On Friday June 16, a major earthquake shook western France. Experts from the National Seismic Monitoring Network (Renass) and the French Central Seismological Bureau (BCSF) measured a magnitude of 5.3 to 5.8. The earthquake took place in Cram-Chaban (Charente-Maritime), between La Rochelle and Niort. This is the largest earthquake in this region for about fifty years and since the one recorded in Oléron in 1972.
The mechanical pressures that accumulate on the rocks at the level of plate tectonics are at the origin of this earthquake. France is concerned by the African plate which is heading towards Europe and the Italian plate which is advancing towards the interior of the Alps.
Although earthquakes are less powerful in France than elsewhere in the world, the country is subject to seismic risk. Each year, hundreds of earthquakes are recorded in the territory, but only a few are felt by the population. With magnitudes generally below 6, France is considered a country where the seismic risk is medium.
Prediction of natural disasters
It is difficult to accurately predict the occurrence of natural disasters, but new scientific knowledge allows a more precise assessment. Seismic building codes allow buildings to be designed to withstand earthquakes. Each country should have official templates for developing national risk prevention and reduction strategies.
The CRNS has developed new probabilistic models to better anticipate the risks associated with earthquakes, called ESHM20 and ESRM20. However, it is important to prepare as well as possible, to improve prevention and to minimize the harmful consequences because natural disasters are inevitable.
Regions prone to earthquakes
Some regions are more prone to earthquakes than others. Even if the probability of an earthquake is very low in the northeast, in Seine-et-Marne, in Eure or in Gironde, it is average in the southeast and in part of the southwest.
The departments of Vendée, Maine-et-Loire, Indre-et-Loire, Charente-Maritime, Charente, Vienne and Deux-Sèvres are also areas where the probability of an earthquake is mean. A few departments in the south-east, such as Ardèche and Drôme, are also included in this list.
The average earthquake probability mainly concerns the departments of Pyrénées-Atlantiques, Hautes-Pyrénées, Haute-Garonne, Ariège, Pyrénées-Orientales, Alpes-Maritimes, Hautes-Alpes, Savoie, Vaucluse and the Alpes-de-Haute-Provence.
In the Pyrenees, earthquakes are very frequent (more than 500 per year), but most do not exceed a magnitude of 3. The massif experiences a few events of magnitude 4 each year and an earthquake of magnitude 5 every 15 to 20 years on average. However, some earthquakes (much rarer) can be more intense and potentially dangerous. This has been the case several times in the past.
The earthquake that occurred in Argelès-Gazost in the Hautes-Pyrénées, with a magnitude of 4.9, remained in the memories. It had been felt as far away as Barcelona and Toulouse and had caused only slight damage in the vicinity of Lourdes (falling chimneys and brief power cuts) thanks to the depth of the outbreak (9 km) and the very sparsely populated epicenter.
The strongest historical earthquake in the region would have taken place in 1660 and would have caused several thousand deaths, with a magnitude close to 6.5. A new earthquake of this magnitude cannot be ruled out, especially in the western Pyrenees.