Image credit: Jérôme Dorkel – Eurométropole de Strasbourg

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A series of minor human-induced earthquakes in the area of Strasbourg, eastern France, last December has reminded local inhabitants about the safety of geothermal energy, highlighting the challenges faced by deep drilling technology, says Euractiv.

In December, the area around Strasbourg was shaken by several induced tremors, including one of 3.5 magnitude, after a geothermal company carrying out tests injected high-pressure water into the ground earlier in the autumn.

Induced earthquakes – those caused by human activity – had begun since tests started in the Alsace region in October at the geothermal plant operated by Fonroche, a French energy company.

The tremors were directly linked to the starting-up activities of the plant, said the French association of geothermal professionals, the AFPG.

“It appears that seismicity related to deep geothermal in Rhine Basin geologic reservoir is mainly associated with testing phases during drilling and starting-up operations,” AFPG said in a statement. “This seismicity is measured and monitored all along the construction and operating phases during which events are generally not felt,” it added.

Fonroche, the company operating the plant, confirmed to AFP that the shock was linked to its activities. In a statement, it said the December episode “could be a continuation of the movements induced by the tests undertaken” in October but was “also taking place in a context of intense seismic activity on the West European ridge for several weeks”.

The Alsace region is prone to natural tremors and has put in place a seismic plan to better map the risks and inform the population.

Several geothermal plants are already operating there, without causing major seismic activity to date. Tests on geothermal plants that use a technology called enhanced geothermal systems (EGS), can cause tremors, but those are controlled and usually don’t go above a level of 2 on the Richter scale.

For the geothermal industry, the tremors in December, which hit a level of 3.5 on the Richter scale, were “exceptional”.

“We see this as an excuse for people to say no to geothermal,” said Sanjeev Kumar, head of policy at the European Geothermal Energy Council (EGEC), an industry body. “For decades, we’ve been going ahead of the curve in terms of how we manage this,” he told EURACTIV.

After the December tremor, the French authorities requested the operator to close the plant. This started a progressive and total shutdown of the geothermal fluid circulation between the 5km-deep boreholes, which caused another 2.8 magnitude earthquake on 10 April.

According to Fonroche, those will stop once the plant is fully operational because the water pressure will be constant.

An investigation is ongoing into how and why the tremors were caused.

Full article here.

Strasbourg and the Alsace region saw a series of induced earthquakes – those caused by human activity – since October 2020 [Leonid Andronov / Shutterstock]

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April 13, 2021 at 09:18AM