The department of Charente-Maritime in western France experienced its second earthquake in less than three weeks on Saturday.
The earthquake registered at a fairly low 3.6 on the Richter scale and hit on Saturday morning, with the epicentre located in the town of Jonzac.
The previous earthquake, measuring 4.9 on the Richter scale, hit the area on March 20th about 20 km to the south of Jonzac in Montendre and could be felt all the way from Bordeaux to the city of Poitiers in western France.
But how much should those who live in Charente-Maritime be concerned by these two earthquakes?
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Expert Gilles Mazet-Roux from France's Atomic Energy Commission (CEA) told The Local that two earthquakes occurring so close to one another should not come as too much of a surprise.
“The second earthquake is what we call a replica of the one on March 20th,” he said, adding that the first one was 30 times larger.
“It's a classic situation that we see in the days following an earthquake. More earthquakes occur after the initial hit and then these become less and less frequent,” he said.
“I believe there were two more on March 20th and another on March 29th.”
So, why does this happen?
“The first shock would have altered the subterranean balance, led to turbulence, and there can still be 'mood swings' in the area,” Christophe Sira from France's Central Bureau of Seismology (BCSF) told the French press.
On Saturday, the earth slipped and moved a centimetre, Sira said, adding that this wave of movement spread about 50 kilometres while the earthquake of March 20th moved the earth around four centimetres.
And should people in Charente-Maritime be worried?
While it is “relatively rare” to see earthquakes in the Charente-Maritime department, which is located in Nouvelle-Aquitaine, it wasn't a “total surprise”, said Mazet-Roux from the EMSC.
“There have been others and there will be again but it is not that common,” he added.
Meanwhile Sira from the BCSF described the area as “one of the most stable zones of France”.
However he added that this doesn't mean the area won't experience another, perhaps more intense, earthquake in the future.
Map: European-Mediterranean Seismological Centre (EMSC)
However he said that even this shouldn't be too much cause for concern, explaining that France will never experience a “big one” of the likes expected to occur in California in the coming years or indeed like the one which occurred in Sumatra in Indonesia in 2004, killing 250,000 people.
“This is for the simple reason that we have no 'fault' of this size,” he said, referring to the thin zone of crushed rock in the earth's crust which, when one slips against another, leads to earthquakes.
Metropolitan France, which is located in the middle of the European tectonic plate – away from big 'faults' – is not affected by more serious intercontinental shocks.
The bad news is that even if an earthquake can be deadly even if they do not reach a high number on the Richter scale.
For example, in 1909, one estimated at 6.2 in Lambesc in the department of Bouches-du-Rhône in southern France destroyed five villages and killed about 50 people.
Since the beginning of 2019, 25 earthquakes have been recorded by the French central seismological office (BCSF) however among these only ten to 15 have been felt by the population.
And on average there are 2,500 earthquakes per year in metropolitan France.
The infographic from Le Parisien below shows where some of the most significant earthquakes in France have taken place in recent years.
Deux séismes en trois semaines en Charente-Maritime : ces secousses ressenties récemment >> https://t.co/hTIqerNYHQ pic.twitter.com/4PH3fDbkQe
— Le Parisien Infog (@LeParisienInfog) April 7, 2019
In France, the most sensitive areas are found around the Pyrenees and in the countryside around the German border and in the Alps.
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