The Visible Earths
01- Nazca,Cocos,Caribbean
02- Pre-Cambrian
03- Shields of the Earth
04- Shield Re-assembly
05- Volcanic Activity
06- Hinge Faults
07- Himalayas
08- Juan De Fuca, Gorda
09- Ring of Fire
10- Oceans Closed
11- Earthquake Waves
12- Mirror Plates
13- Interior
14- Continent Reflections
15- Earthquake Paths
16- Object in the interior
17- Magnetic Mirror
18- Full Expansion
19- Contraction
20- Shield Volcanoes
21- Valles Marineris
22- Entry Point of Mars
  The Gas Giants
23- The Gas Giants
24- Asteroids
25- Mercury
26- Venus' Crust
27- Gravity Anomalies
28- Free-Air Correction
29- Rudimentary America
30- Magma Oceans
31- Full Sequence & Notes

27 - Gravity Anomalies

Free-air gravity anomaly map of the earth


A gravity anomaly is the difference between a prediction of gravity and the actual observed gravity - they suggest hidden variations in the subsurface, like caves or mineral deposits.
In order to understand the anomaly a number of corrections need to be made to the measurement of gravity.

1. The theoretical gravity should be removed in order to only leave local effects.
2. The elevation of the point where each gravity measurement was taken must also be taken into account, as altitude effects the measurement of the gravity of the Earth itself. The free-air correction does this by adjusting the measurements of gravity to what they would have been if they had been measured at sea level..

When the Free-air correction is combined with the removal of theoretical gravity, this leaves leaves the free-air anomaly .

Alan Lambert 2010