While the supercritical Co2 injection technology has been successfully employed for utilization operations such as enhanced oil recovery, there are some social and technical challenges with its large-scale implementation for storage purposes. Induced seismicity due to Co2 injection is one of primary concerns associated with the technology and it needs to be properly addressed. In this study, a set of 2D coupled Thermo-Hydro-Mechanical (THM) modeling was performed to investigate the effects of the reservoir porosity and thickness on the magnitude of induced seismic events. The model included a limited-dimension pre-existing fault which cannot be easily detected by geophysical surveys. The numerical modeling was used to simulate changes in the stress distribution in the reservoir, fault and surrounding rock due to Co2 injection. The fault slip obtained from the model was then correlated to the magnitude of earthquake for each case. Three reservoir thicknesses and three reservoir porosities were examined in parametric studies. The results showed that thin reservoirs have higher probability of failure and will result in larger-magnitude induced seismic events. Reservoirs with higher porosity were shown to have longer rupture time and larger events.