To assess the power of earthquakes, seismologist Richter introduced the notion of magnitude. It corresponds to the energy liberated in the focus of the seism and depends to the length of the active fault and the importance of the displacement.
|< 3.5||The earthquake is not felt, but recorded by seismographs|
|3.5 - 5.4||Often felt, but rarely causes damage|
|5.4 - 6||Slight damage to well-designed buildings, but can cause major damage to others|
|6.1 - 6.9||Can be destructive in areas up to about 100 km|
|7 - 7.9||Major earthquake. It can cause serious damage over larger areas|
|> 8||It is a very strong earthquake that can cause serious damage in areas several hundred kilometers across|
Magnitude should not be confused with intensity which is assessed from the effects produced at the surface. To estimate it, the MSK scale must be used, which name comes from its fathers Medvedev, Sponheuer and Kamik in 1964.
|Intensity||Effects produced at the surface|
|Degree I||Not felt|
|Degree II||Slightly felt|
|Degree III||Week quake partially felt|
|Degree IV||Mostly felt|
|Degree V||Wakening of sleeper|
|Degree VII||Damage to buildings|
|Degree VIII||Destruction of buildings|
|Degree IX||Damage is generalized to buildings|
|Degree X||General destruction of buildings|
|Degree XII||Landscape change|
Though the seismic activity in France is not really high, seismologists monitor the ground movement. They have in this optic seismographs that enable the record of seismic waves.
Seimology laboratories are gathered mainly in the risky zones as shown opposite.
Seismograms obtained are analyzed and used after within numerous studies like those done at TAMARIS.