Browsing by Author "Nishimura, Y"

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    Erosion, deposition and landscape change on the Sendai coastal plain, Japan, resulting from the March 11, 2011 Tohoku-oki tsunami
    (Elsevier B.V., 2020-12-12) Richmond, B; Szczuciński, W; Chagué-Goff, C; Goto, K; Sugawara, D; Witter, R; Tappin, DR; Jaffe, BE; Fujino, S; Nishimura, Y; Goff, JR
    Case studies of recent tsunami impacts have proven to be extremely useful in understanding the geologic processes involved during inundation and return flow, and refining the criteria used to identify paleotsunami deposits in the geologic record. Here, we report on erosion, deposition and associated landscape change resulting from the March 11, 2011 Tohoku-oki tsunami along a nearly 4.5 km shore-normal transect on the coastal plain near Sendai, Japan. The study area on the broad, low-relief prograding coastal Sendai plain comprised a sand beach backed by ~ 3 m high sand dunes and a forest, a wetland, the Teizan canal, agricultural rice fields, buildings and roads. Field observations focused on measurements of tsunami flow characteristics (height and direction), mapping of erosion features and assessing sediment deposition based on shallow trenches at 50–100 m spacing. Recorded tsunami inundation heights reached up to about 11 m above mean sea level within the first 500 m from the shoreline and then ranged between 3 and 5 m for the next 2 km, gradually decreasing to about 3 m close to the inundation limit. The tsunami deposit generally thinned landward from an average maximum ~ 30 cm thick sand deposit in the coastal forest to a thin mud drape several mm thick near the inundation limit. A discontinuous sand-dominated sheet was prevalent to about 2800 m from the shoreline where mud content then gradually increased further landward eventually resulting in a mud-dominated deposit ranging from 3.5 cm to a few mm thickness. The overall thinning and fining of the deposit was often interrupted by localized features that led to complex sedimentological relationships over short distances. Satellite imagery taken on 14 March 2011, 3 days after the Tohoku-oki Tsunami shows prominent foreshore incisions with 100 s + meters spacing alongshore, a foredune ridge that underwent severe erosion and development of a prominent shore-parallel elongated scour depression. Our field survey in early May 2011 revealed that the foreshore recovered quickly with rapid post-tsunami sediment deposition from incident waves, whereas the dune–ridge complex had undergone only minor re-working from eolian processes. © 2020 Elsevier B.V
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    Field observations of erosion, deposition, and tsunami flow characteristics on the Sendai Coastal Plain after the March 2011, Tohoku-oki Tsunami, Japan
    (American Geophysical Union, 2011-11-05) Richmond, BM; Goto, K; Fujino, S; Nishimura, Y; Sugawara, D; Tappin, DR; Witter, RC; Jaffe, BE; Chagué-Goff, C; Szczuciński, W; Yulianto, E; Goff, JR
    Historical and instrumental data show that the Pacific coast of Mexico has been exposed to destructive tsunamis over at least the past 500 years. This coast is also affected by hurricanes generated in the eastern Pacific. The great 1985 Mexico earthquake and its aftershock generated tsunamis that affected the Ixtapa-Zihuatanejo and Michoacán coast. The purpose of our study was two-fold, a) to determine whether we could distinguish storm from tsunami deposits, and b) whether tsunami deposits from historical events are preserved in the tropical environments of the Ixtapa-Zihuatanejo coast. Two anomalous sand units in the Ixtapa estuary are interpreted as the result of high-energy marine inundation events that occurred in the last century. Several lines of evidence using a multi-proxy approach (historical studies, interviews with local witnesses, geomorphological and geological surveys, coring and trenching, and laboratory analyses including grain size, micropaleontology, geochemistry, magnetic susceptibility and radiometric dating) indicate the occurrence of two tsunamis that we link to local events: the 1985 Mexico and possibly the 1979 Petatlan earthquakes. We thereby provide the first onshore geological evidence of historical tsunamis on the Pacific coast of Mexico. © American Geophysical Union
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    Geochemical signatures and source material of marine incursion deposits
    (Elsevier, 2016-01-01) Chagué-Goff, C; Andrew, AS; Szczuciński, W; Goff, JR; Nishimura, Y
    The geochemical signature of the Tohoku-oki tsunami deposit and underlying soil was assessed two months, five months and seven months after the 11 March 2011 tsunami inundated the Sendai Plain. The extent of the recognisable sand deposit was traced up to 2.9 km inland while a mud deposit was found up to 4.65 km inland, representing 60% and nearly 95% of the maximum tsunami inundation, respectively. The limit of tsunami inundation was identified 4.85 km from the shore using geochemical marine markers (S and Cl) two months after the tsunami, in the absence of any sedimentological evidence. Concentrations of other geochemical markers (K, Ca, Sr) indicative of the marine incursion and associated minerals were found to decrease landward. δ13C and δ15N and C/N ratios suggested a mixture of terrestrial and marine organic sources in the sediment, while δ34S of sulphate reflected the marine source of water soluble salts. The chemical composition of the 869 AD Jogan tsunami sand deposit was characterised by high Sr and Rb concentrations and was comparable to that of the Tohoku-oki tsunami deposit, suggesting that the sources of sediment may be similar. Marked decreases in S and Cl with time indicated that rainfall resulted in the leaching of salts from the sandy sediments. However, both S and Cl markers as well as Sr were still well preserved in the muddy sediments and underlying soil beyond the limit of the recognisable sand deposit seven months after the tsunami. This suggests that geochemical indicators may well be useful in identifying the extent of historical and palaeotsunamis by determining the marine origin of fine grained sediments beyond the limit of recognisable sand deposition, in particular when marine microfossils are sparse or lacking as is the case on the Sendai Plain. This would allow researchers to redraw palaeotsunami inundation maps and re-assess the magnitude of events such as the Jogan tsunami and other palaeotsunamis, not only on the Sendai Plain but also elsewhere around the world. This has important implications for tsunami risk assessment, hazard mitigation and preparedness.© 2012 Elsevier B.V.
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    Geochemical signatures up to the maximum inundation of the 2011 Tohoku-oki tsunami — Implications for the 869 AD Jogan and other palaeotsunamis
    (Elsevier B.V., 2012-12-30) Chagué-Goff, C; Andrew, AS; Szczuciński, W; Goff, JR; Nishimura, Y
    The geochemical signature of the Tohoku-oki tsunami deposit and underlying soil was assessed two months, five months and seven months after the 11 March 2011 tsunami inundated the Sendai Plain. The extent of the recognisable sand deposit was traced up to 2.9 km inland while a mud deposit was found up to 4.65 km inland, representing 60% and nearly 95% of the maximum tsunami inundation, respectively. The limit of tsunami inundation was identified 4.85 km from the shore using geochemical marine markers (S and Cl) two months after the tsunami, in the absence of any sedimentological evidence. Concentrations of other geochemical markers (K, Ca, Sr) indicative of the marine incursion and associated minerals were found to decrease landward. δ13C and δ15N and C/N ratios suggested a mixture of terrestrial and marine organic sources in the sediment, while δ34S of sulphate reflected the marine source of water soluble salts. The chemical composition of the 869 AD Jogan tsunami sand deposit was characterised by high Sr and Rb concentrations and was comparable to that of the Tohoku-oki tsunami deposit, suggesting that the sources of sediment may be similar. Marked decreases in S and Cl with time indicated that rainfall resulted in the leaching of salts from the sandy sediments. However, both S and Cl markers as well as Sr were still well preserved in the muddy sediments and underlying soil beyond the limit of the recognisable sand deposit seven months after the tsunami. This suggests that geochemical indicators may well be useful in identifying the extent of historical and palaeotsunamis by determining the marine origin of fine grained sediments beyond the limit of recognisable sand deposition, in particular when marine microfossils are sparse or lacking as is the case on the Sendai Plain. This would allow researchers to redraw palaeotsunami inundation maps and re-assess the magnitude of events such as the Jogan tsunami and other palaeotsunamis, not only on the Sendai Plain but also elsewhere around the world. This has important implications for tsunami risk assessment, hazard mitigation and preparedness. © 2020 Elsevier B.V.
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    Impact of tsunami inundation on soil salinsaltion - up to one year after the 2011 Tohoku-okitsunami
    (Springer, 2013-09-27) Chagué-Goff, C; Wong, HKY; Sugawara, D; Goff, JR; Nishimura, Y; Beer, J; Szczuciński, W; Goto, K
    The long-term effect of tsunami inundation on soil salinisation was assessed following the 2011 Tohoku-oki tsunami in two areas on the Sendai Plain, near Sendai airport in the Miyagi Prefecture and Matsukawa-ura near Soma in the Fukushima Prefecture. Data gathered over four sampling seasons 2, 5, 9 and 11 months after the tsunami near Sendai airport show that the salt content generally decreased with time. Concentrations were nevertheless higher in February 2012 than in October 2011, probably due to capillary action and evaporation following long periods with little precipitation in the winter, while the lower concentrations in October were attributed to dilution due to intense rainfall prior to the sampling period. In February 2012, the area with chloride concentrations over the guidelines for the establishment of rice seedlings still extended for nearly 1 km between 2.45 and 3.33 km inland. Chloride concentrations also reached the guideline values at the land surface 1.71 km inland. This corresponded to the limit of the area deemed not suitable for rice production by local rice farmers. However, recent observations revealed that rice crops were not only halted in 2011 but also in 2012, probably due to high salinisation of soil and/or surface and groundwater. Our study shows that soil salinisation was still recorded to nearly 15 cm depth in areas with fine-grained organic-rich soil ~2.5 km from the shoreline 11 months after the tsunami, and that water-leachable ions were preferentially retained in organic-rich muddy sediment and soil, reflecting the long-term impact of tsunami inundation. In Matsukawa-ura, salt crusts still covered the area flooded by the tsunami in February 2012 and both the soil and muddy tsunami deposit were characterised by high chloride and sulphate concentrations. The latter might also lead to sulphide toxicity. Remediation measures have been implemented in certain areas, but further research needs to be carried out to test the effectiveness of the measures being used to allow rice production to resume. © 2014, Springer Science+Business Media Dordrecht.
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    Initial field survey report of the 2011 East Japan Tsunami in Sendai, Natori adn Iwanuma Cities
    (UNESCO-IOC, 2011-07-10) Sugawara, D; Goto, K; Chagué-Goff, C; Fujino, S; Goff, JR; Jaffe, BE; Nishimura, Y; Richmond, B; Szczuciński, W; Tappin, DR; Witter, R; Yuliento, E
    The East Japan Earthquake (Mw 9.0) and associated tsunami struck the Pacific coast of eastern Japan on March 11th, 2011 at 2:46 p.m. (Japan Standard Time). Maximum run-up heights reached about 40 m along the Sanriku region’s coast and around 10 m on the Sendai coastline. The coasts of Iwate, Miyagi and Fukushima Prefectures in particular were badly damaged, and a considerable amount of time and money will be required to restore these areas. Tsunami inundation up to 5 km inland occurred across the Sendai Plain, which remained partly flooded for several weeks after the event. Some areas were still under water 2 months after the earthquake, and are likely to remain flooded for some time as a result of subsidence. The Disaster Control Research Center at Tohoku University conducted scientific research of the inundated coastal plains of Sendai, Natori and Iwanuma Cities in collaboration with other research institutes from Japan and overseas with the support of UNESCO-IOC (Intergovernmental Oceanographic Commission). Data and samples collected during the field survey are now being analyzed by various institutes around the World. This report is a summary of our field survey that focused on an area to the north of Sendai Airport. Radioactivity data recorded at the time of survey are also provided.
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    Modern and possible paleotsunami deposits in Samenoura, Sanriku Coast, and their relation to tsunami source mechanisms
    (Japan Geoscience Union Meeting, 2014-05-02) Sugawara, D; Nishimura, Y; Goto, K; Goff, JR; Jaffe, BE; Richmond, B; Chagué-Goff, C; Szczuciński, W; Yokoyama, Y; Miyairi, Y; Sawada, C
    Samenoura is situated in the bay head of a small inlet on the Pacific coast of Oshika Peninsula, one of the nearest places to the epicenter of the 2011 Tohoku-oki Earthquake. According to the Joint Survey Group, wave heights were measured at more than 20 m near the coastline. This area was severely damaged as a result of both co-seismic subsidence and tsunami inundation. We carried out field surveys of the Tohoku-oki and paleotsunami deposits at Samenoura in March, May and October 2013. Sandy deposits laid down by the Tohoku-oki tsunami were up to 20 cm thick at locations with an elevation greater than 10 m, and were several cm thick within the forest higher up. The tsunami deposit also contained numerous shell fragments and foraminifera. Although some possible sources of the tsunami deposits can be attributed to narrow sandy beaches near the study area, the deposition of such a thick sandy deposit is more or less enigmatic, considering the steep Ria-type coastal topography.Using a gouge auger and geoslicer, we found at least two sand layers intercalated within muddy sediments. A volcanic ash layer, which corresponds to the AD 915 Towada-a tephra, was also identified from a horizon between these sand layers. The underlying sand layer was most probably laid down by the 869 Jogan earthquake tsunami, one of the large-scale events known to have affected the region. Previous studies of the Jogan tsunami have proposed several possible source models that involve an interplate thrust earthquake. Given that the local bathymetry and topography of Samenoura Bay may be sensitive to the waveform of a large-scale tsunami, paleotsunami deposits found from this area may be the key to determining the source mechanisms of events on the Sanriku Coast.In this presentation, the possible correlation of the sandy deposits with known paleotsunami events based on detailed radiocarbon dating is discussed. The hydrodynamic character and processes of tsunami sediment erosion and deposition in Samenoura Bay are analyzed using numerical modeling of both interplate and outer-rise earthquake scenarios. © Japan Geoscience Union Meeting, 2014.
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    New insights of tsunami hazard from the 2011 Tohoku-oki event
    (Elsevier, 2011-12-01) Goto, K; Chagué-Goff, C; Fujino, S; Goff, JR; Jaffe, BE; Nishimura, Y; Richmond, B; Sugawara, D; Szczuciński, W; Tappin, DR; Witter, R; Yulianto, E
    We report initial results from our recent field survey documenting the inundation and resultant deposits of the 2011 Tohoku-oki tsunami from Sendai Plain, Japan. The tsunami inundated up to 4.5 km inland but the >0.5 cm-thick sand deposit extended only 2.8 km (62% of the inundation distance). The deposit however continued as a mud layer to the inundation limit. The mud deposit contained high concentrations of water-leachable chloride and we conclude that geochemical markers and microfossil data may prove to be useful in identifying the maximum inundation limit of paleotsunamis that could extend well beyond any preserved sand layer. Our newly acquired data on the 2011 event suggest that previous estimates of paleotsunamis (e.g. 869 AD Jogan earthquake and tsunami) in this area have probably been underestimated. If the 2011 and 869 AD events are indeed comparable, the risk from these natural hazards in Japan is much greater than previously recognized. (c) 2011 Elsevier