Abstract: The G-R relation between the earthquake magnitude and frequency has been an important premise in seismological study, but its actual distribution often deviates from its theoretic result. Based on the experimental results of the three types of rock samples containing macro-asperity, compressional en-echelon fracture and model-Ⅲ shear fracture, this paper has newly fitted the G-R relation in the sequences of the rock sample's acoustic emission by the different scales of magnitude and frequency, and emphatically reviewed the change of the linear fitting coefficient value , which figures the actual deviation degree of earthquake magnitude and frequency from the G-R relation within every time window. The results show that the value that counted separately is becomes lower before the instability occurred in the process of deformation of the three types of rock samples, indicating that the deviation degree of earthquake magnitude and frequency from the G-R relation is increases. Some earthquakes cases tell us that the deviation degree exactly exists before the occurrence of moderate earthquakes. The results provide certain useful reference in searching the precursors before the occurrence of moderately strong earthquakes by using the data of the regional seismic activity.

Key words: Rock fracture experiment, The G-R relation, Deviation, Earthquake prediction