FIELD: geophysical methods of examination of boreholes to expose zones o geological complications while drilling superdeep and deep holes. SUBSTANCE: natural electromagnetic field along axis of borehole is measured on several specified frequencies. Anomalous values are used to predict presence of jointing zone. Ratio of amplitudes of signals recorded on each frequency to signal recorded on lowest frequency is computed. Relative size of cracks is evaluated by computed ratio. EFFECT: enhanced authenticity of exposure of jointing zones and of determination of relative sizes of cracks. 1 dwg
