A review of mechanisms of induced earthquakes: from a view of rock mechanics

The induced earthquake recently has gained an increasing public awareness of environmental and safety issue. The earthquakes associated with fluid injection and extraction, reservoir impoundment and mining/rock removal have been extensively reported. Here, we reviewed injection induced earthquakes and their mechanisms from a view of rock mechanics. This review begins by briefly introducing the classification and the state-of-the-art research of induced earthquakes. From a view of rock mechanics, three fundamental mechanisms of induced earthquakes, i.e., pore pressure increase, stress change, and change in coefficient of friction, are introduced in details. Firstly, we discussed pore pressure increase due to fluid injection and reservoir impoundment, and explained earthquakes caused by fluid injection and related to reservoirs according to the Mohr-Coulomb failure criterion and effective stress law in the saturated rock. Secondly, we discussed stress change resulting from fluid extraction, temperature change, reservoir loading and quarry unloading. Thirdly, we investigated factors determining coefficient of friction, i.e., mineralogy, fluid pressure and temperature. Moreover, it is a remarkable fact that additional physical or chemical effects of fluids may lead to weakening of materials in fault zones owing to stress corrosion and stable slip, according to the rate and state friction law. Finally, we summarized and compared mechanisms of induced earthquakes that occurred in a variety of past human activities and projects, and recommended future potential means and scopes to investigate the mechanism of induced earthquakes.