Bouguer platter

The bouguer plate is a model of gravimetry used to obtain the bouguer anomaly . The gravity measurements are corrected to a reference level in order to enable different measurements to be compared. The Bouguer plate is an infinitely extended plate of the thickness between the measuring points and the reference level. The acceleration of gravity on this plate acts perpendicularly and its density is homogeneous .

The simple Bouguer plate can be chosen flat or spherical , depending on the model and neglects the influences of the topology . The complete Bouguer plate includes influences of the topology.

Basics

The mathematical basis of the Bouguer plate is the vertical component of the gravitational acceleration . This is applied to an infinitely extended layer of thickness h: ${\displaystyle g}$

${\displaystyle \delta g_{B}=2\pi \cdot G\cdot \rho \cdot h}$

In this formula is

• G is the gravitational constant
• ${\displaystyle \rho }$the average rock density of the plate; usually is assumed. ${\displaystyle \rho =2670\,\mathrm {\frac {kg}{m^{3}}} }$

So you get an average correction of

${\displaystyle \Rightarrow {\frac {\delta g_{B}}{h}}=2\pi \cdot G\cdot \rho =0,1119\,\mathrm {\frac {mGal}{m}} }$

application

The Bouguer plate can be used for land measurements and marine measurements.

Land survey

The mass excess of an infinitely extended plate is subtracted from the measurements. The density of the Bouguer plate is deduced from the local geology . The Bouguer anomaly is obtained from this correction. In the case of a mass excess, a positive bougueranomaly is obtained.

Marine measurement

The sea ​​level is chosen as the reference level . In this case, the open air anomaly and the bouguer anomaly are identical. A reduction to a reference level is unnecessary. However, an inverse bouguer plate is used because the density of the water is lower than that of the crust. The missing mass is compensated between the sea ​​floor and the reference level. The bathymetry has a great influence on the measurement. For this reason, the complete bouguer plate is preferred.

literature

• Geldart Telford: Applied Geophysics. Cambridge University Press, Cambridge 1990, ISBN 0-521-32693-1
• Thorsten Dahm: Lecture notes: Introduction to geophysics. Hamburg 2007.
• The Bouguer anomaly TU Freiberg (pdf, accessed March 21, 2010; 14 kB).