Abstract: Based on the U.S. Decatur CO₂ storage project, the interrelationships between the formation thickness, tectonic stress state, and microseismic activity induced by CO₂ injection during the carbon storage process were investigated in this study, providing a scientific basis for site selection and safety assessment of carbon storage. By analyzing the characteristics of the reservoir (Mt. Simon Sandstone) and caprock (Argenta Formation) thickness of the Decatur Project, the impact of these factors on pressure diffusion during injection was explored. Combining the distribution of tectonic stress and data accumulated in history, the sensitivity of fault slip in the Precambrian basement was analyzed. The Argenta Formation near the CO₂ injection point is relatively thin or absent, lacking sufficient thickness to prevent pressure migration towards the basement fault, which resulted in microseismic events occurring mostly in the Precambrian basement. After CO₂ injection into the Mt. Simon Sandstone reservoir, the pore pressure initially increased near the injection point, and then diffused over a larger area. Simple CO₂ injection alone was not strong enough to trigger large-scale microseismic activity. The Precambrian basement is more sensitive to the stress release caused by fluid injection due to the tectonic stresses accumulated in history. In the Decatur Project, when the CO₂ injection rate reached 1.25～1.4 million tons per year, fault slip and microseismic activity were induced. The selection of CO₂ storage sites should be evaluated comprehensively based on the strata thickness, tectonic stress state, and the injection-induced mechanism to ensure the safety and long-term stability of the injection.