To prevent serious problems occurring in abandoned mines such as ground subsidence, it is commonly carried out to fill cavities with some materials. During or after the cavity-filling process, we need to monitor distribution of filling materials in abandoned mines. Various geophysical methods, such as microgravity, electrical resistivity, ground penetrating radar, and seismic methods, have been used to describe abandoned mines themselves or to monitor distribution of filling materials. Microgravity, electrical resistivity, ground penetrating radar, and microseismic methods can be used to detect cavities, but may have some limitation in monitoring material distributions. In this study, we apply the seismic reflection method to image distribution of filling materials in near-surface abandoned mines. As the imaging methods, we use full waveform inversion and reverse time migration. In addition, we apply seismic interferometry to obtain better results. The full waveform inversion and reverse time migration methods are applied to four models which can mainly appear in abandoned mines. Through numerical examples, we investigate feasibility of seismic reflection method for describing filling material distribution in abandoned mine. Acknowledgements This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2017R1A2B4002031) and by the project funded by the Ministry of Oceans and Fisheries, Korea (D11603317H480000112).

Magnetotelluric exploration is one of geophysical methods for investigating the Earth’s deep interior. This method measures natural geoelectric and geomagnetic field values. Impedance is expressed by the relation between the measured electric fields and magnetic fields, and it is used to estimate the electromagnetic properties of the Earth’s deep interior. In the early stage, the geophysical responses at receiver was simply considered as responses from one-dimensional structure and the impedance was used in the form of scalar. As we consider three-dimensional structure nowadays, the impedance is mainly used in the form of matrix. Each component of the matrix is determined by various factors such as underground structure and surrounding environment. It is very important to know how these components reflect those factors since the components of the impedance are the basic information to estimate the interior of the earth. In this study, we focus on the topographic effects and correction with three-dimensional earth model for Gyeongju sites. As the Gyeongju area is surrounded by several mountains and faults, it has highly complicate topographies. However, the conventional topographic correction is not perfect for complex area because it is calculated in homogeneous earth model. In this study, we use the finite element methods using hexahedral and tetrahedral elements to examine the topographic correction method in complex topographies and three-dimensional anomalies. ACKNOWLEDGMENTS This work was supported by the Nuclear Safety Research Program through the Korea Foundation Of Nuclear Safety(KoFONS), granted financial resource from the Nuclear Safety and Security Commission(NSSC), Republic of Korea (No.1705010) and Korea Institute of Energy Technology Evaluation and Planning(KETEP) and the Ministry of Trade, Industry & Energy(MOTIE) of the Republic of Korea (No. 20168510030830).