Distribution of the Earth's magnetic field in Akita prefecture Part 1
Yumura, T.
Abstract
From June to October, 1940, the magnetic observation of the vertical and horizontal intensity was carried out in Akita prefecture by the author and Mr. S. Kikuti.
The number of the stations for observation was 384, in which three standard stations, Akita, Odate and Yokote were included, and the instruments used were the vertical and horizontal field-balance by Ad. Schmidt.
The object of this survey were not only to obtain the distribution of the Earth's magnetism in Akita prefecture, but also to investigate the following:
(1) the distribution of the magnetic intensity over the oil-field,
(2) the character of the magnetic field due to a volcanic mountain.
Oil-exploration is an indirect application of the magnetic method and furthermore has a double indirect nature. First, oil itself can't be found magnetically; we must rely on finding favourable structures in such formations as are expected to be oil-bearing; secondly, inasmuch as these formations are mostly non-magnetic, we must attempt to find igneous rocks which bear a known structural relation to the potential oil-formation,-the anticlinal formations of buried igneous rocks and the faults of the same rock or of crystalline formations.
As above mentioned, it is very difficult to apply the magnetic method to the oil-exploration but the writer almost accomplished his object by observing the anomalous band parallel to the oil-field which runs from south to north nearly along the coast of the Nippon Sea and by the detailed observation about the Asahigawa oil-field lying in the northern part of the field. (The latter result will be mentioned in Part II of this manuscript.)
For the second object, by the observations of two volcanic lakes, Towada and Tazawa, the author found some typical anomaly as a magnetic property of volcanic mountains.
The distribution of magnetic forces about volcanic mountains was observed at Mt. Fuji by Professor A. Tanakadate and Mt. Mihara by Dr. T. Nagata, etc., and these results agree with that of the author about the surroundings of the central part of the mountain, but, since their observing stations were chosen roughly, those results could not give the state near the centre.
As the writer chose the denser net of stations near the centre, the state of the central part was considerably brought to light.
The direction of the magnetisation of subterranean rocks at Towada was found by the method, originally given by the author. (See the preceding paper, “Some problems of the relation between magnetic disturbed force and a magnetized body.")
