Monday, December 21, 2009

Geothermal Energy And Earthquakes

Theunis Bates at Sphere has a good write up about the link between geothermal energy projects and earthquakes.

These projects are controversial. The company that started a geothermal project in Basel, Switzerland is facing lawsuits for allegedly triggering earthquakes. Another project in California was recently canceled due to similar earthquake fears.

From the article:

Paul Younger, a professor of energy and environment at Britain's Newcastle University, says that it's not unusual for much smaller tremors to be felt on the surface when pressurized water is forced into rock deep underground. But, he adds, the process is normally only carried out in seismically stable areas, as the shakes caused by hydro-fracturing can interact with existing deep faults and cause larger trembles.

And Basel is anything but stable. The city has a long history of quakes and was all but wiped out in 1356 by an estimated magnitude 6.5 earthquake – the largest ever known to have occurred in Western Europe. "What they were doing was actually fairly conventional," Younger says. "It's where they were doing it that was unconventional. If you go drilling and stimulating near a known active fault, you're asking for trouble."

That may raise a question. Why not just drill in portions of the crust that are known to be structurally very stable and which have no active faults?

....geothermal projects will almost always be located in geologically active areas with lots of faults and which are earthquake prone because the required heat will be found at shallower depths making such locations economically more attractive than drilling deeper in colder more stable parts of the crust.

As our understanding of faults in geologically active regions increase it may be possible in the future to more carefully select sites based on how "stressed out" individual faults are....but there will always be a general overlap between geothermal sites and earthquake prone areas.

Here is the situation for India. Earthquake potential (increases in darker shaded areas) compared with geothermal potential. There is large overlap as expected.

According to a report by D. Chandrasekharam of the Indian Institute of Technology Mumbai, the geothermal provinces of India have a potential to produce around 10,600 MW of power. I haven't seen other government figures for this.  The Ministry of New and Renewable Energy website does not have the numbers for geothermal. 

In any case, if this industry is to have a future, geologists and engineers will have to grapple with the connection between attractive geothermal energy sites and potential earthquake hazards and also importantly develop strong transparent public outreach mechanisms to disseminate information for review and debate.