During the hydrofracturing experiments at Mitsui-Ashibetsu coal mine, observations of Acoustic Emission (AE) were carried out inorder to study the fracture mechanism. Six piezoelectric accelerometers were used for the observation. Hypocenters of 632 AE events were located during the experiment.
The results of the observation revealed the following characteristics of the AE, (1) the spatial distribution of hypocenters of AE is a fractal, and the fractal dimension is 2.08, (2) the plane of AE hypocenters' distribution is approximately perpendicular to the direction of the minimum principal stress in rock of the experimental site, and (3) the frequency content of the AE located in coal is lower than that of the AE located in rock.
And, we could revealed the process of hydrofractures' formation from the change of AE events rate and AE hypocenters' distributions.
Subsequently, analyzing the change of AE event rate and hypocenters' distributions, the process of hydrofractures' formation was discussed.
