Free oscillations of the Earth

Control

n m

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

Presentation

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.

Usage

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

Approximations

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. Other refinements (gravity, Coriolis, ...) were not taken into account either. Earth non-sphericity was introduced to partially lift the m degeneracy.

Credits

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