Geomorphic hazard along coastal plains in Central Ryukyus(Amami Oh-shima and Okinawa Islands)
| Autor: | Kimura, Kazuo, Department of Integrated Arts and Sciences |
|---|---|
| Jazyk: | japonština |
| Rok vydání: | 2016 |
| Předmět: | |
| Zdroj: | 沖縄工業高等専門学校紀要 = Bulletin of National Institute of Technology, Okinawa College. 10:29-40 |
| ISSN: | 1881-722X |
| Popis: | 1960年チリ地震津波の被災地を主な対象として、奄美大島および沖縄島における沿岸部の災害危険度と地形種・ 地形場との関係を検討した。その結果、従来から知られていた、リアスおよびそれに類する海岸地形や、沈水した旧河道とその周辺などで、被害が拡大しやすい傾向は、亜熱帯島嶼でも同様であることが確かめられた。そもリアスのような地形はサンゴ礁形成には適さないため、亜熱帯固有の津波減衰効果も小さい。またサンゴ礁海岸においては、連続性の良い裾礁が分布する範囲では比較的被害が少なかったが、小規模なエプロン礁が分布する地域では、 礁原の狭間に津波が集中して波高・遡上高が増幅され、局所的に被害が大きくなる傾向が認められた。近年の広範な埋立地造成は、こうした亜熱帯特有の地形特性を消失せしめ、津波の波高を増幅する急峻な海底斜面に直面し、 なおかつ人工水路を通じて津波のエネルギーを特定の場へ集中させるような地形場を、新たに産み出している。津波に代表される沿岸災害リスクの判定には、現在のハザードマップの基準である地形量(標高)による評価だけでなく、地形場・地形種のような質的な吟味を加味した改善が求められる。 This case study of the 1960 Chilean earthquake tsunami aims to show the relation between geomorphic characteristics and disaster intensity in Central Ryukyus, which are located in a sub-tropic island arc. The Amami Oh-sima Island is mainly surrounded by rias. Therefore, coastal plains such as Naze, Kominato, Sumiyo, Koniya are fragile for tsunami disasters. In northern part of Okinawa Island, submerged grabens form Taira Bay, Arime Bay, Oh-ura Bay, and offshore of Makiya and Nago areas. Geomorphic risk of those bays is similar to that of rias coast. Southern part of Okinawa Island was widely surrounded by fringing reefs in 1960. Those areas were less damaged by the tsunami in comparison with the above-mentioned regions. This shows that fringing reef is effective barrier for tsunami and similar coastal disasters. However, the highest tsunami in Central Ryukyus was also observed along a coast with coral reefs. In Kasari, which is north end of Amami Oh-shima, there are some apron reefs. The gap of apron reefs can concentrate tsunami energy, therefore, Kasari area was deeply inundated by the 1960 tsunami. Similarly, tsunami fluid concentrate to submerged valley. The wide inundation in Ishikawa of central Okinawa was caused by the effect of a submerged channel. During the last half-century, those coastal environments have been changed dramatically. Today, the most serious bottleneck for coastal disaster prevention is reclaimed lands. They have been eliminated fringing reefs, the guardian of costal life. They also produce tsunami-leading artificial channels. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|