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Discrimination between natural and induced seismicity

Differentiation of natural and induced seismicity is difficult but extremely important. Seismic events observed in the vicinity of oil and gas operations can be induced, triggered, or natural. Currently used criteria, developed in the last century, are based on subjective comparison of injection activities and seismic rates to distinguish the natural and triggered seismicity. For example, a direct cross-correlation of earthquake and injection rates is intrinsically positive-valued because both, injection and earthquake rates, are positive. We objectively measure the potential connection between earthquake and the injection rates by a modified correlation approach. Applied to multiple case studies of clear-cut cases of induced seismicity, our method gives high cross-correlation values dominated by a positive maximum delayed typically by 12-24 hours. This delay corresponds to seismicity following the injection. On the other hand, our method exhibits no correlation for natural seismicity cases or for randomly simulated seismicity and injection. In such examples the result of the method is correlation values close to zero or oscillates between positive and negative values, typically between +0.5 and -0.5.

Station installation
Correlation of injection and seismicity.

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