The offshore magnetic data were analyzed to determine the depth of magnetic basement of Kyungi-bay. The mean depth to the basement was computed by a power spectral analysis method. To determine the relief of magnetic basement, the total magnetic intensity data were first reduced to the pole and transformed to a pseudo-gravimetric anomaly data using the Poisson's relation. The relief of basement was estimated from the downward continued pseudo-gravimetric anomaly data to the mean depth. In the process of data preparation, Tuckey and Harming filter was used to suppress the near surface effect of short wavelength. A band-pass filter was also applied before downward continuation. From the result of this study, it is appeared that the magnetic basement rock is ccmposed of mainly granite gneiss and depth to the basement rock is varied from 300m to 500m. The relief of magnetic basement is appeared to reflect the general topography in this area.

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