What is the Bouguer gravity anomaly?
What is the Bouguer gravity anomaly?
In geodesy and geophysics, the Bouguer anomaly (named after Pierre Bouguer) is a gravity anomaly, corrected for the height at which it is measured and the attraction of terrain. The height correction alone gives a free-air gravity anomaly.
How do you interpret gravity anomaly?
Gravity anomalies, in general, are a function of horizontal variations in rock densities beneath the surface of the earth; therefore, the interpretation of gravity anomalies depends upon density contrasts. Depth-size relationships possible from geological considerations in the area involved are also necessary.
What does a positive Bouguer anomaly mean?
A location with a positive anomaly exhibits more gravity than predicted by the model—suggesting the presence of a sub-surface positive mass anomaly, while a negative anomaly exhibits a lower value than predicted—suggestive of a sub-surface mass deficit.
How is Bouguer gravity anomaly calculated?
The four basic input parameters needed to calculate a complete Bouguer anomaly are: (1) the height of the gravity station above the GRS80 reference ellipsoid, (2) the latitude of the station in WGS84 coordinates, (3) the drift- and tide-corrected observed gravity readings tied to an absolute gravity base station, and ( …
What can cause a positive gravity anomaly?
Gravity anomalies are often due to unusual concentrations of mass in a region. For example, the presence of mountain ranges will usually cause the gravitational force to be more than it would be on a featureless planet — positive gravity anomaly.
How many types of gravity anomaly are there?
It is also referred to spatially as the difference between the gravity fields observed at two points. In geophysics, there are two kinds of gravity anomalies—free air and Bouguer anomalies—depending on type of correction applied to the observed gravity field at the point of observation.
How do you pronounce Bouguer anomaly?
The Bouguer (pronounced Boo-gay´) gravity anomaly has been further corrected for the mass that may exist between sea level and the observer (a cor- rection for mass) and is a standard used in geologic interpretation on land.
What is a positive gravity anomaly give an example?
For example, the presence of mountain ranges will usually cause the gravitational force to be more than it would be on a featureless planet — positive gravity anomaly.
Are gravity anomalies real?
What does a negative gravity anomaly indicates?
deep-sea trenches These negative gravity anomalies are interpreted to mean that the segments of the lithosphere (that is, the crust and upper mantle comprising the rigid, outermost shell of the Earth) that underlie trenches are being forced down against buoyant isostatic forces.
How is bouguer correction calculated?
Bouguer correction
- δgB = Bouguer correction.
- ρ = rock density in kg/m3
- h = height difference between two locations in m.
- G = gravitational constant = 6.67384 × 10−11 m3 kg−1 s−2.
How is free air correction calculated?
ΔgELEV = -3.086h g.u. The correction, known as the free-air correction (because, in the derivation, it is assumed that the only material between the station and the reference surface is air), must therefore be positive.
