Density Variations of Earth Materials
Thus far it sounds like a fairly simple proposition to estimate the variation in density of the earth due to local changes in geology. There are, however, several significant complications. The first has to do with the density contrasts measured for various earth materials. The densities associated with various earth materials are shown below:
Material | Density (gm/cm^3) |
Air | ~0 |
Water | 1 |
Sediments | 1.7-2.3 |
Sandstone | 2.0-2.6 |
Shale | 2.0-2.7 |
Limestone | 2.5-2.8 |
Granite | 2.5-2.8 |
Basalts | 2.7-3.1 |
Metamorphic Rocks | 2.6-3.0 |
Notice that the relative variation in rock density is quite small, ~0.8 gm/cm^3, and there is considerable overlap in the measured densities. Hence, a knowledge of rock density alone will not be sufficient to determine rock type.
This small variation in rock density also implies that the spatial variations in the observed
gravitational acceleration caused by geologic structures will be quite small and thus difficult
to detect.
Gravity
- Overviewpg 12
- -Temporal Based Variations-
- Instrument Driftpg 13
- Tidespg 14
- A Correction Strategy for Instrument Drift and Tidespg 15
- Tidal and Drift Corrections: A Field Procedurepg 16
- Tidal and Drift Corrections: Data Reductionpg 17
- -Spatial Based Variations-
- Latitude Dependent Changes in Gravitational Accelerationpg 18
- Correcting for Latitude Dependent Changespg 19
- Vari. in Gravitational Acceleration Due to Changes in Elevationpg 20
- Accounting for Elevation Vari.: The Free-Air Correctionpg 21
- Variations in Gravity Due to Excess Masspg 22
- Correcting for Excess Mass: The Bouguer Slab Correctionpg 23
- Vari. in Gravity Due to Nearby Topographypg 24
- Terrain Correctionspg 25
- Summary of Gravity Typespg 26