2D resistivity structure around the 2016 Gyeongju earthquake zone in Korea by MT survey

On September 12, 2016, M 5.8 earthquake, which is the largest magnitude ever recorded in the seismograph in Korea, occurred in the Gyeongju area. This earthquake was accompanied with foreshock (M 5.1) and thousands of aftershocks including M 4.5 event. Hypocenters of the earthquakes were located at the 12 ~ 15 km depth. The earthquake zone around epicenter of mainshock have been distributed around the Yangsan fault, Moryang fault, Ulsan fault including many unknown faults, and it was required to understand the deep depth structure to get the clarifying occurrence mechanism and its geological correlation with earthquake.

In this study, we carried out two-dimensional (2D) magnetotelluric (MT) interpretation to estimate the electrical structure around the earthquake zone. Audio frequency magnetotelluric (AMT) survey were measured at 301 stations and MT survey carried out at 153 stations. The observed data had artificial noise from human activity and electric facility like electric fence and electric train and the estimated artificial noise was exclude for MT signal improvement. The 2D resistivity distribution was estimated using MT2DInvMatlab(Lee et al., 2009) with active constraint balancing(ACB) algorithm. More geological information and 3D inversion will be required to improve the interpretation.