Fig. 8: Schematic illustration of the triggering mechanisms of induced seismicity.
a–c Evolution of pore pressure, poroelastic stress and shear-slip stress transfer, respectively, before, during and after injection in a simplified generic fault network. The black dot in the center represents the injection well. d–f Mohr circles illustrating the stress state of the faults at each stage. a At initial conditions, faults F1 and F2 undergo right-lateral slip while fault F3 undergoes left-lateral slip (dashed arrows), in accordance with the maximum (σH) and minimum (σh) horizontal stresses. b During injection, pore pressure diffuses in the vicinity of the well. Poroelastic stressing extends farther and faster, and it exerts an inversed stress than the initial shear stress on F2 and F3, which are thus stabilized during injection. Combined with pore pressure, poroelastic stressing triggers the reactivation of F1, with the decrease of normal stress and the increase of the shear stress (e). Subsequently, F1 is stabilized by the shear stress drop (c and f). After the stop of injection, the pore pressure front continues to diffuse, while poroelastic stress relaxes (c). This change of direction leads to the increase of shear stress at the previously stabilized F2 and F3, which reach the failure envelope (f). The shear-slip stress transfer due to the reactivation of F2 affects F3, emphasizing the poroelastic effects until reaching failure.
