| 講演要旨(和文) | | 沿岸域で適用可能な自己修復能力を持つ人工岩盤に関する研究は，環境に負荷を与えず低コストでの海岸堤防を建設する上で重要と考えられる。自然材料（微生物，砂，貝殻，サンゴ片，海藻など）を用いて厳しい気象条件に耐えうる強度の人工岩盤を比較的短期間で形成させることを目標に研究が進められている．その一つのモデルとして，熱帯・亜熱帯地域のサンゴ礁沿岸域に存在するビーチロックが着目されているが，その地下構造に関する調査事例はほとんどない．そこで，沖縄県内に数多く分布が確認されているビーチロックの地下構造を明らかにすることを目的に，地表面から非破壊でビーチロックおよびその周辺の地下構造を探査できる電気探査法および表面波探査法を行った．また，ビーチロック試料を用いた室内試験によりその物理特性を計測した．その結果，ビーチロックの厚さ1m程度で，中新世の国内堆積軟岩の物理特性に類似することが分かった． |
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| | 講演要旨(英文) | | Previous studies of beachrocks have been focused on the geochemistry. However, more knowledge on the chemical and physical properties are needed to elucidate its formation mechanism. In this study, a DC electrical survey and a seismic surface survey were conducted to detect the underground structure of the beachrocks in Yagaji Island, Okinawa, Japan. This is a first attempt at conducting multiple geophysical surveys to investigate Beachrock. In each survey, one survey line was set perpendicular to the seashore and two survey lines were set horizontal to the seashore. The results of each survey were shown in resistivity and seismic surface wave velocity sections. Furthermore, laboratory tests were conducted to measure the porosity, resistivity, and elastic wave velocity of the beachrock sample collected from this study site in order to estimate the effectiveness of the surveys. There was a superior correlation between both the sections and the date of the study site. Both surveys showed the vertical and horizontal extent, the resistivity, and the shear wave velocity of the rock. From these results, it is deduced that geophysical prospecting is extremely effective for studying the distribution of beachrocks. This paper shows the features of beachrocks in this area and the knowledge obtained from this study of geophysical prospecting for beachrocks. |
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