Mechanism and implications of shut-in induced earthquakes

Fluid pressurization rate is an important inducement to fracture slip. In order to char-acterize the fracture slip initiation and slip mode during fluid pressurization, a series of stepwise injection induced shear tests were carried out. Results show that fracture slip initiation depends on fluid pressure and roughness of fracture surface. Fluid pressurization rate, fluid pressure non- uniform distribution all affect fracture slip initiation. Reducing fluid pressurization rate seems can-not effectively avoid induced earthquake, but can delay the time and scale of induced earthquake, especially can alleviate induced earthquake after shut-in. Earthquake induced after shut-in may be caused by secondary damage of concave-convex body on fault surface under the action of fluctuat-ing pressure generated from injection wells or underground water sources around fault. Further-more, a new view is proposed that the change of fluid pressure gradient on fracture surface is an important complementary mechanism for shut-in induced earthquakes. (c) 2022 THE AUTHORS. Published by Elsevier BV on behalf of Faculty of Engineering, Alexandria University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).