Analysis of Sea Effects on Magnetotelluric data from the Yeonil Tectonic Line and Ulsan Fault, Korea

초록

Several hundred of micro-earthquakes have been observed near the Yeonil Tectonic Line and the Ulsan fault in South Korea after the Gyeongju Earthquake in September 2016. A magnetotelluric (MT) survey was conducted to identify the deep geology of the microseismic zones. The MT data are influenced by the high conductivity of the sea near the MT survey sites. In particular, the sea area can be misinterpreted as a distribution of false low resistivity anomalies if the sea effects are not considered. The study area is mostly mountainous and bounded by the sea to the east. Three-dimensional numerical modeling was performed to investigate the influence of the sea on the MT data in the study area. The MT response curves are similar to those of the homogeneous model at high frequencies. However, at low frequencies, the difference between the XY and YX mode resistivity curves becomes larger due to the electrical conductivity of the sea. Similar to the numerical modeling results, a distortion of the resistivity curves due to sea effects was observed in the field data. Finally, geological structures beneath fault and weak zones were delineated by deep electrical resistivity cross sections. © 30th European Meeting of Environmental and Engineering Geophysics, Held at the Near Surface Geoscience Conference and Exhibition 2024, NSG 2024.