Studies on the Magnetic Local Attraction in the Region of the innermost recess of Kagoshima Bay, the Tokara and the Nansei Islands II

The magnetic local attraction and horizontal force in the coast of Tanegashima were investigated in November, 1982. The following results were obtained ; 1) The maximum value of local attraction is 0.94°W'ly and the mean absolute value is 0.33° in Tanegashima. These values are somewhat less than the values in Kagoshima Bay and its vicinity including volcanic stratums. Therefore it is considered that there is no effect of local attraction on a magnetic compass. 2) Measuring the horizontal force with the local attraction, the partial magnetic anomalies which have a large north-and-south component are observed, where there are little local attraction. 3) It is observed that large magnetic anomalies with irregular direction exist in areas of iron sand deposits. 4) In the northern region having hardly iron sand deposits, there is a magnetic anomaly, of about 500nT, which covers a wide area.1982年11月に種子島において地方磁気及び水平分力の陸上測定を行い,次のような結果を得た。1. 地方磁気の測定結果は,偏東の最大値が0.84°,偏西の最大値が0.94°,絶対値の平均が0.33°であった。これは火山性地質の多い薩摩・大隅地方の平均より小さい値だった。よって磁気コンパスへの実用上の影響は少ないと考えられる。2. 地方磁気と同時に水平分力を測定することにより,地方磁気が小さい所でも南北成分が大である局部的磁気異常が認められた。3. 砂鉄鉱床上には方向不定の比較的大きな磁気異常が存在した。4. 北部地域で砂鉄鉱床以外の要因によると考えられる,比較的広範囲の磁気異常が認められた