An earthquake emits elastic energy in the form of waves (seismic waves!) that travel throughout the planet. We measure these with seismometers and derive all kinds of information from the recorded waves.
Here is how we represent the *real* data visually:
You can see these patterns… the waves travel first in one direction and then in another direction ! Why is that?
Here is a simulation of the wave propagation after the Tohoku earthquake:
but that was only two hours…
In fact, those waves keep moving– the Earth keeps vibrating for much longer than that after a large earthquake (the duration of the vibrations are proportional to the magnitude).. Here is another simulation for much longer times:
[ we need a movie of real time ! ]