The Three Sisters Volcanic Complex is located in Lane County, Oregon, and South Sister is considered an active volcano. The USGS observed gradual deformation and uplift around South Sister during 1996-1997. A previous satellite interferometry study of South Sister found that volcanic activity was ongoing during 2020-2021. The results showed that the input rate of magma into the volcano edifice decreased during 2004-2010. Seismic velocity is sensitive to the pressurization state of the system. We can correlate relative seismic velocity with GPS observations to monitor the dynamics of the subsurface of the volcano. The SeisMIC Model is a Python package that provides functionality to apply concepts of seismic interferometry to elastic wave data, reconstructing continuous Green's functions. The expected findings are the relationship between the inflation of the volcano edifice and the seismic velocity change, which could also reveal the relationship between velocity change and deformation. Seismic velocity change is not dependent on the occurrence and location of seismicity, due to its continuous nature. This study could provide a better understanding of the mechanisms causing seismic velocity changes at South Sister.