TEN EXAMPLES OF CHANGES IN EARTH-RESISTIVITY PRIOR TO STRONG EARTHQUAKES

Other then the 1976 Tangshan Earthquake, ten more examples of changes in earth-resistivity (ρ_x) prior to strong earthquakes, five of which with magnitudes M6, are given in this paper. There are always at least two earth-resistivity recording stations located around the epicentral area of each of the earthquakes, recording the changes of ρ_x values, quite in accord with each other. For a part of the earthquakes are given also data of repeated base line surveys, in the vicinity of some of the earth-resistivity stations for comparison.For many cases, the earth-resistivity values of the shallow layers below the ground surface decrease prior to the earthquakes, just as in the case of the Tangshan earthquake. However, in, a number of cases, they increase or vary irregularly. The purpose of this paper is merely to provide an accumulation of more such observed phenomena of earth-resistivity changes around epicentral areas before and after strong earthquakes. It is because that earth-resistivity changes observed at stations before and in the vicinity of strong earthquakes are rare opportunity so far as such observations carried out in earthquake regions of the whole world are concerned, despite such observed changes in earth-resistivity is restricted to very shallow layers of the ground.