You have been hired by a mining company to evaluate the results of a gravity survey taken over a potential lead mine in the Morrocan desert. Your job is to tell them how much lead there is, how much it is worth, and to recommend the next action they should take.
You will learn much more about gravity surveys in later modules. You don't need to know much about gravity for this practical, but here are a few key things:
A gravity survey measures the gravity anomaly at a point on the Earth (how much it deviates from the standard 9.81 m/s^2.
A positive gravity anomaly means that g is increased. This can be a result of many different features, including latitude, tides, nearby topography, height above sea level, and what we are interested in: near surface density changes.
A wide range of corrections are made to gravity data in order to remove the effect of these other features. Like many geophysical surveys, good quality data is the result of lots of processing.
The units of gravity surveys are reported in milli gals (mgals). 1 mgal = $10^{-5}ms^{-2}$.
The area under the curve of a gravity survey is related to the mass excess/deficit by the equation: \begin{equation} Mass \ excess = \frac{1}{2 \pi G} \times Area \ under \ curve \end{equation} ($G = $ the gravatational constant, $6.67 \times 10^{-11} m^3 kg^{-1} s^{-2}$ )
As you are now experts in finding the area under the curve, you are well qualified to calculate the excess mass, and therefore the potential profit avaliable to the mining company.
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