A5054210736- earthquake and tectonic studies
- Geology and Paleoclimatology Research
- Methane Hydrates and Related Phenomena
- Geological formations and processes
- Seismology and Earthquake Studies
- Geological and Geochemical Analysis
- Marine and environmental studies
- Geochemistry and Geologic Mapping
- Isotope Analysis in Ecology
- Earthquake and Disaster Impact Studies
- Archaeology and ancient environmental studies
- Landslides and related hazards
- Flood Risk Assessment and Management
- Coastal and Marine Dynamics
- Hydrology and Watershed Management Studies
- Paleontology and Stratigraphy of Fossils
- Earthquake and Tsunami Effects
- Radioactive contamination and transfer
- Earthquake Detection and Analysis
- Geological Studies and Exploration
- Geomagnetism and Paleomagnetism Studies
- Diatoms and Algae Research
- Disaster Management and Resilience
- Financial Crisis of the 21st Century
- Radioactivity and Radon Measurements
Geological Survey of Japan
2016-2025
National Institute of Advanced Industrial Science and Technology
2015-2025
Kobe University
2010-2012
Abstract A sparsely documented tsunami in 1454 may subdivide the recurrence interval between 869 and 2011 tsunamis near Sendai, as judged from geomorphic, stratigraphic, archival evidence. Pond‐filled breaches cut across beach ridges on century‐old topographic maps. The basal pond deposit one of these postdates 1454. Stratigraphy Sendai Plain includes a sand sheet that contains marine brackish diatoms. Radiocarbon ages suggest dates to 1406–1615 (2 σ ), written records for this Tohoku...
Abstract This study reports sedimentological and paleontological features of deposits left by the 2024 Noto Peninsula tsunami in Suzu City, Japan. Tsunami were found up to 70 m inland from post-tsunami shoreline along our transect. The collected at five locations for observation Soft X-ray CT images, grain-size analysis, diatom analysis. images identified that stratigraphic units (Units 1–5) most seaward location (SZ1) with faint laminae other (SZ2–4). Grain-size analysis showed generally...
This study presents relative sea-level (RSL) change from 11,200 to 500 cal. BP in the Toyooka Basin, western Japan. Diatom assemblage and sedimentary sulfur analyses were performed for 32 sediment cores obtained thick Holocene fluvial marine deposits. An age model was constructed based on tephrochronology 31 radiocarbon ages elevations of −46.85 +1.51 m 19 cores. The RSLs Basin are −31.05 elevation at 10,000 cal BP, above −4.00 7900 −0.47 6700 +0.15 3300 BP. A rapid rise, a rate about 23...
Abstract Erosional and sedimentary features associated with flooding have been documented in both modern past cases. However, only a few studies demonstrated the relationship between these corresponding hydraulic conditions that produced them, making it difficult to evaluate magnitude of paleo-flooding. This study describes characteristics inundation depth flow direction, as well erosional resulting from disastrous Kinu River, central Japan, September 2015. Water levels rose rapidly due...
To assess long-term tsunami inundation history, we studied a wetland on the Pacific coast of Aomori, Japan, at northern end Japan Trench. We found five sand sheets interbedded in freshwater mud and peat, three which contained brackish diatoms indicating deposition by marine inundation. identified youngest sheet, deposited AD 1480–1770, as deposit based its lateral extent (>1 km) from shoreline time deposition. Although this area has been struck many tsunamis generated earthquakes along...
Abstract We examined the geochemical characteristics and temporal changes of deposits associated with 2011 Tohoku‐oki tsunami. Stable carbon isotope ratios, biomarkers, water‐leachable ions were measured in a sandy tsunami deposit soils sampled at Hasunuma, Kujukuri coastal plain, Japan, 2014. At this site, formed 10–30 cm ‐thick layer very fine to medium sand. The was organic‐poor, no samples contained any detectable biomarkers either terrigenous or marine origin. In underlying soil, we...
Abstract We describe the detailed sedimentary characteristics of a tsunami deposit associated with 2011 Tohoku‐oki in Hasunuma, site on Kujukuri coastal plain, Japan. The thick was limited to within 350 m from coastline whereas inundation area extended about 1 km coastline. sampled by excavation at 29 locations along three transects and studied using peels, soft‐X imaging grain‐size analysis. covers pre‐existing soil reached maximum measured thickness 35 cm. It consists mainly well‐sorted...
Scour ponds from unusually large tsunamis cut across the crest of a beach ridge in Kiritappu marsh, eastern Hokkaido. No fewer than ten these were imaged by photogrammetry as elongate topographic depressions 5 m 30 m. Sediments are underlain unconformities that detected with ground-penetrating radar and observed directly cores slice sample. Sediment deposits contain peat volcanic ash layers, ages which suggest scouring occurred during generated spatially extensive thrust ruptures along...
This study investigates the Holocene sedimentary history of a small coastal lowland in Nankoku, Kochi Prefecture, on coast southern Japan facing Nankai Trough. The fill area consists mainly marine-brackish clay overlain by beds freshwater and peat. We found four laterally extensive sand sheets, one directly underlying deposits other three interbedded with them. Radiocarbon dates show that these sheets were deposited between 5970 2440 cal. BP. Although contained few diatoms, they concentrated...
Stratigraphic and paleontological investigations in Mugi Town, on the Pacific coast of Shikoku Island, revealed evidence as many five tsunami inundations from events along Nankai Trough between 5581 3640 cal yr BP. Nine event deposits (E1–E9) were identified cores ranging length 2 to 6 m, consisting sandy gravelly layers interbedded with organic-rich mud. Sedimentary structures observed by computed tomography included normal grading sharp lower stratigraphic contacts. Event E3, E6, E7, E8...
東北地方北部の太平洋岸における長期間の地震・津波の履歴およびその規模を明らかにすることを目的に，青森県三沢市の低湿地において津波堆積物調査を行った．その結果，シルト層および粘土層中に挟在する2層のイベント砂層を検出した．上位のイベント砂層は人為的な擾乱によりその成因は特定できない．下位のイベント砂層は4,800〜2,900calBPに堆積したと推定され，海岸線から内陸約700mの地点から約1kmにわたって連続的に堆積し，内陸に向かって細粒化する．また，砂層中とその直上の粘土層中には淡水生珪藻だけでなく汽水生珪藻も含まれている．このイベント砂層は津波により形成された可能性もあるが，上位の地層からも汽水生珪藻が産出することから，背後の海成段丘構成層からの流れ込みによって形成された可能性も否定できない．また，周辺地域でこのイベント砂層に対比される津波堆積物の報告はなく，イベント砂層の成因を明らかにするにはさらに調査を進める必要がある．
Abstract The distributions of sandy tsunami deposits do not reflect the true extents inundation areas, leading to underestimates by past tsunamis and thus magnitudes their associated tsunamigenic earthquakes. To archive sedimentological geochemical features 2011 Tohoku-oki deposit, we performed visual observations computed tomography, grain-size, water content, organic analyses sediments from a coastal forest at Oirase Town, northern Japan. Stratigraphic revealed deposit be landward-thinning...
Abstract This paper documents the sedimentary characteristics of widespread deposits associated with 2011 Tohoku-oki tsunami on lowlands along Pacific coast Sendai and Fukushima regions, northern Japan, observed inundation depths. In eight areas region, field observation was carried out at a total 123 locations sampling 49 locations. Grain-size analysis soft X-ray imaging reveal that are usually composed sheetlike sandy beds generally show landward-thinning landward-fining trends landward...
Abstract Sediment cores collected at Lake Kogare-ike, a coastal lake on the Pacific coast of central Japan, record marine inundation history during last 3000 years. The sediments consist mainly organic mud, sand, gravel, inorganic and volcanic ash, events were recognized as 19 event deposits (E1–E19, from top to bottom) interbedded with mud. Visual observation by naked eyes X-ray computed tomography (CT) images identified 16 based quantitative qualitative changes in sand contents textures...
兵庫県円山川下流域(豊岡盆地)における沖積層層序,海水準変動および海岸線の変化を復元するために,ボーリングコア試料の地質層序データの解析と,コア堆積物試料のイオウ含有量,火山灰,珪藻化石および貝化石の分析,14C年代測定を行った.円山川下流域の沖積層は,下位から下部砂礫層(LG),下部砂泥層(LS),中部泥層(MM),上部砂層(US),最上部泥層(UM)に区分することができ,海成層と考えられる中部泥層が豊岡盆地全域にわたり分布している.鬱陵隠岐火山灰(U-Oki)が降下した約10,700 cal BPには,相対的海水準は標高約-30 mにあった.そして,縄文海進最盛期を示すと考えられる約6,800 BPには,細長い内湾が豊岡盆地の南端部に達した.しかし,日本列島で数多く報告されている完新世中期の高海面は確認されず,豊岡盆地は完新世の中頃には沈降傾向にあった可能性がある.これら本研究で得られた海面変化データに基づいて,10.7 ka, 7.9 6.8 kaにおける海岸線の位置を示した.
津波堆積物を使った南海トラフ沿岸での古地震・津波の研究は,過去6000年間にわたる津波の履歴解明に貢献してきた.それにより,100年~150年間隔で発生する"通常の"巨大地震以外に,より大きな地震が300~500年間隔で繰り返していると言う"ハイパー地震サイクル"仮説の提唱といったトピックもあった.このレビューでは,南海トラフ沿岸での津波堆積物研究について今後解決すべき2つのテーマを提案した.一つ目は,過去の地震の破壊域の正確な復元が改めて重要である.例えば,1707宝永地震以降は東海地震と南海地震がペアで存在するが,古い時代にはどちらか一方の記録しかないことが多い.歴史記録から漏れた地震がないかを地層記録から検証し地震履歴を補完することは,巨大地震の発生パターンを知るために重要である.もう一つは,古津波の規模(遡上高や遡上範囲)を定量化することである.これは"ハイパー地震サイクル"仮説の検証や,我々が備えるべき津波の規模を検討するために重要である.
静岡県西部に位置する太田川低地で，弥生時代中期後半から後期頃（100BC〜300AD）に相対的海水準の上昇があったことが明らかになった．相対的海水準の上昇は，河川改修工事の法面に現れた淡水成の泥炭層などを覆う“海成シルト層”によって認定された．この海成シルト層は最大で層厚約25cmで，干潟周辺に棲む貝類や珪藻の化石を含む．その上位には河川や湿地性のシルト層などが重なる．相対的海水準の上昇が起きた時期は，合計12個の14C年代測定値と土器片を用いた編年によって推定された．太田川低地で見られた相対的海水準上昇の原因は，1,000年スケールのローカルな地殻変動（沈降）と考えられる．
仙台平野南部に位置する熊の作遺跡の発掘現場において，貞観津波に対比される砂層が発見された．砂層は有機質泥層に挟まれ，下位の地層との境界は明瞭であった．砂層の最下部は変形していることが確認され，堆積物の荷重によるものと考えられた．また，変形している砂層基底部と砂層主部の間にはほぼ水平の泥層が認められ，これは一連の堆積イベントで流速が大きく変化したことを示していると考えられた．この砂層には，Nitzschia brevissimaなどの半乾燥環境や陸域を好むとされる珪藻種や，Navicula gregariaなどの汽水生の珪藻種が多産する．放射性炭素年代測定を行った結果，砂層の堆積年代として，貞観地震の発生年代と矛盾しない年代（西暦745～930年）が算出された．