Browsing by Author "Witter, R"

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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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    Geological and geochemical field survey on the Sendai Plain following the 11 March 2011 Tohoku-Oki Tsunami
    (American Geophysical Union, 2011-12-05) Chagué-Goff, C; Goto, K; Fujino, S; Nishimura, D; Szczuciński, W; Rishmond, B; Tappin, D; Jaffe, BE; Witter, R; Yulianto, K; Goff, JR
    A post-tsunami survey was carried out in May 2011 by members of a UNESCO-IOC International Tsunami Survey Team. The geological and geochemical survey was carried out along a transect extending 4.5 km inland north of Sendai airport, and focused on tsunami flow characteristics, sedimentation and erosion, as well as assessing the impact of saltwater contamination on the paddy fields . Tsunami inundation in this area reached c. 4.5 km inland, and the limit was marked by the elevated Tobu Highway, except where underpass structures allowed inundation further inland. The tsunami deposit generally thinned and fined inland, with the sandy deposit thinning landward from about 30 cm thickness in the coastal forest to less than 0.5 cm c. 2.8 km inland. Rip-up clasts were observed mostly near the base of the sandy deposits. Further inland, the deposit was dominated by mud, although it contained thin sand laminae one to a few grain-thick up to the limit of inundation near Tobu Highway. The thickness of the tsunami deposit was found to show large variability over short distances. Erosion and liquefaction features were also commonly observed. Ponded water was reported between the coastal forest and up to 2.6 km inland, while salt crusts were observed on numerous rice paddy fields up to the limit of tsunami inundation, where the water had evaporated. Conductivity measurements of ponded water, canals, irrigation and drainage channels revealed that the water was still saline to brackish, despite >60 mm of precipitation in the two months since the tsunami. Elevated concentrations of water-leachable chloride (salt) were measured both in mud and sand deposits, where seawater had stagnated and evaporated.
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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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    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