Abnormal Variations of Earth Current Potentials Observed at Kakioka Just Before and After the 1944 Tonankai Earthquake
Yoshimatsu, T.
Abstract
It is very interesting to note that in Fig. 1(A) is seen a remarkable time variation of the mean curve of hourly values of D=E1.0-kE0.1, which begins to decrease about one day before the earthquake and manifests a broad minimum around the occurrence time of the earthquake indicated by the first thick arrow in the figure. E1.0 and E0.1 are earth current potential differences expressed in unit of mV/km which are observed by two independent E-W base lines of 1500 m and 100 m long， respectively. k is a constant determined statistically by short-period variations which occur simultaneously with geomagnetic ones. The range of this decrease of D curve amounts to about 11mV/km which is the largest value among some similar D variations hitherto reported by the author.
A similar variation of D can be also seen in Fig. 1(B) where an another 100 m line is considered. This shorter line was temporally installed shortly before the earthquake at the same place as the 100m line in Fig. 1(A), the electrodes buried being different in type and depth from the old shorter line.
After the earthquake the mean curve of D recovers gradually to a certain level less than the initial constant value observed during the period from 1 to 4, December. (Fig. 2)
Corrigenda is attached to this text.
