The determination of in situ stresses along deep vertical profiles was declared a key issue for two scientific deep drilling projects:
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the German Continental Deep Drilling Project (KTB) situated in northeast Bavaria in an area of complex variscian thrust tectonics and
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the CAJON PASS Project, located only about 4 km from the San Andreas Fault Zone In southern California.
In the KTB project 7 successful hydrofrac stress measurements could be completed in a 4 km deep pilot hole between 0.8 to 3.0 km. At the Cajon Pass site a series of 23 hydrofrac stress measurements was performed in 2 wells between 0.9 to 3.5 km.