variegated seismological conditions has been accumulated. The method has been developed further in two main directions: - the perfection of the techniques and equipment of three-component field studies incorporating a continuous control of the identity of equipment both in deep boreholes and on the surface; - the creation of efficient and straightforward software for the automatic processing of PM data. Whereas the early stages of development of the method have been conspicuous chiefly by the use of polarization for the discrimination of the wave field, in recent years the emphasis shifts to...