Delineating the Bonghwang earth castle and Royal Palace of Geumgwan Gaya Kingdom using multiple geophysical techniques

Geophysical techniques such as electrical resistivity, ground penetrating radar (GPR), gravity, magnetic, and seismic surveys are useful for prospecting archaeological remains. In this study, we delineated the domain and underground structure of the Bonghwang earth castle and the Royal Palace of the Geumgwan Gaya Kingdom, using multiple geophysical surveys (magnetic, electromagnetic, GPR, and electrical resistivity). Based on the results, the Bonghwang earth castle was extended from a small hill branching from the northern end of the Bonghwangdae hill with a width of 20 m to the hill on the southeast end with a width of slightly over 40 m. The Royal Palace inside the Bonghwang earth castle was further explored using magnetic and GPR surveys. As a result low magnetic values are surrounded radially by high magnetic values at multiple independent locations in an irregular shape in the centre of the Royal Palace. In contrast, the high anomaly zone near the centre of the Royal Palace had a rectangular or ellipsoidal shape, necessitating a clear need for archaeological investigation and excavation in the future.