouped into repeating earthquake sequences. We then analyse the spatial and temporal characteristics of the repeating events and find that they differ significantly from the behaviour of the entire microseismic dataset. Repeating events are a common feature during the stimulation phase and at small distances from the injection source (<250–300m), but they are clearly under-represented after the shut-in and at larger distances. The distance interval, where the behaviour of seismicity changes abruptly, correlates with the occurrence of the largest induced events (here Mw > 2.0). The observations suggest that the repeating earthquakes define a subset of seismicity which is particularly sensitive to pore pressure changes and is less affected by earthquake interaction. Therefore, the analysis of injection-induced events may provide a tool to identify the dominant triggering mechanism of seismicity and to detect possible changes of the triggering mechanism (e.g. pore pressure versus stress transfer).