The Greenland Ice Sheet, the second largest in the world, is rapidly losing mass due to regional warming, making it a major driver of global sea level rise. This mass loss follows a clear seasonal cycle—melting in summer and snowfall accumulation in winter. While satellites like GRACE help monitor these changes, their limited resolution makes it hard to detect small-scale or short-term variations. In this study, we use seismic sensors across Greenland to track tiny changes in the speed of seismic waves beneath the ice. These changes, known as dv/v, closely match GRACE and GPS observations. We find that dv/v is also influenced by the thermal state of the ice-bed interface: in thawed areas, summer melting reduces seismic speed, while in frozen areas, summer pressure compacts the bed and increases speed. These patterns are most noticeable under thick ice. In lower-elevation zones where the ice melts from the surface, meltwater can reach the base and warm it. We also use fluid dynamics modeling to confirm that changes in basal conditions help explain the observed seismic signals.