- © 2015 by the Seismological Society of America
Although the phenomenon of earthquakes induced by the subsurface injection of fluids has been recognized, and the basic mechanisms understood, for many decades (e.g., Healy et al., 1968), the recent increase in seismicity associated with oil and gas development, including large damaging events (e.g., Ellsworth, 2013; Keranen et al., 2013; Hough, 2014; Rubinstein et al., 2014) makes clear the need to better understand the processes controlling such seismicity and to develop techniques to mitigate the associated seismic hazard.
The relationship of fault stress, fault strength, and fluid pressure at the onset of fault slip in the most basic form is given by the modified Coulomb criterion, (1)in which τ and σ are the shear and normal stress, respectively, acting on the fault surface, P is the pore‐fluid pressure, and μ is the coefficient of fault friction. The term (σ−P) is the effective normal stress (Terzaghi, 1925). From equation (1), a fault can be brought to a critical state through an increase of shear stress τ, a decrease of the normal stress σ, an increase of fluid pressure P, or some combination of the three. Increase of pore‐fluid pressure is the most widely cited cause of earthquakes induced by human activities (National Research Council, 2012). Consequently, investigations and models of induced seismicity have tended to focus mainly on spatial changes of fluid pressures (Hsieh and Bredehoeft, 1981; Shapiro and Dinske, 2009).
Although the immediate cause of injection‐induced earthquakes is the increase of fluid pressure that brings a fault to a critical stress state, models of the spatial changes of fluid pressure alone are insufficient to either predict or understand the space–time characteristics of induced earthquakes. Comprehensive system‐level models that couple physics‐based simulations of seismicity with reservoir simulations of fluid …