# Theoretical Geophysics – Niels Bohr Institute - University of Copenhagen

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# Theoretical Geophysics

Oil- and gas deposits are rarely detected on geophysical readings done at earth level, but the porosity - the cavities between the rock formations – of the oil/gas-reservoirs can be registered by seismic records. The researchers develop methods to dissolve the finest and thinnest layers in the underground by the help of artificial earth quakes created by powerful jets of air. Their methods are used by the oil companies when they search for deposits.

Inverse (backwards) problems are the mathematical problems one encounters when trying to create pictures of the inner structure of physical objects using measurement data. If for instance you want to create a picture of the inside of the earth by letting computers evaluate the seismograms that are registered after big earth quakes, or you want to compute a precise picture of the human brain based on medical scans. The problem is that there are numerous comparables with a large number of unknowns and that the figures in the comparables are unreliable because of the reading noises. Some inverse problems are linear, they resemble the comparables that we learn in school that is. But the non linear problems are far more complicated, and only in recent years have researchers found a method of solving them.

The history of the formation of the moon has left its imprints on the lunar surface where the composition of the different rock formations gives a hint of which processes dominated at the time of its birth. But even so it has not been possible completely to confirm the theory that the moon was created by a gigantic collision between the previous earth and a Mars like planet. The geophysicists have therefore availed themselves of modern computers and methods of calculations to map out the division of layers in the deep inside of the moon in order to throw light on the collision theory.

The magnetic field of the earth originates from flowing liquid iron in the centre of the earth and shields any living thing from the destructive effect of the cosmic radiation. The researchers employ satellite readings of the slow changes of the magnetic field to reconstruct and to predict future changes in the shielding effect of the magnetic field.