The earthquake has revived the controversy over a geothermal project carried out until last December in the north of the city and at the origin of 15 earthquakes of magnitude at least equal to 2 since November 2019.

The agglomeration of Strasbourg was awakened this Saturday by a magnitude 3.9 earthquake, the most intense in a series of tremors induced for several months by a geothermal project which continues to fuel the controversy, despite its final shutdown.

The epicenter of the earthquake that occurred at five in the morning was located five kilometers deep, in the town of La Wantzenau, north of the Strasbourg metropolitan area, according to the National Seismic Monitoring Network (Renass), who measured a magnitude of 4.0 eventually corrected to 3.9.

A magnitude 2.3 aftershock was recorded five minutes later at the same location. The two events were classified by Renass as “induced”, that is to say caused by human activity.

Faced with the intensity of the earthquake, the firefighters of Bas-Rhin announced that they had received many calls, but did not trigger an intervention. “There will be damage, but it will be on the order of cracking,” said the mayor of La Wantzenau, Michèle Kannengieser.

“Really strong”

Above all, the earthquake revived the controversy over a geothermal project carried out until last December in the north of the agglomeration, in the immediate vicinity of La Wantzenau, and at the origin of 15 earthquakes of magnitude at least equal to 2 since November. 2019.

“It was really tough this time,” tweeted Alain Fontanel, one of the opposition leaders in the Strasbourg city council. “The whole house shook for a few seconds. Thanks to the sorcerer’s apprentices of deep geothermal energy for this brutal awakening #flippant.”

Many similar reactions were visible on social media. Residents, disillusioned, have facts about the state of their homes.

“I have a recent house, built in 2007, and we had put in place a raft, a concrete slab, because it’s an area where there were upwelling,” said Francis Caspar, a inhabitant of La Wantzenau. “Today, my raft is completely cracked”.

“Regarding the highest intensity since the start of the series of induced earthquakes linked to the geothermal project, I can measure the emotion that it was able to activate”, declared the president of the Eurometropolis of Strasbourg, Pia Imbs , in a press release.

“I take this new episode which will not fail to feed the analyzes started by the information and evaluation mission installed by the Eurometropolis last December,” added the elected official close to the Greens.

“Persistent seismic activity”

“The localization and the first estimate of depth make us clearly think that these events are in the continuation of the preceding ones”, declared Jérôme Vergne, seismologist at the School and observatory of earth sciences of Strasbourg.

“We had continued to record persistent seismic activity in recent months. The subsoil encountered a certain time to react to the shutdown (of the project), and to return to a state of natural stress,” he added. “What is astonishing is that today we had the most important earthquake of the sequence”.

The Bas-Rhin prefecture announced on December 7 that the geothermal project would be definitively stopped, after a series of more or less intense earthquakes – including one of magnitude 3.5 on December 4 – and already classified as “induced” by the Renass. Fonroche Géothermie, the project leader, admitted that its activities were the source of some earthquakes. The company announced on Saturday that it had measured a magnitude 3.7 earthquake.

“These events are linked to the return to equilibrium of the reservoir which is accompanied by seismicity,” the company said in a statement.

The reservoir returned to “natural pressure” levels on April 26, according to Fonroche Géothermie, which nevertheless specifies that the pressure “continues to drop slightly”.