1-D crustal resistivity structure revealed by sea effect corrected magnetotelluric (MT) data obtained at Jeju Island, Korea

Jeju Island, a volcanic island in South Korea, has been one of the main targets of geophysical and/or geological studies because of its tectonic importance associated with the volcanism and tectonic link to the southern Korean Peninsula. In this study, we reinterpret deep structures of Jeju Island based on the 1-D inversion results for the sea effect corrected MT data. Among 108 MT sites, we select 11 MT sites, which are uniformly spread out across the island and have good quality data for frequencies ranging from 103 to 10− 3 Hz to examine the 1-D deep structures. The sea effect correction makes remarkable changes in the observed MT data at frequencies below about 1 Hz, playing an important role in revealing the deep structure. The 1-D resistivity models obtained from sea effect corrected MT data are greatly similar to one another, commonly showing the discontinuity at a depth of 18 km on average. This discontinuity can be interpreted as the transition zone separating resistive upper crust and conductive lower crust. This interpretation is consistent with the geophysical interpretations made for the southern part of the Peninsula which seems to be tectonically linked to Jeju Island. Reversely, this agreement can be the evidence supporting that Jeju Island is the extension of the Korean Peninsula.Considering the tectonic environment and formation process of Jeju Island, it is noted that the low resistivity of the continental lower crust (CLC) beneath the island can be explained by the interconnected saline fluids which are associated with metamorphic and/or magmatic activity forming the island. All the results convince us that the newly built 1-D model for Jeju Island matches other geophysical and geological evidences.

► This study reveals the the deep sbusurface structures of Jeju Island in Korea.
► Our results show the electrical discontiuity at a depth of 18 km on average.
► This discontinuity can be interpreted as Conrad Interface.
► Our 1-D model for jeju matches other geophysical and geological evidences.