Oh, what a surprise!
Geothermal drilling in Bale, Switzerland, in 2007 caused several earthquakes, leading to some 2.700 insurance claims at a total cost of around 7 million USD.
Another geothermal project in nearby Staufen resulted in prolonged ground elevation of up to 1 cm/month, causing severe damage to its historic old town (
video-unfortunately in German, but the pictures speak for themselves)
But that hasn't to do anything with fracking! Well, it has, among others, to do with injecting water into
Anhydrite (CaSO4), which leads that mineral to transform into gypsum (CaSO4·2H2O), thereby gaining volume. Anhydrite is a sediment, formed by evaporation of shallow saline waters. Now, guess how oil and gas deposits have been formed - right, by sedimentation of organic material, especially algae and plankton, at the bottom of saline waters. Pressure and heat transform these deposits into oil and gas, which then migrate upwards through the covering sediments until they become trapped beneath an impermeable rock layer, the so-called seal rock. While there are several types of seal rocks, the most common one is a
salt dome, created by evaporation of shallow saline waters and including - yes - anhydrite.
In other words - injecting water into anhydrite, which leads to volume gains and earth movement, is an inherent risk of fracking. Now, there may be oil-bearing geological formations that hardly contain anhydrite (and Western Texas, around Midland and Odessa, appears to be such a formation), but those are rather the exception than the rule.
