Monofractality of Two Dimensional Natural Fracture Networks in the Kurihashi Granodiorite in the Kamaishi Mine, Northeast Japan

Abstract

Monofractality of the fracture networks in the Kurihashi granodiorite in the Kamaishi Mine was evaluated by using the box counting method. The fracture maps for fractal analysis were obtained by tracing fractures including open cracks, hydrothermal alteration veins and quartz veins at the scale mostly 2.0×4.0 m² on the wall rock of the E. L. 250 mL drift. The accuracy of the fractal dimension by the box counting was examined by taking account of the lower and upper cut off levels, so the fractal dimension could be higher quality enough to characterize the natural fracture networks. Distribution of fractures and alteration veins ranging from 1.5×1.5 m² to 2.0×2.0 m² were identified by monofractal, and their dimensions D were ranging from 1.04 to 1.09, however, the distribution of open cracks and quartz veins were non-fractal. The distribution of alteration veins in the E. L. 250 mL drift (2.5×360 m²) was also characte-rized. The long fracture map was divided into 12 units and piled up to compose virtual fracture maps at the scale 30×30 m². The distribution of alteration veins was characterized by monofractal and its dimension D ranges from 1.08 to 1.11. The distribution of alteration veins shows monofractality with similar dimensions (D from 1.04 to 1.11), which means that the distribution of alteration veins ranging from 1.5×1.5 m² to 2.5×360 m² could be characterized by an unique monofractal dimension.