17:15 〜 18:30
[MIS15-P05] 秋田県沿岸域における1983年日本海中部地震津波による堆積物の分布と特徴
キーワード：1983年日本海中部地震、津波堆積物、微化石
The Nihonkai-chubu earthquake occurred off the western coast of Noshiro City in Akita Prefecture, northeastern Japan on 26th May 1983. The tsunami due to the earthquake caused widespread damage to the west coastal area of the northeastern Japan, including Akita coastal region, depositing sand and mud transported by the tsunami. We conducted geological surveys from December 2019 to January 2020 within the pine-based coastal protecting forests planted along the coastal region of Akita Prefecture in the period of 1948 to 1970. Sand layers that exhibit inland thinning were observed in the soil at a depth of <10 cm at Happo Town, Noshiro City and Mitane Town, Akita Prefecture. As this sand layer contains well preserved brackish-marine diatoms such as Fallacia sp. and Thalassiosira nanolineata, it is highly probable that it was transported inland from the coast; a continuity distribution was confirmed from the coast to ~300 m inland only within the coastal protecting forest. According to historical records, we postulate that this sand layer is the result of deposition by the 1983 tsunami, as the area could not have been reached by any means other than the tsunami produced by the Nihonkai-chubu Earthquake. There are few reports of tsunami deposits with specific ages in Japan, so they are an important historical record of past disasters. It has been noted that tsunami deposits lose their sedimentary structures and constituents over time due to changes in weather conditions; therefore, the samples of these deposits can also be used to study the weathering processes of tsunamis deposits.
On the other hand, we also recognized another thin sand layer upper the tsunami deposits. There is a high probability that this sand layer was formed by the strong wind of the Typhoon 9119 reached in 28th September 1991, because no major floods or tsunamis caused damage to our study area have occurred after the 1983 tsunami event.
In this presentation, we report the distribution and characteristics of deposits from the tsunami generated by the 1983 Nihonkai-chubu earthquake and the eolian sand formed by the Typhoon 9119 recognized in coastal protecting forests planted along the Happo Town, Noshiro City and Mitane Town.
On the other hand, we also recognized another thin sand layer upper the tsunami deposits. There is a high probability that this sand layer was formed by the strong wind of the Typhoon 9119 reached in 28th September 1991, because no major floods or tsunamis caused damage to our study area have occurred after the 1983 tsunami event.
In this presentation, we report the distribution and characteristics of deposits from the tsunami generated by the 1983 Nihonkai-chubu earthquake and the eolian sand formed by the Typhoon 9119 recognized in coastal protecting forests planted along the Happo Town, Noshiro City and Mitane Town.