Geopower Basel was drilling to reach hot rocks some five kilometres under ground that would power an enhanced geothermal system (EGS), in which water is injected down a well, heated and returned to the surface where it powers a turbine generator. The effort is blamed for earthquakes, including a 3.4 magnitude temblor in 2006, and last week a review by city authorities determined the risk was too high for the project to continue drilling.