Geothermal drilling leads to minor quake

A geothermal drilling station near St. Gallen is being used to find hot water that could supply half the city's buildings with energy Keystone

Drilling for geothermal power sources caused a minor earthquake early Saturday morning, which was felt across a large area of eastern Switzerland from St. Gallen to Appenzell. The project has been halted while the quake is investigated.

The epicentre of the magnitude 3.6 quake was registered at a depth of four kilometres. The shaking is directly related to test measurements and simulations for the drilling of geothermal power plant project in St. Gallen, according to the Swiss Seismological Service (SED), based at Zurich’s Federal Institute of Technology. The project, which was put on hold following the quake, is the largest of its kind currently underway in Switzerland.

Minor damage to buildings as a result of such a quake can’t be ruled out, the SED noted, although none has been reported.

The goal of the geothermal drilling project is to find hot water (140 degrees Celsius) at about 4500 metres deep that will supply half of St. Gallen’s buildings with energy. The seismological service installed 10 measuring stations around the drilling area to monitor seismic activity, which they expected to be weak but consistently present.

Numerous small earthquakes were already produced over the past few days because of the drilling, and their intensity increased overnight Friday. The drilling has been halted while the quake is investigated and the hole has been closed. A crisis team is set to decide in coming days whether the project will continue.

An engineer working on the project told the Swiss news agency SDA that the drilling team encountered high-pressure gas while preparing to drill at a depth of more than 4,000 metres. They then flushed the gas out of the hole with large volumes of water and drilling mud, which may have contributed to the quake.

In Basel, drilling was stopped in 2006 in a similar project because of the risk of seismic activity. The project was eventually called off in December 2009 following a series of earthquakes, the largest of which registered 3.4 degrees on the Richter scale.