n | ℓ | m |
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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 example. The motion of the surface of the Earth can be recorded by seismometers as a function of time. Then the frequencies of the free oscillations of the Earth can be calculated (Fourier transform). Measuring and modeling these frequencies help understand the inner structure of the Earth.

The true amplitude of the oscillations is small. It is greatly exaggerated here to make them easier to see.

Controls are located in the left panel. Animations are loaded when clicking on the numbers in the table or when clicking the checkboxes.

- S/T is used to choose between the spheroidal and torsional oscillations.
- view is used to switch between the full or cut 3D views.
- alt allows to show the second degenerate mode when it exists (m ≠ 0).

These animations were created to *illustrate* the free
oscillations of the Earth.
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 isotropic material, i.e., that it is made of the same material everywhere. This is wrong. The mass density and sound speeds which were used are averaged values. The calculation can be reproduced with the calculator for an isotropic sphere. Other refinements (gravity, Coriolis, ...) were not taken into account either. Earth non-sphericity was introduced to partially lift the m degeneracy.