In Southeast China, strong shocks(M≥4(3)/(4)) often present dual activities along a fault zone.Along with the symmetric feature of rhombic and monoclinal types in geological structure, it reflects the symmetric feature of tectonic stress and crust movement. Because of the difference of some factors which affects the process of earthquake occurring, the difference between magnitudes of the two earthquakes in pairs reaches 0-1 M, the interval is from several months to near hundred years, and the distance of epicenters is 15-300km. These parameters are closely related to the regional concrete conditions.
The strong shocks occurred in pairs make up 61 per cent of the total strong shocks in this region, during 1500-1977, it indicates that it has rather an universal feature that the earthquakes often occur in pairs. Therefore, the discovery is useful for earthquake prediction.