Apparently, artificial ‘enhanced’ geothermal sites may cause earthquakes. The concept (mentioned here before) is to drill shafts down into hot rock formations, pump in cold water, and generate steam to drive turbines. It would considerably increase the number of regions where geothermal power could be used.
According to Swiss government seismologists and officials on the Basel project, an artificial geothermal project caused an earthquake in Basel in 2006 and was subsequently shut down. Even after the shutdown, thousands of smaller earthquakes occurred in the following years. Now, there are concerns about a project that AltaRock Energy wants to undertake in California. Google’s philanthropic arm is investing $6.25 million in the project. The proposed site already experiences as many as a thousand small earthquakes per year. This video has some further details.
Obviously, the earthquake risk needs to be assessed and managed. It may be that not as many sites are suitable for enhanced geothermal as previously assumed. Perhaps such projects will only prove viable in sparsely populated regions. In any case, it is an unfortunate blow to an otherwise promising looking type of renewable generation.