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The theory of faulting developed since E. M. Anderson’s (1951) work, which is based on the concept of dislocations in an elastic continuum, is systematically discussed. Recent work enables the problem to be properly formulated in three dimensions and leads to the confirmation of Mohr’s hypothesis, on which Anderson’s theory was based, that faulting is independent of the intermediate principal stress. Estimates of the stress-differences existing in the crust and mantle (ranging up to several hundred MPa––several kb) emphasize the significance of conditions which enable the high friction existing on deep faults to be circumvented so that faulting can take place under small stress-differences. The Hubbert-Rubey (1959) hypothesis of lithostatic pore fluid pressures remains the most attractive mechanism for overcoming the problem of high friction.
