On the site of the deep geothermal power plant in Illkirch-Graffenstaden, south of Strasbourg.

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G. Varela / 20 Minutes

  • The earth trembled four times during the night from Tuesday to Wednesday around Strasbourg.

  • Geothermal activities, north of the Alsatian capital, are the source of these earthquakes.

  • They have since been stopped again.

    But they should pick up one day: the State is the decision maker but the city and the Eurometropolis need this renewable energy.

“I felt it a la Robertsau, it was enough to wake me up.

Like some Strasbourg residents, Marc Hoffsess experienced the last earthquakes that hit the Alsatian capital, during the night from Tuesday to Wednesday.

Four successive, precisely at 11:33 p.m., 12:40 a.m., 5:39 a.m. and 6:18 a.m., with a maximum magnitude of 2.7 on the Richter scale.

The assistant to the city in charge of the ecological transformation of the territory quickly understood the origin of these tremors: deep geothermal energy.

Since 2010 and the commission of studies on the subject, the Eurometropolis has embarked on the exploitation of this renewable energy.

It is an integral part of his “2050 carbon neutrality plan”, voted under the former socialist majority, but with the support of environmentalists, now in power.

"Historically, we have resources in the soil"

"The objective of geothermal production is 620 gigawatt hours per year, which should represent a little less than 10% of the consumption of the community of municipalities in thirty years", summarizes Marc Hoffsess, before giving another figure .

“Thanks to that, we could ensure 40% of the heating needs of the agglomeration.

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There is therefore no question of giving up this practice, which consists of drilling about 5,000 deep in order to take advantage of the hot water flows that circulate through the existing faults.

“With the depression of the Alsace plain, we have historically had resources in the soil, such as oil for example.

Geothermal energy is one of them and is not new in the area ”, insists the deputy, aware nevertheless that the hard knocks are increasing.

Especially on the Reichstett-Vendenheim site, about ten kilometers north of Strasbourg.

Our geothermal file

On November 12, 2019, an earthquake with a magnitude of 3.3 on the Richter scale had already shaken Strasbourg.

As a precautionary principle, the suspension of drilling was ordered everywhere, that is to say also on the sites of Illkirch and Eckbolsheim.

Until a resumption of experiments, not of industrial activity, almost a year later, ie since October 1.

The operator Fonroche quickly recognized Thursday that the earthquakes felt were linked to its activity.

Before the Bas-Rhin prefecture confirms.

"We can admit microseismicity"

"Stopping the injection of water into well n ° 2 is a phase conducive to the generation of seismic phenomena because it induces pressure variations and rebalancing of internal stresses in the geological compartment", she writes in a press release, before specifying that "the continuation of the tracing test is suspended".

From now on, a committee of experts should look into the subject again.

For a new recovery in the coming months?

Marc Hoffsess hopes so, but under certain conditions.

“We will be very attentive to reducing technological risks.

We can admit microseismicity, it is normal, but it should not be impacting for the inhabitants.

We also want the most total transparency on the file.

Local residents' associations but also naturalists will be involved in the decisions taken.

We need the confidence of the people.

“So that they vibrate, too, for geothermal energy.

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