The German Continental Deep Drilling Program (KTB) has been a remarkable attempt to learn more about one of the least understood parts of the outer Earth — its crystalline continental crust. But reports from the project have not circulated widely, hence the value of a special set of papers in Journal of Geophysical Research (102, No. B8; 1997) which is intended to bring the main scientific work of the KTB project to a wider audience.
In drilling through the top third of the crust, the project has provided a laboratory to relate deep-rock properties to those inferred from surface measurement, and has also shown that the best predictions of what rocks would be encountered at depths of just a few kilometres were woefully inadequate. Drilling lasted from September 1987 to October 1994, during which time a 4-km pilot hole was drilled and cored, followed by a 9.1-km main hole. Extensive downhole logging and continuing experimentation has produced a vast amount of data.
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