Abstract: The simi-variogramanalysis is introduced to study the seismicrelativity in this paper. While applying this method to the typical seismicregions and sequences, the authors detect unexpectedly not only theperiodicity of earthquakes in North China, but also the distinct difference of relativity between foreshocks and after shocks of Songpan earthquake.

Key words: Structural analysis, Simi-variogram, temporal relativity, Strong earthquakes in North China