<p>The gravitational anomaly (delta_g) changes linearly with the density contrast, and proportionally to the inverse square of depth. That's simply a version of the 'Universal Law of Gravitation'.
Here is an example for the anomaly created by an spherical anomalous spherical body with a density difference of delta_rho relative to the surrounding density. <em>G</em> is the known Gravitational Constant: </p>

<p><a href="https://i.sstatic.net/U5qGi.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/U5qGi.png" alt="From Turcotte and Schubert, 2002, Geodynamics"></a>
From Turcotte and Schubert, 2002, Geodynamics</p>

CC BY-SA 3.0
2016-03-24T05:13:51.753Z
I am not sure you are answering the question: you are referring to the absolute calculation of gravity but not the expected deviation in reference to the geoid (anomaly)
Neo
CC BY-SA 3.0
2016-03-24T07:48:59.520Z
Also de anomaly (not just the absolute value) of gravity follows the same dependence, since gravity is additive (the field produced at a given location by 2 bodies equals the addition of the two forces exerted by each body). The question does not mention geoid, which is a very different concept than gravity anomaly.
DrGC
CC BY-SA 3.0
2016-03-23T15:17:32.970Z
2016-03-30T17:40:12.673Z
2016-03-30T17:40:12.673Z
DrGC
<p>How does the gravitational anomaly measured at the Earth's surface and produced by a subsurface body depend on its depth and on the density contrast of the body relative to its surroundings?</p>

CC BY-SA 3.0
2016-03-23T11:59:45.850Z
Maybe do some reading around simple forward modeling of gravity anomalies. [I found this](https://www.ualberta.ca/~unsworth/UA-classes/224/notes224/B/224B2-2006.pdf) and it looks like a good start.
Matt Hall
CC BY-SA 3.0
2016-03-23T13:44:50.070Z
*the subsurface body* is too vague/broad
Jan Doggen
CC BY-SA 3.0
2016-03-24T07:54:06.303Z
A bit more of context in this question would be useful to the reader. What do you need this for? What do you want to understand? What do you know already?
DrGC
<geophysics><geology><structural-geology>
Gravitational Anomaly of a subsurface body
Lucian09474
# Gravitational Anomaly of a subsurface body

(Asked by: username_0 on 2016-03-23)

How does the gravitational anomaly measured at the Earth's surface and produced by a subsurface body depend on its depth and on the density contrast of the body relative to its surroundings?

**Tags:** geophysics, geology, structural-geology

> **Comments:**
> **username_1**: Maybe do some reading around simple forward modeling of gravity anomalies. [I found this](https://www.ualberta.ca/~unsworth/UA-classes/224/notes224/B/224B2-2006.pdf) and it looks like a good start.  
> **username_2**: *the subsurface body* is too vague/broad  
> **username_3**: A bit more of context in this question would be useful to the reader. What do you need this for? What do you want to understand? What do you know already?  

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## 1 answers

### Answer by username_3 on 2016-03-23. Score: 3 | Accepted answer

The gravitational anomaly (delta\_g) changes linearly with the density contrast, and proportionally to the inverse square of depth. That's simply a version of the 'Universal Law of Gravitation'.
Here is an example for the anomaly created by an spherical anomalous spherical body with a density difference of delta\_rho relative to the surrounding density. *G* is the known Gravitational Constant:

[![From Turcotte and Schubert, 2002, Geodynamics](https://i.sstatic.net/U5qGi.png)](https://i.sstatic.net/U5qGi.png)
From Turcotte and Schubert, 2002, Geodynamics

> **Comments:**
> **username_4**: I am not sure you are answering the question: you are referring to the absolute calculation of gravity but not the expected deviation in reference to the geoid (anomaly)  
> **username_3**: Also de anomaly (not just the absolute value) of gravity follows the same dependence, since gravity is additive (the field produced at a given location by 2 bodies equals the addition of the two forces exerted by each body). The question does not mention geoid, which is a very different concept than gravity anomaly.  

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