磁気特性を用いた砂質海岸での鉄製品の埋設物の検出―岡山県瀬戸内市矢寄ヶ浜の例―

Abstract

In order to detect buried iron items in a natural sand beach, we conducted a magnetic survey with an Overhauser magnetometer. First, a three-meter-long survey line was laid at Yayorigahama Beach in Okayama Prefecture. A steel can, a stainless steel knife, and a plug-in multi-tap were buried at 10 cm. Magnetic field intensity (MFI) and the magnetic susceptibility (MS) were measured on the beach surface. The MS values indicate a relatively higher value at the site where the steel can was buried 10 cm in burial depths, while such an increase was found at the depths of 20 cm, 30 cm, 40 cm and 50 cm. The peak of MFI could be recognized at the depths of 10 cm to 40 cm. This implies that the MFI test with an Overhauser magnetometer is more effective than the MS measurement. Magnetic anomalies of MFI were recognized on another survey line in Yayorigahama Beach where reinforcing iron bars were found at a depth of 90 cm. Our results indicate that the hidden iron items could be detected using an Overhauser magnetometer in the sand beach.