Lecture 4 - Gravity Flashcards
What is Newton’s law for gravity?
Newton’s law for gravity states that there is an attraction between two masses, the gravitational force F, which is the product of their masses, and the distance between them.
What is the formula for Newton’s law for gravity?
F = Gm1m2/r2
(F is gravitational force, G is gravitational constant, r is the distance between them)
What is the gravitational constant?
Gravitational constant is 6.673 x 10-11 Newton
Why is latitude an important factor on the gravitational force on the Earth?
The further from the core of the Earth the lower the gravitational pull i.e. there is a greater gravitational pull at the poles than the equator.
Why are gravity surveys taken?
To measure the acceleration at the surface of the Earth. This is as acceleration is due to gravity.Measured with a gravimeter
What is meant by gravity reduction?
The correction of raw gravitational data for things such as: tide, latitude, height above sea level etc
What is the Bouguer Anomaly?
The difference between gravity that would be measured is the earth was made of made of uniform rocks, or layers of uniform density and thickness and what is actually measured at the station
How is the Bouguer Anomaly represented on a map?
A rock unit less dense than the surrounding rocks will cause a negative anomaly whereas a rock unit more dense than the surrounding rocks will provide a positive anomaly.
What are the two approaches to quantitative interpretation of gravitational data?
Forward modelling - set up a model with the best possible estimate and determine what the anomaly would be, then compare this with what is actually seen.
inverse modelling - start with what is actually measured, process this data and come up with a model of what is beneath the surface
Give examples of ways we can qualitatively interpret gravitational data
Examine contour map, profile, look for highs, lows, steep gradients, and relate these to geology map
How can gravitational data be used in relation to mineral exploration?
Can be used to detect sulphide (lead, zinc) deposits (e.g. Canada). Stronger anomaly due to lead and zinc deposits close to the surface, even stronger anomaly if more extensive sub surface deposits.
