Details

Autor(en) / Beteiligte

• Kawakami, Gentaro
• Nishina, Kenji
• Kase, Yoshihiro
• Tajika, Jun
• Hayashi, Keiichi
• Hirose, Wataru
• Sagayama, Tsumoru
• Watanabe, Tatsuya
• Ishimaru, Satoshi
• Koshimizu, Ken'ichi
• Takahashi, Ryo
• Hirakawa, Kazuomi

Titel

Stratigraphic records of tsunamis along the Japan Sea, southwest Hokkaido, northern Japan

Ist Teil von

• The island arc, 2017-07, Vol.26 (4), p.n/a

Ort / Verlag

Melbourne: John Wiley & Sons Australia, Ltd

Erscheinungsjahr

2017

Quelle

Wiley Online Library - AutoHoldings Journals

Beschreibungen/Notizen

• The stratigraphy of tsunami deposits along the Japan Sea, southwest Hokkaido, northern Japan, reveals tsunami recurrences in this particular area. Sandy tsunami deposits are preserved in small valley plains, whereas gravelly deposits of possible tsunami origin are identified in surficial soils covering a Holocene marine terrace and a slope talus. At least five horizons of tsunami events can be defined in the Okushiri Island, the youngest of which immediately overlies the Ko‐d tephra layer (1640 AD) and was likely formed by the historical Oshima‐Ohshima tsunami in 1741 AD. The four older tsunami deposits, dated using accelerator mass spectrometry 14C, were formed at around the 12th century, 1.5–1.6, 2.4–2.6, and 2.8–3.1 ka, respectively. Tsunami sand beds of the 1741 AD and circa 12th century events are recognized in the Hiyama District of Hokkaido Island, but the older tsunami deposits are missing. The deposits of these two tsunamis are found together at the same sites and distributed in regions where wave heights of the 1993 tsunami (Hokkaido Nansei‐oki earthquake, Mw = 7.7) were less than 3 m. Thus, the 12th century tsunami waves were possibly generated near the south of Okushiri Island, whereas the 1993 tsunami was generated towards the north of the island. The estimated recurrence intervals of paleotsunamis, 200–1100 years with an average of 500 years, likely represents the recurrence interval of large earthquakes which would have occurred along several active faults offshore of southwest Hokkaido. 北海道南西部の日本海沿岸域における津波堆積物の層序から, この地域の津波履歴を明らかにした. 砂質津波堆積物は小河川の谷底低地に, 礫質津波堆積物は完新世段丘や崖錐表層の土壌中に認められた. 奥尻島では5層準の津波イベントが識別され, 最も若いものは駒ケ岳d火山灰層(西暦1640年降灰)の直上に位置することから, 西暦1741年の渡島大島噴火に伴う津波堆積物と考えられる. それより古いものは放射性炭素年代により12世紀頃, 1.5∼1.6 ka, 2.4∼2.6 ka, 2.8∼3.1 kaの形成と推定された. 1741年の津波と12世紀の津波による堆積物は同一地点に認められるが, そこでは1993年の北海道南西沖地震による津波の高さが3 mに満たない. したがって12世紀の津波の波源は1993年の津波の波源とは異なり, 奥尻島の南側にあったと推定される. 調査地域における古津波の発生間隔は200∼1100年であり, これは北海道南西沖における大地震の発生間隔を示すと考えられる. Tsunami deposits on the Japan Sea coast of southwest Hokkaido, northern Japan, provide information about recurrences of tsunamis in the area. Prehistoric tsunamis occurred at 12th century, 1.5–1.6, 2.4–2.6, and 2.8–3.1 ka. The average 500 year tsunami recurrence interval probably reflects the interseismic period of large earthquakes generated by several offshore faults near southwest Hokkaido.