A micro-fracture with a magnitude of about -2 occurred at a depth of about 700m in the Nakatatsu mine after about 48 hours from the latest explosion for excavation. The location of the micro-fracture was obtained at a distance of about 15m from the newly excavated face. The micro-fracture was accompanied with many aftershocks. The linear dimension of the aftershock area was obtained to be about 1m. The number of aftershock per unit time decreased hyperbolically with the time elasped after the main shock, similar to those of large, moderate and small earthquakes. The p-value in the modified Omori's formula was obtained to be 0.84. The m-value in the Ishimoto-Iida's formula for the aftershocks was obtained to be 2.01. These statistical properties of the aftershocks of the micro-fracture are the same as those of earthquakes. In a rock test, large AE events are also accompanied with aftershocks. The number of the aftershocks of large AE events decreases hyperbolically with time, similar to those of earthquakes. It may be concluded that the fracture in rock is accompanied with aftershocks and that the number of aftershocks decreases hyperbolically with time out of relation to its rupture size.
