封圧下における異方性岩石のAEの発生様式

抄録

The acoustic emission that occurs during tri-axial compression test of anisotropic rock samples stratified was studied under confining pressure up to 300MPa. The m value of Ishimoto-Iida's formula was determined by the comparator with the seven channels of different threshold levels. Occurrence pattern of acoustic emissions and variation of m value for Kamioka gneiss were strongly affected by the direction of layers of rock. On the specimen with layers of rock oriented at 45° to the principlal stess axis, many axial stress drop were observed, which is caused by the existence of weak zone of the anisotropic rocks stratified. The m value changed before and after these axial stress drops. Frequency-amplitude relation of gneiss was represented by two straight lines before axial stress drop, but represented by a single straight line after axial stress drop. The m value of Miyama sandstone had decreased untile axial stress drop, and recovered after axial stress drop. Associated with small axial stress drop caused by local fracture in sample, the activity of forshocks was weak and the vigorous aftershock activity decayed rapidly. When the large axial stress drop was produced by the frictional sliding after several local fractures, the foreshock activity became higher immediately before axial stress drop, and then the activity of aftershock decayed slowly. The consideration from investigetions of acoustic emission are summarized with respect to the various types of axial stress drop occurring in anisotropic rock samples stratified.