For studying the relation between earthquake faulting and a pre-existing plane of weakness, the amphibolite samples were given special treatment. In the first group, the rock samples were sawed into two with the angles of 20°, 30°, 40°, 50°, between sawing plane and axial direction of the sample and then the two parts of the sample were adhered to each oth er with the epoxy resin. In the second and the third groups, the rock samples were sawed into tmo thirds and one third of the diameter of the samples respectively with the sample angles mentioned above, then were filled with the epoxy resin. The epoxy resin filled in the samples formed an artificial plane of weakness. The samples described above and the intact rock samples were tested under the confining pressures of 0.79k bars and 3.03k bars with constant strain rate of 10^-5 per second. It was found:
1. The process of fracture in the partly cutting samples consists of two major subfractures which followed one another closely. The first one is the fracture of the plane of weakness, the second one is a new fracture in rock;
2. The fracture in the samples which were cut through is along the plane of weakness completely. The fracture in most of the samples which wene cut into two thirds of its diameter developed along the plane of weakness but the fracture in the samples with cutting angles of 20° and 50° under confining pressnre of 3.03k bars is in the conjugate direction of the plane of weakness. All of the fractures in the samples which were cut into one third of its diameter pass through the end of cutting and most of them are in the conjugate direction of the plane of weakness, but the included angle, smaller.
3. The plane of weakness had obvious effect on the strength of the samples. The deeper the cutting, the lower the strength. The cutting angle also influences the strength of the samples which were sawed into two or into two thirds of its diameter, but there is no effect of the cutting angle on the strength of samples which were sawed into one third of its diameter.
By means of the results from the experiment, the relation was discussed between the earthquake faulting and the plane of weakness.