Dynamic modeling of seismicity triggered by underground CO2 injection and impact on surface structures and human perception

We have conducted coupled fluid flow and geomechanical analysis of fault reactivation induced by underground CO2 injection, including dynamic analysis of fault slip, wave propagation and ground motions. We analyze the ground-motion results in terms of the potential for damage to ground surface structures and nuisance to the local population. Our modeling approach is to join coupled fluid flow and geomechanical numerical codes and theories from seismology to assess the magnitude of the seismic events generated by the simulated fault reactivation. We used a strain-softening fault constitutive model to simulate sudden, dynamic fault rupture, and to provide a source for wave-propagation and ground-motion calculations. We simulated an injection-induced small magnitude (Mw = 3) event at a hypocenter depth of about 1000 m. We then used the resulting ground-motion wave train at several monitoring stations in an inverse analysis to estimate source parameters (moment magnitude, rupture dimensions and stress drop), achieving good agreement and verification of our modeling approach. We then analyzed the results in terms of peak ground acceleration (PGA), peak ground velocity (PGV) and frequency content, with comparison to U.S. Geological Survey's instrumental intensity scales for earthquakes and the U.S. Bureau of Mines' vibration criteria for cosmetic damage to buildings, as well as human-perception vibration limits. Our results confirm the appropriateness of using PGV (rather than PGA) and frequency for the evaluation of potential ground-vibration effects on structures and humans from shallow injection-induced seismic events.