17. 櫻島に於ける地球磁氣觀測結果及び新熔岩の磁氣的性質
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概要
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On March 9, 1946. Volcanic island Sakurazima began its activity. The writers measured the anomalous magnetic field and its changes on the volcanic island, Sakurazima, during the period of March 23 to April 17. The chief results are as follows. (1) The local anomaly of geomagnetic declination, D, due to the magnetization of the Sakurazima is shown in Fig.2. Assuming that the specific intensity of magnetization J is equal to that of the natural residual magnetization Jn, we get the equation of the anomaly of the declination as, tg ΔD=-0.004sinΦ-0.026sin2Φ. In this equation, if we make some corrections of the observed values we can find that the observed values of D are well expressed in this equation. From this fact, it may be said that the direction of the magnetization agrees with that of the present meridian, and that a part of this magnetization of Sakurazima, for the most part, is due to the presence of the natural remanent magnetization in rock. (2) The result of the measuring of the magnetic properties of the newly ejected lava are shown in Table.I-2, I-3. The average value of specific susceptibility is about 0.98×10^<-3>, while that of natural residual magnetization is Jn～6.0×10^<-3> e.m.u., these values being fairly. smaller than those of basaltic rocks. (3) Although it has been reported that there was some remarkable magnetic. changes accompanying eruption of volcanoes, Asama and Mihara, we could find no changes in both of ΔD and ΔH in the case of presenteruption of Sakurazima. This fact may suggest us that there is some necessary conditions for anomalous changes in geomagnetic field accompanying volcanic eruption, such, for example, as the "magnetizibility" which is usually predominant in the basaltic rocks.
- 東京大学地震研究所,Earthquake Research Institute, University of Tokyo,地球物理學敎室の論文
- 1948-06-30