2023-12-01 12:55:43
“The fault was not really known or mapped. There are very old scars in France, it is difficult to know which ones are active or can be reactivated,” explains seismologist Clément Perrin*. Six months after the violent earthquake that struck La Laigne, Cram-Chaban and the surrounding communities in Charente-Maritime and Deux-Sèvres, this scientist and his peers continue to “scan” the thousands of accumulated data. In the aftermath of this earthquake and the following days, nearly a hundred seismometers were buried in the region in order to measure soil movement for one to four months. Their analysis made it possible to identify nearly 600 replicas during this period. “Half of them happened in the very first few days. A handful reached a magnitude between 2 and 3, but most were 1 or less than 1,” explains Clément Perrin. The earthquake of June 16, at 4:38 p.m., was measured at 4.9 on the moment magnitude scale – a more reliable scale than the Richter scale.
Public meeting in Cram-Chaban on January 12
The strongest aftershock was measured at 3.9 on the very night of the earthquake, around 4:30 a.m. Seismologists have since refined their data and located “the structure” of the earthquake between Mauzé-sur-le-Migon and La Laigne over nearly two kilometers in length, in a north-south axis and at a depth between 2 and 5 kilometers. Can a similar event happen again in the short term? “Impossible to say. It is very difficult to predict the unpredictable”, summarizes Clément Perrin, describing the earthquake of June 16 “unusual and likely to occur every 50 to 100 years”.
Regularly questioned about the impact of “mega-basins”, this seismologist also looked into this “legitimate question”. Several works linked to drilling and intended for intensive irrigation of crops have actually been built in recent years in the sector, the latest being those of Mauzé-sur-le-Mignon and Sainte-Soline. “Scientifically, these volumes of water and the stresses (such as weight) they cause on the soil cannot alone generate an earthquake of 4.9 on the moment magnitude scale. The earthquake also occurred at depth, in a granite base while most of the region’s water tables are located well above, in limestone. On the other hand, did these basins play a catalytic role? We don’t know that,” says Clément Perrin, who intends to continue his work.
The results aggregated by seismologists since the earthquake of June 16 will be presented to the inhabitants of Charente-Maritime and Deux-Sèvres during a public meeting organized in Cram-Chaban on January 12.
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