Results of Geomagnetic Routine Observations and Earthquakes(Ⅳ) Local Time Changes （ΔZ/ΔX）'s of pc 3-4 and pi 2 at Kanoya
Yoshimatsu, T.
Abstract
In this paper(ΔZ/ΔX)'s of pc3-4 and pi2 at Kanoya are examined in their characteristics in respect to the period T and (ΔY/ΔX), based on the rapid run records for the period from 1960 to 1962. The time derivatives X, Y, and Z of the pulsations and other rapid changes have been observed at Kanoya by air-core induction magnetometers since the IGY.(1) The double maximum amplitudes of the largest oscillation, ΔX, ΔY, and ΔZ are scaled out for pi2 with the quality A or B, and pc3-4 further including rather regular fine waves with quality C and with phase differences, Y-X =π土δYX, Y-Z =土δYX, δYX and δYZ≦π/5. The total number of material of pc3-4 and pi2 used for the investigation are 713 and 473, respectively.
The relation between ΔZ/ΔX and T is shown for the means of successive five-second interval of T in Fig.1, showing a fairly well correlated linear relation for pi2, but not so for pc3-4. The dependency of ΔZ/ΔX on ΔY/ΔX is expressed in Fig.2, in which pc3-4 shows a linear relation while pi2 does not so.
In the previous paper(2) the time changes of the monthly values, (ΔZ/ΔX)'s, of socalled short period changes with period of several minutes to several tens minutes were examined to show an intimate correlation with the activity of major earthquakes near the station. Then it is very interesting to obtain here the similar results in wide range of T of geomagnetic rapid changes. (Fig.3-5) In Fig.3 (pi2)m and (pc3-4)m are shown by the normalized mean monthly values of (ΔZ/ΔX)'s at T=54sec. and ΔY/ΔX=0.8, respectively, using the linear relations mentioned above.
It should be noted, however, that most major earthquakes occurred in the very months of the minimum values of (pi2)m and (pc3-4)m, while those of (ΔZ/ΔH)'s preceded one or two months the major earthquakes as shown atop in Fig.3. Considering this fact and that the minimum values of (ΔZ/ΔH)'s are recovered to the normal values of (ΔZ/ΔH)'s in the very months of major earthquakes, it may be suggested that some agency responsible for the occurrence of a major earthquake may be originated somewhere below the hypocenter in the deeper part of the earth three or four months before the earthquake, where the major part of the electric current corresponding to the so-called short period change flows, and may occur gradually an anomalous change of the distribution of the electric conductivity there, becoming largest one or two months before the earthquake. On the contrary, the change of the conductivity in the shallower part of the earth begins to occur about one month before the earthquake and attains the maximum in the very month of the earthquake as if the energy of the agency were propagated into the shallower part where the major part of the electric current responsible for pc3-4 or pi2 flows.
More data in longer period and more precise analysis at other stations are very desired hereafter.
