Abstract: A new method has been proposed to analyse quantitative changes of earthquake activities based on relative intensity (RI) algorithm. Numeric tests indicate that this method can reflect some characteristics of seismic activities on space and strength. This method is applied to investigate earthquake activities in east China area since 1970. The results demonstrate that 4 moderate earthquake events all occurred at the uplift stage of similarity curves of the regional earthquake activities. 2~3 years before the moderate events, there are significant low values on similarity curves calculate on adjacent periods compared to those of 1970 reference.

Key words: Earthquake activities, Similarity curve, East China