Gravity is ruled by mass. As mass goes, so goes gravity. Earth's mass is heterogeneous and unevenly distributed. Contrary to the notion of a static terra firma, the distribution of mass changes over time.
Gravity Recovery and Climate Experiment visualizations of the Earth show variations in Earth's gravitational field. Color zones (right) indicate gravity anomalies where gravity is stronger or weaker than it would be if Earth was a perfectly smooth sphere with homogeneously distributed mass.
The continental spine of the Andes represents an aggregation of mass and a corresponding but imperceptibly stronger gravitational pull indicated by the deep red-colored zone along the coast of South America.
Large earthquakes deform Earth's crust creating local variations in gravity.
The blue zone in the image below shows a weaker gravity deviation, or gravity scar, near the 9.0 magnitude earthquake that struck in the Pacific Ocean east of Honshu Island in March 2011.
|Gravity scar following Honshu earthquake|
It must have appeared almost as improbable to the earlier geologists, that the laws of earthquakes should one day throw light on the origin of mountains, as it must to the first astronomers, that the fall of an apple should assist in explaining the motions of the moon.
― Charles Lyell, Principles of Geology, Volume 3, 1833.
- Earth's Gravity Scarred by Earthquake, ESA. 3 December 2013.
- Gravity Recovery and Climate Experiment (GRACE).
- Principles of Geology, Volume 3, Charles Lyell, 1833, London.