5:15 PM - 6:30 PM
[MIS15-P03] Tsunami source estimation of paleotsunami deposits formed in the 17th century at Sekinehama, northern Shimokita Peninsula, Aomori Prefecture
This study reports the source estimation based on tsunami deposits at Sekinehama, Aomori Prefecture, northern Japan. In the 17th century, it is known that two huge tsunamis, 1611 CE Keicho tsunami and 17th century earthquake tsunami, have occurred along Japan and Kuril trenches, but their source areas, especially 1611 CE Keicho tsunami, are not well constrained yet. Besides, it is also uncertain whether two tsunamis were generated by discrete earthquakes or identical one. Their tsunami deposits have been identified along Sanriku coast and Sendai Plain and Tokachi to Nemuro coast along the Pacific coast of Hokkaido, respectively. Since our study area, Sekinehma, northern Shimokita Peninsula, is located between Kuril and Japan trenches, geological surveys in such location will give a significant information to solve the relationship of two huge tsunamis. Previous investigations revealed that there are widely-distributed a sand layer that are probable tsuami deposit showing the depositional age of the 17th century at Sekinehama. In this study, we conducted numerical simulations on tsunamis occurred in the 17th century in order to clarify tsunami source of the paleotsunami deposits at Sekinehama.
We used existing ten fault models which reconstruct the 1611 CE Keicho tsunami occurred along Japan Trench, 1677 CE Enpo-Sanriku and 17th century tsunamis occurred along Kuril Trench, and the tsunami caused by uplift of offshore active fault located on northern Shimokita Peninsula. To examine tsunami influence on Sekinehama, the ratio of computed tsunami inundation to the coastal lowland (<300 m from shoreline) was roughly evaluated near the place where probable tsunami deposits were found. In this study, calculations were performed using JAGRUS with an assumption that the topography in the 17th century is not much different from the present at Sekinehama. It is interpretated from the computed inundation rate at Sekinehama that large influences at the study area were given by three models which have >25 m slip amount along the south part of the Kuril Trench (>Mw 8.8; Ioki and Tanioka, 2016; Okamura and Namegaya, 2011; The Hokkaido Disaster Prevention Council, 2012) and one model which has 80 m slip amount along the north part of the Japan Trench (1611 CE Keicho tsunami model with Mw 9.0; Fukuhara and Tanioka, 2017). This suggests the possibility that the study area is inundated by a tsunami when its source is placed off the Pacific coast of Hokkaido rather than off Sanriku coast.
We then compared the calculated inundation rate for tsunami deposits distributed at coastal lowlands along Iburi coast in Hokkaido and east coast of Aomori Prefecture. These tsunami deposits are thought to be deposited in the 17th century, but their sources are still unknown. According to the computation results, the Kuril–Japan trench interlocking model can only explain the distribution of these tsunami deposits as well as that at Sekinehama. In addition, 1640 CE tsunami caused by Mt. Komagatake collapse should be also taken into consideration as a tsunami source at Sekinehama. However, there is no model restored a detailed process from mountain collapse to tsunami. As the result of preliminary simulation used a simple model by Nakanishi and Okamura (2019), 90% inundation rate and 4.6 m maximum height were calculated at Sekinehama, suggesting that the 1640 CE tsunami is one of the possible sources for the tsunami deposits at Sekinehama.
We inferred the Interlocking earthquake model and 1640 CE tsunami model caused by Mt. Komagatake eruption as the source of tsunami deposits at Sekinehama. For future, we plan to create highly accurate source models by changing fault parameters of mainly these two models to recover tsunami deposit distribution at study area.
This work was partly supported by the Sasakawa Scientific Research Grant from The Japan Science Society.
We used existing ten fault models which reconstruct the 1611 CE Keicho tsunami occurred along Japan Trench, 1677 CE Enpo-Sanriku and 17th century tsunamis occurred along Kuril Trench, and the tsunami caused by uplift of offshore active fault located on northern Shimokita Peninsula. To examine tsunami influence on Sekinehama, the ratio of computed tsunami inundation to the coastal lowland (<300 m from shoreline) was roughly evaluated near the place where probable tsunami deposits were found. In this study, calculations were performed using JAGRUS with an assumption that the topography in the 17th century is not much different from the present at Sekinehama. It is interpretated from the computed inundation rate at Sekinehama that large influences at the study area were given by three models which have >25 m slip amount along the south part of the Kuril Trench (>Mw 8.8; Ioki and Tanioka, 2016; Okamura and Namegaya, 2011; The Hokkaido Disaster Prevention Council, 2012) and one model which has 80 m slip amount along the north part of the Japan Trench (1611 CE Keicho tsunami model with Mw 9.0; Fukuhara and Tanioka, 2017). This suggests the possibility that the study area is inundated by a tsunami when its source is placed off the Pacific coast of Hokkaido rather than off Sanriku coast.
We then compared the calculated inundation rate for tsunami deposits distributed at coastal lowlands along Iburi coast in Hokkaido and east coast of Aomori Prefecture. These tsunami deposits are thought to be deposited in the 17th century, but their sources are still unknown. According to the computation results, the Kuril–Japan trench interlocking model can only explain the distribution of these tsunami deposits as well as that at Sekinehama. In addition, 1640 CE tsunami caused by Mt. Komagatake collapse should be also taken into consideration as a tsunami source at Sekinehama. However, there is no model restored a detailed process from mountain collapse to tsunami. As the result of preliminary simulation used a simple model by Nakanishi and Okamura (2019), 90% inundation rate and 4.6 m maximum height were calculated at Sekinehama, suggesting that the 1640 CE tsunami is one of the possible sources for the tsunami deposits at Sekinehama.
We inferred the Interlocking earthquake model and 1640 CE tsunami model caused by Mt. Komagatake eruption as the source of tsunami deposits at Sekinehama. For future, we plan to create highly accurate source models by changing fault parameters of mainly these two models to recover tsunami deposit distribution at study area.
This work was partly supported by the Sasakawa Scientific Research Grant from The Japan Science Society.