Details

Autor(en) / Beteiligte

• Matsumoto, Dan
• Sawai, Yuki
• Tanigawa, Koichiro
• Fujiwara, Osamu
• Namegaya, Yuichi
• Shishikura, Masanobu
• Kagohara, Kyoko
• Kimura, Haruo

Titel

Tsunami deposit associated with the 2011 Tohoku-oki tsunami in the Hasunuma site of the Kujukuri coastal plain, Japan

Ist Teil von

• The island arc, 2016-09, Vol.25 (5), p.369-385

Ort / Verlag

Tokyo: Blackwell Publishing Ltd

Erscheinungsjahr

2016

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• We describe the detailed sedimentary characteristics of a tsunami deposit associated with the 2011 Tohoku‐oki tsunami in Hasunuma, a site on the Kujukuri coastal plain, Japan. The thick tsunami deposit was limited to within 350 m from the coastline whereas the inundation area extended about 1 km from the coastline. The tsunami deposit was sampled by excavation at 29 locations along three transects and studied using peels, soft‐X imaging and grain‐size analysis. The deposit covers the pre‐existing soil and reached a maximum measured thickness of 35 cm. It consists mainly of well‐sorted medium to fine sand. On the basis of sedimentary structures and changes in grain size, we divided the tsunami deposit into several sedimentary units, which may correspond to multiple inundation flows. The numbers of units and their sedimentary features vary among the three transects, despite the similar topography. This variation implies a considerable influence of local effects such as elevation, vegetation, microtopography, and distance from footpaths, on the tsunami‐related sedimentation. 千葉県九十九里平野蓮沼海岸に形成された2011年東北太平洋沖地震津波堆積物の特徴 古津波堆積物をより精度よく識別するためには, 現世の津波堆積物の特徴をモダンアナログとして利用することが必要である. そこで, 本研究では2011年東北地方太平洋沖地震による津波によって千葉県九十九里平野の蓮沼海岸に形成された津波堆積物を対象に, 海岸線に直交する3本の測線上で調査を行い, その層厚変化や粒度などの特徴を明らかにした. この地域では内陸に向かって薄層化する砂質の津波堆積物が海岸線から約350 mまでの範囲にみられた. また粒度や堆積構造の特徴から2–4つの級化ユニットに区分された. 調査地周辺では最大4回程度の津波の遡上が観察されており, 各ユニットは遡上イベントに対応して形成された可能性が示唆される. This article reports detailed description of a 2011 Tohoku‐oki tsunami deposit in the Hasunuma site, such as thickness, sedimentary structures and grain‐size distribution. We discuss lateral and vertical changes of such characteristics, and relationship with the sedimentation by the tsunami inundation flows.