Free oscillations of the earth


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Click a cell in the table to start. See help below.


This page presents some animations of the free oscillations of the Earth. These oscillations get excited by earthquakes for examples. The movements of the surface of the Earth can be recorded by seismometers as a function of time. Using such records, the frequencies of Earth free oscillations can be obtained (Fourier transform). Measuring and modeling these frequencies help us understand the inner structure of the Earth.

The true amplitude of the oscillations is less than one millimeter and it has been greatly exaggerated to make it easier to see.


Controls are located in the left pane. Animations can be loaded using the numbers in the table and the checkboxes.


These animations were created to illustrates the geometry of Earth free oscillations and this doesn't require a very accurate model. The periods which are displayed come from real measurements.

The model used for calculating the animations assumes that the Earth is made of an homogeneous material, i.e. that it is made of the same material everywhere. This is wrong and the mass density and sound speeds which were used are averaged values. Other sophistications such as gravity and the Coriolis effect were not taken into account either. Earth non-sphericity was introduced to partially lift the m degeneracy.


Earth map from NASA. The animations were computed using POV-Ray.