Triggering of earthquakes by massive subsurface interventions: seismogenic index approach

Projecting seismicity triggered by massive subsurface geoscientific applications is a pressing practical problem. To address this issue, the probabilities of well-controlled induced seismic events and the probabilities of triggered tectonic earthquakes with runaway ruptures extending well beyond the operational underground rock volumes must be considered. I demonstrate how this approach can be implemented using the seismotectonic continuum concept and its combination with the seismogenic index model and the lower-bound statistics of the frequency-magnitude distributions of induced earthquakes. The magnitudes of large, runaway ruptures are controlled by the surrounding tectonic fault networks, which constitute the seismotectonic continuum. The frequency-magnitude distribution of earthquakes in the continuum is described by the Gutenberg-Richter statistics of the tectonic environment. The seismogenic index is a measure of the potential induced seismicity for a unit of geotechnological impact at a given location. It is similar to the Gutenberg-Richter a-value. The seismogenic index and the Gutenberg-Richter b-value are properties of the seismotectonic continuum. The probability of earthquakes increases due to subsurface activity in a confined rock volume. Estimating the parameters of the seismotectonic continuum, i.e., the b-value and the seismogenic index, requires the use of the seismogenic index formulation of the frequency-magnitude distribution. Furthermore, the use of the lower bound of the induced earthquake statistics may be necessary to account for the geometric limits of the operational domain. Using examples of large-scale hydrocarbon production, enhanced geothermal energy, and massive underground saltwater disposals, I demonstrate how these concepts can be applied in practice and useful for the design of deep geological repositories.