The strain energy accumulating-releasing period and strong earthquake prediction in Sichuan-Yunnan rhombic block

In this paper, the Sichuan-Yunnan rhombic block is divided into two parts. The strain rate is achieved by deformation, the elastic modulus is acquired by velocity structure in the deep, the volume of the block is calculated by the area and thickness of block, and then the variation of accumulated strain energy with time is confirmed. On this basis, combined with the research of historical strong earthquakes, the relationship between the period of energy accumulating-releasing and the seismic activity is obtained. The results show that the strain energy accumulating-releasing emerges periodically, which can be used for strong earthquake prediction. The strong earthquakes (M≥7.0) do not occur at initial stage of strain energy accumulation. The strain energy increases continuously with time and then several strong events occur firstly, but each event is smaller in magnitude than the predicted ones, i.e., one event releases a small part energy and later energy increases incessantly. The energy is not completely released until one or two great strong events (M≥7.5) occur. Thus, the old cycle ends and a new cycle starts. Obviously, the quiet to active periods are caused by the cycle of strain energy accumulation from small to great, and then to completely releasing. Active stage is much longer than the quiet one. Therefore, it is unsuitable to discuss the quiet-active period for a great geographic area covered by many blocks or to discuss the repeat period of single strong earthquake for a small region. Although the occurrence of strong earthquakes does not obey any law in time, the magnitude predicted by the strain energy accumulating-releasing curves is coincident with the real one, which may be significant for seismic safety evaluation.