Great earthquake at 7.3 ka inferred from tsunami deposits in the Sukumo Bay area, Southwestern Japan

Nanayama, Futoshi; Tsuji, Tomohiro; Yamaguchi, Tatsuhiko; Kondo, Yasuo; Ikeda, Michiharu; Nakanishi, Toshimichi; Miwa, Makiko; Hongo, Chuki; Furusawa, Akira; Kuwahata, Mitsuhiro

doi:10.1111/iar.12422

Cited by 3 publications

(2 citation statements)

References 62 publications

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“…A fragment of Cyphastrea sp. with an age of 7.0 ka was found in a Holocene sediment core from Sukumo Bay in Kochi Prefecture (32.9°N) (Nanayama et al 2021). A colony of D. speciosa indicates that initiation of formation of the Numa coral bed in Chiba Prefecture dates back to 7.8 ka (Sato et al 1968).…”

Section: Resultsmentioning

confidence: 96%

Are the coral mounds of the Kushimoto area, Wakayama Prefecture, Japan, submerged Holocene reefs?

Hongo

Asami

Iryu

2023

Galaxea, Journal of Coral Reef Studies

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We investigated coral mounds at 10-15 m water depth in the Kushimoto area of Wakayama Prefecture, Japan. These mounds may be submerged Holocene reefs, but no evidence has yet been presented to support this hypothesis. We collected two cores and three dead corals from one of the mounds. Our results show that Miocene bedrock lies only 0.1 m below the surface of the mound, and in situ corals form a thin veneer above the antecedent substrate. Radiocarbon dating of four coral samples yielded ages of 112 cal. yr BP to modern. These findings indicate that the mounds are not submerged Holocene reefs. The sea-surface temperatures in February are <18°C in the study area and would be insufficient for rapid precipitation of calcium carbonate by coral species. Given that the study area faces the open ocean, it is probable that the corals are frequently dislodged by high wave forces during intense tropical cyclones and/or tsunamis. Consequently, the study area appears to lie beyond the distributional limit of coral reefs during the Holocene.

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Section: Resultsmentioning

confidence: 96%

Are the coral mounds of the Kushimoto area, Wakayama Prefecture, Japan, submerged Holocene reefs?

Hongo

Asami

Iryu

2023

Galaxea, Journal of Coral Reef Studies

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“…Because of the sporadic distribution of marine terraces, RSL records are scattered on southern Shikoku Island. Other studies have identified pre-historical earthquake-related sediments on Shikoku Island (Iwai et al, 2004;Nanayama et al, 2020Nanayama et al, , 2021Shimada et al, 2019;Tanigawa et al, 2018). Iwai et al (2004) studied piston core sediments from off Cape Muroto and identified 31 seismoturbidite layers that may have been generated during earthquake events in the last 7000 years.…”

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confidence: 99%

Middle Holocene relative sea‐level changes and vertical tectonic crustal movements on Shikoku Island near the Nankai Trough, Japan

et al. 2022

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The Philippine Sea plate subducts beneath the Eurasia plate at the Nankai Trough, northwestern Pacific, causing crustal deformation, mega‐thrust earthquakes, and tsunami events. Shikoku Island, 150 km northwest of the trough, experiences both coseismic and interseismic deformation. Coastal sediments potentially record vertical crustal movements as relative sea level (RSL) changes. We studied sedimentary facies and microfossil ostracodes in core SKM from southwestern Shikoku Island for evidence of middle Holocene tsunami events and deformation. The core sediments included nine event layers corresponding to storm or tsunami events. Using modern analog techniques, we estimated RSLs from the ostracode assemblages of core SKM and 13 other cores from Shikoku Island and the surrounding region. Then, we subtracted RSL changes due to glacio‐hydro isostatic adjustment from the estimated RSLs to estimate vertical tectonic movement rates in these cores between 8.6 and 4.7 ka. The inferred RSL changes suggest that the Sukumo site has experienced both uplift and subsidence since 8.6 ka. Before 6.6 ka, rates of tectonic crustal movement were higher than the modern‐day rate, and its spatial distribution also differed. After 6.6 ka, tectonic crustal movement showed a similar spatial pattern and occurred at rates close to the modern day interseismic rate. The spatial pattern and rates of tectonic crustal movement could be caused by changes in rupture areas between the Eurasia and the Philippine Sea plates beneath the Shikoku Island and in stress condition of the asthenosphere. Some of the vertical displacements can be explained by the movements of local active faults.

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Pollen analysis of sediment core from Yukashigata Lagoon, in western Japan reveals paleovegetation changes during the past 1500 year

Fujiki,

Nakanishi,

Yamada

et al. 2024

Preprint

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A 292-cm-long sediment core was collected from the center of Yukashigata Lagoon using a Mackereth air-pressure piston corer. Pollen analysis with radiocarbon dating of this sediment core was conducted to reconstruct the surrounding paleoenvironment. The results revealed a decrease in evergreen broadleaf tree pollen grains, an increase in herb pollen grains and fern spores, and a slight increase in charcoal fragments around 1100 cal CE, suggesting the onset of human impact on vegetation around this time. A major vegetation shift occurred around 1300 cal CE, marked by a rapid increase in Pinus pollen grains, herb pollen grains, and fern spores, along with a decrease in evergreen broadleaf tree pollen grains. The latter change suggested large-scale destruction of vegetation. Subsequently, tree pollen grains continued to decline, with a further decrease around 1550 cal CE, perhaps caused by the extensive use of Kumano timber for the construction of castles and temples by Sengoku-period warlords. Much of this timber was supplied by the Kishu Domain. However, as the Kishu supply of high-quality timber began to deplete, the warlords shifted to a policy of forest protection and cultivation, banning the felling of six tree species. As a result, the abundance of Pinus and Cryptomeria pollen grains sharply increased from around 1650 cal CE, as did that of evergreen broadleaf tree pollen grains which indicated a transition from compensatory vegetation to evergreen broadleaf forest from around 1950 cal CE. This vegetation recovery appears to have been linked to increasing reliance on plant-based fuels as fossil fuels became more widely adopted.

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Great earthquake at 7.3 ka inferred from tsunami deposits in the Sukumo Bay area, Southwestern Japan

Cited by 3 publications

References 62 publications

Are the coral mounds of the Kushimoto area, Wakayama Prefecture, Japan, submerged Holocene reefs?

Are the coral mounds of the Kushimoto area, Wakayama Prefecture, Japan, submerged Holocene reefs?

Middle Holocene relative sea‐level changes and vertical tectonic crustal movements on Shikoku Island near the Nankai Trough, Japan

Pollen analysis of sediment core from Yukashigata Lagoon, in western Japan reveals paleovegetation changes during the past 1500 year

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