Fig. 7: Conceptual illustrations of causal mechanism.
From: Causal mechanism of injection-induced earthquakes through the Mw 5.5 Pohang earthquake case study
Red areas represent pore pressure increase from fluid injection. Superimposed on the pore pressure cloud is the Coulomb static stress. The black line is a fault with sense of slip shown with arrows and earthquakes are indicated by small dots outlined in yellow. Dashed white contour is a pore pressure contour of constant magnitude. Elapsed time since start of injection increases from first to third row. a Pore pressure increase after a period of constant injection with the start of induced seismicity. b Mohr–Coulomb diagram showing triggering due to increased pore pressure along a preexisting critically stressed fault. c Pore pressure increase continues to expand following cessation of injection and more earthquakes are induced. d Mohr–Coulomb diagram showing triggering due to increase of differential stress along the fault. e High pore pressure increase starts to dissipate, but moderate pore pressure increase continues to diffuse away from well, and earthquakes continue and a larger event occurs (white star). f Mohr–Coulomb diagram showing triggering caused by weakening of the fault due to reduction of the coefficient of friction and reduced cohesion42.
