Abstract:

In this paper,the b-value of acoustic emission for the sample with "λ"-pattern cracks and the physical significance of the frequency-magnitude relation were experimentally and theoretically studied.The geometry of μλπ-pattern cracks influences the b-vnlue,and the b-value is very low.There are two kinds of processes of the b-value as a function of loading:one is that b decreases continuously and keeps low as loading level increases;the other is that b decreases and then rises or rises undulately.The change of b-value probably is closely related to the microfracturing processes.According to the physical picture of origination,propagation and coalescence of mierofractures,the distribution equation of microfractures was established.In the case without the interaction of cracks,the solution of the distribution equation is the Gutenberg and Richter relation.In the case of crack interaction,the solution of the distribution is not a simple power function,the frequency-magnitude relation deviates from linearity in logarithmic coordinates and it may be a precursor of large earthquakes.