Seismic Site Effects Assessment at the Illinois Basin–Decatur Project (IBDP) site

Carbon capture and storage (CCS), is key to curtail carbon dioxide (CO₂) atmospheric emissions and mitigate climate change. The complexities of carbon dioxide (CO₂) storage are deeply intertwined with induced seismicity, a phenomenon set in motion by pore pressure, temperature and stress changes occurring during CO₂ injection. If perceived, induced seismicity may negatively affect public perception of this carbon-removal technology. Here, we focus on assessing ground motion manifestations on the surface during hypothetical earthquakes with magnitudes ranging from 2 to 5, occurring at a depth of 2 km beneath the upper edge of the Precambrian basement rock of the Illinois Basin–Decatur Project (IBDP) site. The objective of this investigation is to analyze the seismic response of the IBDP site surface to earthquakes of specific magnitudes, considering their potential occurrence in connection with CO₂ storage at the gigatonne scale.

The analysis of ground motion manifestations on the surface during various earthquake scenarios of different magnitudes at the IBDP site provides valuable insights into the seismic vulnerability of the location. It allows for a comprehensive assessment of both amplification and attenuation effects, revealing how the geological and geotechnical characteristics of the subsurface rock influence ground motion. Understanding how the site responds to seismic events allows for a more accurate assessment of potential risks and vulnerabilities.

Employing the equivalent linear approach of Ground Response Analysis, we computed the Fourier amplitude spectra of seismic motions on the surface of the IBDP site for earthquakes with magnitudes 2, 3, 4, and 5. These spectra are then compared with the Fourier amplitude spectra of input motions. The Fourier amplitude spectrum illuminates how ground motion amplitude is distributed across various frequencies. We also analyze the calculated Fourier Amplitude Ratio.

Through a thorough comparison of these spectra, we explore the shifts in amplitude-frequency composition as the magnitude increases. This analysis is instrumental in identifying frequencies that gain prominence or diminish, revealing resonant frequencies and their correlation with input wave amplitude. These findings are crucial for understanding the dynamics of seismic events across different magnitudes and their environmental repercussions at the IBDP study site. Moreover, they have the potential to contribute to the optimization of practices in CCS.