Six Seismic Tremors Within 24 Hours Near Strasbourg, France Linked to Human Activity

Four separate small earthquakes shook the ground around Strasbourg, France, between Friday and Saturday, Le Monde newspaper reported Saturday. But data from the National Seismic Surveillance Network (RéNaSS) seemed to indicate that six validated seismic events had occurred between 11 p.m. local time on Friday and 3:30 p.m. local time Saturday—and that all had been "induced" by human activity.

The weekend's series of ground shakes—which the paper described as "very light"—occurred on the third weekend of Strasbourg's famous Christmas Market, a seasonal attraction that draws tourists from all over Europe and the world to the city, which has proclaimed itself the "Capital of Christmas." This year, as in the past, the city expects 2 million visitors to pass through its seasonal outdoor market, according to the Strasbourg Office of Tourism.

In reporting the recent spate of tremors, Le Monde noted that following a 3.9-magnitude quake that shook the region on November 12, "researchers and seismologists" had determined that it was "possible" the earthquake was caused by geothermal energy supplier Fonroche Géothermie. Local authorities subsequently shut down activities at the company's geothermal drilling sites until "the origin of the tremors that had shaken the Alsacian capital had been determined."

Geothermal energy is tricky because it offers a clean, renewable energy source on the one hand, but relies on the uncertain science of drilling deep into the the Earth's crust in order to access the heat trapped within bedrock.

Geothermal energy has long faced resistance based on fears that it may lead to stronger earthquakes. On December 8, 2006, a geothermal well in Basel, Switzerland, just over 70 miles south of Strasbourg, caused an earthquake, "shaking and damaging buildings and terrifying many in a city that, as every schoolchild here learns, had been devastated exactly 650 years before by a quake that sent two steeples of the Münster Cathedral tumbling into the Rhine," as The New York Times reported.

That same year, another man-made disaster caused by geothermal drilling occurred when a mud volcano erupted in Java, eventually displacing 30,000 residents as it continued to spew over two years.

As seismologist David Oppenheimer of the U.S. Geological Survey Earthquake Hazards Team told Scientific American in 2009, the trick to safely pursuing the benefits of geothermal energy is to "keep the size of the fractures small," though he also noted that geothermal energy is only available in "tectonically active areas," where the Earth contains naturally occurring faults that have trapped heat and gas over the millennia. Areas prone to earthquakes, such as California or the Alps, where Strasbourg and Basel are both located, are ideal for tapping geothermal reserves.

Fonroche "vigorously contested" allegations that the November quake was related to its geothermal drilling, arguing that the quake's epicenter was not near its working area, Le Monde reported.

Fonroche and RéNaSS did not immediately respond to requests for comment from Newsweek.

A picture taken on June 7, 2016 shows parts of France's first deep geothermal power plant which will collect water at 165 degrees in the center of the Earth to provide steam to a starch factory, during its inauguration in Rittershoffen, eastern France. - Made by the ES group (Electricity of Strasbourg), a subsidiary of French electricity giant EDF, the installation will produce 24MW which will provide heat to 27 000 housing. Local authorities expressed concern that recent earthquake near Strasbourg was due to geothermal drilling. Patrick Herzog/AFP