球面調和解析에 依한 韓半島內의 地球磁氣場의 分布에 關한 硏究

Geomagnetic field distribution in the Korean Peninsula by spherical harmonic analysis

The position of any point on the earth’s surface can be represented in the spherical coordinates by surface spherical harmonics. Since geomagnetic field is a function of position on the earth, it can be also expressed by spherical harmonic analysis as spherical harmonics of trigonometric series of am(θ) cos mφ and bm(θ) sin mφ. Coefficients of surface spherical harmonics, am(θ) and bm(θ), can be drawn from the components of the geomagnetic field, declination and inclination, and vice versa. In this paper, components of geomagnetic field, declination and inclination in the Korean peninsula are obtained by spherical harmonic analysis using the Gauss coefficients calculated from the world-wide magnetic charts of 1960. These components correspond to the values of normal geomagnetic field having no disturbances of subsurface mass, structure, and so on. The vertical and total components offer the zero level for the interpretation of geomagnetic data obtained by magnetic measurement in the Korean peninsula. Using this zero level, magnetic anomaly map is obtained from the data of airborne magnetic prospecting carried out during 1958 to 1960. The conclusions of this study are as follows; (1) The intensity of horizontal component of normal geomagnetic field in Korean peninsula ranges from 2×10⁴ gammas to 2.45×10⁴ gammas. It decreases about 500 gammas with the increment of 1° in latitude. Along the same latitude, it increases 250 gammas with the increment of 1° in longitude. (2) Intensity of vertical component ranges from 3.85×10⁴ gammas to 4.75×10⁴ gammas. It increases about 1000 gammas with the increment of 1° in latitude. Along the same latitude, it decreases 150~240 gammas with the increment of 1° in longitude. Decreasing rate is considerably larger in higher latitude than in lower latitude. (3) Total intensity ranges from 4.55×10⁴ gammas to 5.15×10⁴ gammas. It increases 600~700gammas with the increament of 1° in latitude. Along the same latitude, it decreases 10~90 gammas with the increment of 1° in longitude. Decreasing rate is considerably larger in higher latitude as the case of vertical component. (4) The declination ranges from -3.8° to -11.5°. It increases 0.6° with the increment of 1° in latitude. Along the same latutude, it increases 0.6° with the increment of 1° in longitude. Unlike the cases of vertical and total component, the rate of change is considerably larger in lower latitude than in higher latitude. (5) The inclination ranges from 57.8° to 66.8°. It increases about 1° with the increment of 1° in lattitude Along the same latitude, it dereases 0.4° with the increment of 1° in longitude. (6) The Boundaries of 5 anomaly zones classified on the basis of the trend and shape of anomaly curves correspond to the geologic boundaries. (7) The trend of anomaly curves in each anomaly zone is closely related to the geologic structure developed in the corresponding zone. That is, it relates to the fault in the 3rd zone, the intrusion of granite in the 1st and 5th zones, and mountains in the 2nd and 4th zones.