Character of geoelectric intermediate term precursory anomaly and judgment for intermediate term tendency of strong earthquake

Based on systematic processing to long-term geoelectric observation data, we mainly studied the character of earthresistivity tendency anomaly for MS7.0 strong earthquakes and its relation with seismogenic process. The character of quick descending at early stage and then slow development with steady shape in geoelectricity is a basicfeature ofgeoelectric tendency anomaly for strong earthquake. Usually the ratio of average time between the earlyquick descend stage and the post slow development stage is about if4. In addition, for Tangshan Ms=7.8 andSongpan Ms=7.2 earthquake, we studied the diffusion character of the geoelectric tendency anomaly development.For Tangshan earthquake, we also studied the time-space-strength dynamic evolution character of its geoelectricprecursory information quantity. The results showed that diffusion velocity of geoelectric precursory tendencyanomaly for the two earthquakes is respectively 90 kmja and 100 km/a. The variation character of geoelectric tendency anomaly presents some indexes for judgment of strong earthquake tendency background and intermediateterm prediction.