Gravity meter sensitivity to mass change in the subsurface

As generalized in this image, a gravity measurement is sensitive to a cone-shaped region of the subsurface—as depth increases, the sensitivity to individual water molecules decreases, but the region of sensitivity expands. The result is that for a given height of water-storage change, the corresponding gravity change is the same (1 meter of water=42×10^–8 meters per second squared), regardless of whether the water is stored near the land surface or at depth. The amount of gravity change is also independent of the porosity of the aquifer or soil.