抄録
After the accomplishment of the World Magnetic Survey (W. M. S.), the aeromagnetic survey of the total force has been carried out by the Geographical Survey Institute. The surveying regions are the south-western part of Japan: Kanto district in 1966, Kinki district in 1967, Chubu district in 1968, Shikoku district in 1969 and Kyushu district in 1970 (see Fig. 1). The height of measurement is generally about 3, 000 m and the instrument used is a proton precession magnetometer, whose accuracy is ±10 gammas. The transient magnetic variations and the perturbing magnetic field due to the craft are reduced. The continuous records of the total force at the Kanozan Geodetic Observatory (G. S. I.) are used for cancelling the transient magnetic variations. After two corrections the final accuracy of the total force is estimated as about ±20 gammas. The lines of equal total force and the isanomalic charts are shown in Figs. 3, 4 and 8. The isanomalic charts are derived by taking difference between the observed and the computed values (I. G. R. F.) in the height of 3, 000 m. Especially, the isanomalic charts are obtained on the plane 10 km high in order to clarify the regional pattern of the underground structure. The magnetic anomalies over Chubu, Kinki and Shikoku districts are negative. The magnetic low along the Median Tectonic Line seems to be related with the low sus-ceptibility of metamorphic rocks covered the earth's surface. The negative anomalies with large scale are found over the central Chubu district, the western Shikoku district, the south-western part of Iki island and the north-western part of Sakura-jima volcano. The positive anomalies with large scale exist over the northern, central and southern parts of Kyushu district. It seems unlikely that these anomalies are caused by volcanoes directly. The negative and positive anomalies with large scale may be related with the crust and mantle structures.
