地層中の応力場の解析法とその実例について

抄録

Using the minor-faults, M.V. GZOVSKII (1954) first proposed an analytical method for determining the stress-field caused by the tectonic movement. In the present paper his method is introduced, and its applied examples, which the writers actually verified at the sedimentary strata developed in the Miura Peninsula, are reported. At Sajima, the stress-field restored from the conjugate minor-faults well coincides with theoretical or experimetal one found on the anticlinal crest of plastically deformed strata. At the cape Choja-ga-saki, two sets of conjugate minor-fault groups, the older reverse-fault set and the younger normal-fault set, are recognized. The stress distribution obtained from the younger set (PL-I-2) is snch that the axes of maximum principal stress σ1 (where tension is treated as plus) have always a constant direction (E-W, near horizotal) and σ2 and σ3 axes, on the contrary, take rather random orientation on the planes perpendicular to σ1 axes. From the fact the writers concluded that the younger faults were generated by a tensile stress caused by a general upheaval of this area. From the writers' observations followings are emphasized: 1) it is important to distinguish each set of fractures at each locality. 2) it is much useful to find the axes of princi pal stress from one or a few pairs of fractures at many points, rather than to find those from the mean value of numerous fractures at a few points.