Why an earthquake like in Montelimar could take place anywhere in France without warning

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SCIENCE – This Monday, November 11th, a magnitude 5.4 earthquake on the Richter scale took place in France. Located near Montelimar, the earthquake was felt in the south-east of France, particularly in Drôme and Ardeche.

Four people were injured in the earthquake, one seriously. No impact was noted at nearby nuclear power plants. Logically, all the French seismologists and geologists have looked into this earthquake. Especially that it is quite mysterious and reminds us that a jolt of this power can happen unpredictably anywhere in France.

"Teams from Grenoble and Nice are on their way to set up seismometers around the area to record the microrepliques to better understand what happened," he said. HuffPost Jerome Vergne, School and Observatory of Earth Sciences in Strasbourg (a city where a small earthquake was felt on Tuesday).

Because for the moment, we do not really know where this earthquake comes from. "Overall, it is an event located near a fault well known to geologists, formed there are millions of years, the fault of the Cevennes," said Jerome Vergne.

An unknown fault?

Problem: The researchers wonder if the earthquake did not actually occur on another fault, unknown to scientists, that could be connected to it. "What surprised us is that we think that the fault of the Cevennes produces earthquakes," says the seismologist. Basically, it means that two blocks of rock slide horizontally relative to each other.

"But the first analyzes of the data of yesterday's earthquake show not a mechanism picking up, but a 'reverse' mechanism, with a block that shows over the other", analyzes Jerôme Vergne.

Two possibilities: either the fault of the Cevennes was poorly understood (there is also no consensus yet to know if it is still active among researchers), or the earthquake comes from another fault, still unknown until then.

Because we must remember, we do not know all the flaws in France. Rocks on the surface must be analyzed for active faults thousands of years ago. And to find the flaws still active today, it is necessary to create networks of seismometers to analyze microseisms, impossible to feel for humans.

"An earthquake similar to this one, of a magnitude of 5, can arrive in places that we did not imagine, where no fault is known", explains Jerôme Vergne. On the other hand, an earthquake of magnitude 6 or higher, which would be a major earthquake in France, is very unlikely to occur elsewhere than on a known fault. "To produce such a strong earthquake, such a fault will probably have produced other earthquakes before."

To see also on The HuffPost:



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https://www.huffingtonpost.fr/entry/pourquoi-un-tel-seisme-pourrait-avoir-lieu-nimporte-ou-en-france-sans-prevenir_fr_5dcaaaafe4b00927b2398bbe

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