This lecture further discusses seismic and other geophysical methods used in groundwater exploration. Seismic methods involve generating shock waves to measure subsurface velocities and interpret variations in rock properties, helping to locate aquifers and geological boundaries. The lecture explains the principles of seismic wave refraction and the importance of velocity contrasts in identifying subsurface features. Additionally, it covers less common methods like electromagnetic, magnetic, gravity, and radiometric techniques, highlighting their applications in supplementing primary methods and detecting groundwater-related features. The lecture concludes with an overview of NASA's GRACE mission, which measures changes in Earth's gravity field to estimate groundwater storage variations over time.