Mechanism and implications of shut-in induced earthquakes

Abstract

Fluid pressurization rate is an important inducement to fracture slip. In order to characterize 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 cannot 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 fluctuating pressure generated from injection wells or underground water sources around fault. Furthermore, 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.

Keywords

• Shut-in induced earthquake
• Fluid pressurization rate
• Fluid pressure non-uniform distribution
• Fracture surface evolution
• Fluid pressure gradient