Results of Geomagnetic Routine Observations and Earthquakes(I)
Using the monthly mean values of the horizontal (H) and vertical (Z) intensities and their deviations, ΔH and ΔZ, from the twelve-month running averages, which have been observed at Kakioka, Memambetsu, and Kanoya magnetic observatories during a few recent years, the author intended to trace some geomagnetic changes, if any, due to the principal shallow near-earthquake of which magnitude is M ≧6.0 and epicentral distance from the observatory is less than about 300 Km.
Some statistical investigations by a Chree's superposed method show that monthly inequalities of ΔH's and ΔZ's between the observatories may attain their extreme values two or three months before the very month of near and larger earthquakes (Fig. 8 and 9).
It is strongly felt to the author through the present investigation that the establishment of dense nets of geomagnetic observations, each station being apart about fifty Km or less, in some frequent-occurrence regions of earthquakes as well as in the most infrequent-occurrence regions for reference could contribute more effectively to the fundamental physical investigation of the mechanism of the earthquake occurrence from the field of geomagnetism.