There has probably not prevented the Bretons of sleep. An earthquake of magnitude 3 on the Richter scale was measured at 00: 21 in the night from Tuesday to Wednesday, about twenty miles from Brest (Finistère), according to the statement. According to the data of the RéNaSS, the national Network of seismic monitoring, the epicenter was located at 13 km depth in the area of the peninsula of Crozon, south of Brest.
The earthquake of the night of Tuesday to Wednesday measured to the south of Brest (screenshot).
shortly before 11 o’clock on Wednesday, at 10: 56, a new earthquake occurred in the western part of the country, this time in the area of Bordeaux (Gironde). It has otherwise been felt by the inhabitants, the RéNaSS that have measured a magnitude of 4.9, according to South-West. Although lighter, the shaking observed on that night in Britain testifies, the seismicity typical of the region, that its inhabitants know each other well. “Brittany is the third seismic region in metropolitan France,” said The Express, Olivier Dauteuil, director of research at the CNRS and tectonicien, behind the Alps and the Pyrenees. A seismicity real, but limited risks.
5,4 on the Richter scale at Hennebont
fifty earthquakes are measured on average every year in Britain, explains the specialist. The magnitude measured oscillates in general between 2.5 and 3.5 on the Richter scale, with more rare shaking “around 4.5”, explains Olivier Dauteuil. According to the data of the RéNaSS consulted by Ouest-France in September 2018, more than 700 earthquakes of a magnitude greater than 2 have been measured in the west of France since the year 2000. Britain is concerned, although a more high seismic activity is observed along the shear south-armorican, “a large geological structure that can be located in Douarnenez in Nantes”, explains the director of research. “These are geological structures of old-about 300 million years ago and are re-enabled,” he continues, pointing out that the origin of these earthquakes is not stopped to this day, and several models coexist.
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The tremor, the strongest measured in Britain in recent years dates back to the year 2002. On 30 September, an earthquake with a magnitude of 5.4 has thrilled the inhabitants of Hennebont (Morbihan). Other phenomena beyond the level 4 have been measured in recent years, according to the inventory of the Telegram, as the November 21, 2013 near Vannes (4.6) and the October 11, 1995 near Quimperlé (4,4). In July 2014, a tremor measured at the time 4.9 on the Richter scale was felt off the coast of the channel island of Jersey.
The assumption of a larger earthquake
“beyond a magnitude of 4, the quake begins to be felt”, note Olivier Dauteuil. “There may be falling objects.” From 5, the damage can be significant. But no reason to worry about an earthquake such as those measured most of the time in Britain. “Below 4, there is no danger and most are not felt,” says the tectonicien. Even in the event of jolts, more important, adds the specialist, if it is necessary to be cautious in areas where one can produce rock falls, “these earthquakes can not break a natural structure if it is not already weakened.
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For all that, “the hypothesis of a larger earthquake cannot be ruled out, warns Olivier Dauteuil. Since 1900, according to Ouest-France, the Office of Geological and Mining Research has counted six earthquakes of intensity in the epicentral 5.5 or higher, a different system of measurement than the Richter scale that goes up to the number 12. Two earthquakes of level 7 were measured in 1930 and 1959. This last jolt, tells the regional newspaper, would have been felt all the way to Paris.