This paper presents lateral conductivity variations in the Earth's crust in and around the southern Korean Peninsula, which were mapped using magnetic field variations recorded at ten sites in Korea. GDS data can provide an efficient way to identify crustal units having different conductivities. And a three-dimensional (3-D) magnetotelluric (MT) modeling based on the induction arrows revealed a major conductivity anomaly in and around the Korean Peninsula. The comparison of observed and modeled induction arrows strongly suggests evidence of a relationship between main tectonic belts and the deep conductivity anomalies in this area. The overall pattern of induction arrows in this area appears to indicate a northwest-southeast direction, which is similar to that of the so-called 'sea effect', affected by the surrounding sea. However, the results of observations in the middle of the peninsula imply an anomalous pattern in the tectonic area near the Imjin River Belt. Induction arrows in the mid-southern area appear to be related to a thick sedimentary pile, the Ogcheon Belt, which forms another tectonic boundary in the Korean Peninsula. The overall pattern of arrows observed in the coastal area and islands was affected by the sea effect. The pattern, which shows southward arrows similar to those in the previous study of the southern coastline of the peninsula and Jeju Island near Kyushu, Japan, might indicate highly conductive anomalies (HCL) (Shimoizumi et al., 1997). However, the sea effect seems to be weak in the western coastal region, probably because the Yellow Sea is much shallower than the East Sea (Sea of Japan), and this phenomenon leads to the possibility of discerning an anomalous pattern beneath the Yellow Sea.
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