Abstract: This paper dealt with the anomalous changes in geo-electricity (apparent resistivity) at Chengdu station (Δ=35 km), a two-year descending tendency of 7.2% in NE direction associated with the Wenchuan M_S8.0 earthquake. We used an 1D model of negative resistivity changes occurring in the lower part of the bottom layer, so that a new interface appearing in certain level of the bottom layer. In the model, the negative resistivity changes are supposed to be due to the influences from the preparation processes of the quake, and also the consequence of the interface upward with the different magnitudes of the resistivity changes has been considered for comparison. The results show the appearances of the new interface with the negative resistivity changes would lead the geo-resistivity descending in a monotone behavior in the ground observation configuration system, with the increase of the magnitude of the resistivity descending and the interface level upward in the part of the bottom layer. For example, for the negative resistivity change being 20%, the interface level has to be up to the 122 m below the surface. As for other changes, for example, 15%, the level would be up to the 86 m shallower than 122 m, while for 30% the level could be 175 m, deeper than 122 m.

Key words: Geo-resistivity, Apparent resistivity simulation, The 2008 Wenchuan M_S8.0 earthquake, Chengdu station