異方性岩石における選択的破壊について

抄録

For the purpose of investigating the fracture process of earthquake which will be affected by various kind of anisotropy in the earth's crust, we carried out triaxial test up to 500MPa (5 kbar) of confining pressure for the suitable anisotropic rocks for the present study, that is, gneiss and graywacke sandstone.
For gneiss with the anisotropy oriented at 45° to the principal stress axis, the strength was widely distributed and the small rapid stress drop occured frequently below 240MPa of confining pressure. Above 240MPa, on the other hand, the strengh was fitted well with a single curve, which was lower than that for gneiss with the anisotropy oriented at 90° to the pricipal stress axis, and the large stress drop occured.
These results means that at low confining pressures (less than 240MPa) the effect of anisotropy on the fracture is small and local, but at higher confining pressure (more than 240MPa), this effect spreads all over the sample.
It is interesting for earthquake prediction to study the complex strain variation and the phenomena of multiple stress drop, because they result from the fault formed in the inhomogeous distribution of strengh obtained for the moderate anisotropic rocks. It seems important for speculating micro-earthquake distribution for depth that the behaviour of stress drop and strength for gneiss are stongly affected by confining pressure.