2. Definitions

An earthquake translates on the surface into ground vibrations. It is caused by the fracturing of rock at depth. This fracturing is due to a large accumulation of energy that is released, creating faults, when the mechanical breaking point of the rock is reached.

The earth's surface is made up of a dozen large chunks. These are the tectonic plates. They fit together like pieces of a jigsaw puzzle to form the Earth's surface envelope. These plates move by a few centimetres a year. The movement of the plates in relation to each other creates local friction, forcing them to deform. They therefore accumulate energy until they suddenly rupture. This is the earthquake (CEA definition).

On the surface, abrupt ground movements can have amplitudes of several decimeters, strong accelerations sometimes exceeding 1 g (g being the acceleration of gravity)...