**6. Induced seismicity**

From a safety and public perception point of view, a more unacceptable issue for CO2 injection into the underground formation is the microseismic activity caused by fault activity or surface uplift during the injection process. Sometimes the intensity of induced seismicity will be perceived by humans. Slight shear sliding of fractures is induced when the induced seismic magnitude is very low. It will be more beneficial for CO2 injection if the fractures are confined within the reservoir, as fracture sliding enhances permeability. However, microseismicity caused by GCS is difficult to control. Seismic events which can be sensed may have serious consequences such as massive CO2 leakage, damage to injection wells, vertical surface displacement damaging buildings or infrastructure, etc. For example, several of the largest seismic events in the United States in 2011 and 2012 may have been caused by nearby disposal wells. The largest of these was a 5.6 magnitude seismic that occurred in Oklahoma, destroyed 14 buildings and injured two people. For the public, a perceptible seismic event would cause serious panic. Therefore, it is important to minimize or avoid seismic activity to ensure that geological energy projects such as GCS are carried out [39, 54–56].
