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Yuki Sawai - One of the best experts on this subject based on the ideXlab platform.
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Diatom assemblages within Tsunami Deposit from the 2011 Tohoku-oki earthquake along the Misawa coast, Aomori Prefecture, northern Japan
Marine Geology, 2018Co-Authors: Koichiro Tanigawa, Yuki Sawai, Yuichi NamegayaAbstract:Abstract This paper reports variations in the diatom assemblages within the Deposit from the 2011 Tohoku-oki Tsunami along the Misawa coast, Aomori Prefecture, northern Japan. The landward extent of the Tsunami Deposit was as much as 400 m inland. The Deposit contained mixed assemblages of marine-brackish and freshwater diatoms. The mixed assemblages indicated that the Tsunami Deposit was composed of not only beach and dune sand but also soil from the coastal forest. Marine-brackish species were predominant in the seaward Tsunami Deposit. However, the relative abundance of marine-brackish species rapidly decreased in the samples about 150 to 250 m inland from the shoreline. A decrease in marine-brackish diatoms at inland locations suggests that the eroded terrestrial soil was incorporated into the Tsunami Deposit. The composition of marine-brackish species in the Tsunami Deposit was different from that of modern inter- to supra- tidal sediments. One possible interpretation for this discrepancy is that the 2011 Tsunami Deposit were sourced from multiple environments, including supra-, inter- and sub- tidal locations.
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Tsunami Deposit associated with the 2011 Tohoku‐oki Tsunami in the Hasunuma site of the Kujukuri coastal plain, Japan
Island Arc, 2016Co-Authors: Dan Matsumoto, Yuki Sawai, Masanobu Shishikura, Koichiro Tanigawa, Yuichi Namegaya, Osamu Fujiwara, Kyoko Kagohara, Haruo KimuraAbstract:We describe the detailed sedimentary characteristics of a Tsunami Deposit associated with the 2011 Tohoku-oki Tsunami in Hasunuma, a site on the Kujukuri coastal plain, Japan. The thick Tsunami Deposit was limited to within 350 m from the coastline whereas the inundation area extended about 1 km from the coastline. The Tsunami Deposit was sampled by excavation at 29 locations along three transects and studied using peels, soft-X imaging and grain-size analysis. The Deposit covers the pre-existing soil and reached a maximum measured thickness of 35 cm. It consists mainly of well-sorted medium to fine sand. On the basis of sedimentary structures and changes in grain size, we divided the Tsunami Deposit into several sedimentary units, which may correspond to multiple inundation flows. The numbers of units and their sedimentary features vary among the three transects, despite the similar topography. This variation implies a considerable influence of local effects such as elevation, vegetation, microtopography, and distance from footpaths, on the Tsunami-related sedimentation.
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Tsunami Deposit associated with the 2011 tohoku oki Tsunami in the hasunuma site of the kujukuri coastal plain japan
Island Arc, 2016Co-Authors: Dan Matsumoto, Yuki Sawai, Masanobu Shishikura, Koichiro Tanigawa, Yuichi Namegaya, Osamu Fujiwara, Kyoko Kagohara, Haruo KimuraAbstract:We describe the detailed sedimentary characteristics of a Tsunami Deposit associated with the 2011 Tohoku-oki Tsunami in Hasunuma, a site on the Kujukuri coastal plain, Japan. The thick Tsunami Deposit was limited to within 350 m from the coastline whereas the inundation area extended about 1 km from the coastline. The Tsunami Deposit was sampled by excavation at 29 locations along three transects and studied using peels, soft-X imaging and grain-size analysis. The Deposit covers the pre-existing soil and reached a maximum measured thickness of 35 cm. It consists mainly of well-sorted medium to fine sand. On the basis of sedimentary structures and changes in grain size, we divided the Tsunami Deposit into several sedimentary units, which may correspond to multiple inundation flows. The numbers of units and their sedimentary features vary among the three transects, despite the similar topography. This variation implies a considerable influence of local effects such as elevation, vegetation, microtopography, and distance from footpaths, on the Tsunami-related sedimentation.
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OSL dating of the AD 869 Jogan Tsunami Deposit, northeastern Japan
Quaternary Geochronology, 2015Co-Authors: Toru Tamura, Yuki Sawai, Kazumi ItoAbstract:Sediments Deposited by the AD 869 Jogan Tsunami offer an opportunity to test the reliability of optically stimulated luminescence (OSL) dating of relatively old historical Tsunami Deposits. We collected a geoslicer sample from sand Deposited on the Sendai Plain, northeastern Japan, by the Jogan Tsunami and applied quartz OSL dating to it. We then compared the OSL ages with the known age of the Tsunami event. In ascending order, the sedimentary sequence in the geoslicer sample consists of the beach–dune sand, lower peat, Jogan Tsunami Deposit, upper peat, pre-2011 paddy soil, and the 2011 Tsunami Deposit. To obtain equivalent dose (De,bulk), a standard single-aliquot renegerative-dose (SAR) protocol was applied to large aliquots of the 180–250 μm fraction of two samples from the beach–dune sand, and four samples from differing levels of the Jogan Tsunami Deposit. The OSL decay curves were dominated by the medium component; thus, for two samples from the Jogan Deposit the fast-component OSL signal was isolated and used to determine the equivalent dose (De,fast). Using De,bulk, OSL ages of the Tsunami Deposit were underestimated by ∼40%, and even the beach–dune sand was dated younger than AD 869. In contrast, De,fast provided a robust age estimate with only slight underestimation. A pulse annealing test showed that the bulk and medium-component OSL signals were thermally unstable. The medium component in the natural OSL was clearly truncated in comparison to the regenerated OSL; the medium component is thus considered to be the main cause of the underestimated ages. Similar effects of a dominant medium-component OSL have been reported in tectonically active regions, which are also prone to Tsunamis. The effect of this dominance should be carefully considered in quartz OSL dating of Tsunami Deposits.
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microfossils from coastal environments as indicators of paleo earthquakes Tsunamis and storms
Palaeogeography Palaeoclimatology Palaeoecology, 2014Co-Authors: Benjamin P Horton, Jessica E Pilarczyk, Tina Dura, Simon E Engelhart, Andrew C Kemp, Yuki SawaiAbstract:Abstract Coastal risk assessment and hazard mitigation require datasets on centennial and millennial temporal scales to capture natural variability and multiple occurrences of the largest, but least frequent, events. Coastal sediments from low-energy Depositional environments archive geologic evidence of paleo-earthquakes, Tsunamis, and storms. Many of the best reconstructions of these events are derived from changes in microfossil (diatoms, foraminifera, and pollen) assemblages. In this review we explain how microfossils are used to reconstruct records of paleoearthquakes by quantifying the amount of coseismic and interseismic vertical land movements along tectonically active coastlines. Examples from the United States (Alaska and the Pacific Northwest), Japan, and Chile show that microfossil-based transfer functions may provide continuous records of vertical land movement during earthquake deformation cycles. We discuss how microfossil habitat preferences and taphonomic character are used to constrain sediment provenance (e.g., beach, nearshore, or offshore sources) and identify overwash Deposits, and how this information can be used to reconstruct the recurrence of Tsunamis and storms. Analysis of overwash Deposits from Thailand and Malaysia indicates the ability of microfossils to resolve individual waves within Tsunami sediments, and an example from the Sendai coastal plain in Japan uses foraminifera to ascribe a beach to nearshore provenance for the 2011 Tohoku Tsunami Deposit. Finally, we present recent examples from the Gulf of Mexico on the use of foraminifera to estimate the volume and distance of transport of storm overwash from hurricanes.
Kenji Satake - One of the best experts on this subject based on the ideXlab platform.
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effects of topography on particle composition of 2011 Tsunami Deposits on the ria type sanriku coast japan
Quaternary International, 2017Co-Authors: Tomoko Goto, Kenji Satake, Toshihiko Sugai, Takeo Ishibe, Tomoya Harada, Aditya Riadi GusmanAbstract:Abstract A geological survey was conducted in a small valley along the Sanriku coast, and the grain compositions of both autochthonous gravels and the 2011 Tsunami Deposit from the Tohoku-oki earthquake were investigated to reveal the Depositional form of the Tsunami Deposits on the ria-type coast. The features of autochthonous gravels in the beach, riverbed, and slope areas are characterized by a combination of their rock type and roundness. The roundness values of the beach and slope gravels are large (0.8–0.9) and small (0.1–0.2), respectively, regardless of rock type, and the riverbed gravels are typically granite rocks with an intermediate roundness (0.4–0.5). The 2011 Tsunami Deposits along the survey transect include the above autochthonous gravels and show several characteristic features, such as a sharp erosional contact with the underlying peaty soil, normal and/or inverse grading structures, mud sheets, and richness in gravels in the lower unit, while the thickness shows no systematic changes with the distance from the coast. The presence of slope gravels suggests high Tsunami inundation and flux, which eroded bare rock and talus and transported them to the valley plain by backwash current. The mixture of beach and riverbed Deposits implies the formation of both an upstream current from the beach, which transported beach pebbles inland, and a backwash current along the channel, which accumulated sub-angular riverbed gravels around the river mouth. The characteristics of the 2011 Tsunami Deposit on the Sanriku coast, where narrow valleys are surrounded by high cliffs with steep slopes, are significantly different from those of sandy Tsunami Deposits in Sendai Plain, where a flat plain develops within several kilometers of the coastline. The differences among sedimentary facies are affected by the topography and autochthonous Deposits.
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reexamination of the a d 869 jogan earthquake size from Tsunami Deposit distribution simulated flow depth and velocity
Geophysical Research Letters, 2014Co-Authors: Yuichi Namegaya, Kenji SatakeAbstract:The rupture parameters and magnitude of the A.D. 869 Jogan earthquake, a predecessor of the 2011 Tohoku earthquake, were previously estimated by matching Tsunami Deposit distributions with simulated inundation areas. The Tsunami inundation associated with the 2011 Tohoku earthquake, however, extended farther inland than the sandy Tsunami Deposits. Numerical simulation of the 2011 Tsunami indicated that flow depths and velocities were approximately 1 m and 0.6 m/s, respectively, at the most inland sand Deposit sites on the Ishinomaki and Sendai plains. While these values depend on the assumed bottom roughness, we used these values to compare Tsunami Deposits and inundation simulation of the 869 Jogan earthquake from both uniform-slip and 2011-type variable-slip fault models. The results showed that the rupture length of the 869 Jogan earthquake was at least 200 km and its minimum moment magnitude was 8.6.
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challenges of anticipating the 2011 tohoku earthquake and Tsunami using coastal geology
Geophysical Research Letters, 2012Co-Authors: Yuki Sawai, Kenji Satake, Yukinobu Okamura, Yuichi Namegaya, Masanobu ShishikuraAbstract:[1] Can the magnitude of a giant earthquake be estimated from paleoseismological data alone? Attempts to estimate the size of the Jogan earthquake of AD 869, whose Tsunami affected much of the same coast as the 2011 Tohoku Tsunami, offers an excellent opportunity to address this question, which is fundamental to assessing earthquake and Tsunami hazards at subduction zones. Between 2004 and 2010, examining stratigraphy at 399 locations beneath paddy fields along 180 km of coast mainly south of Sendai, we learned that a Tsunami Deposit associated with the AD 869 Jogan earthquake had run inland at least 1.5 km across multiple coastal lowlands, and that one of the lowlands had subsided during the Jogan earthquake and an earlier earthquake as well. Radiocarbon ages just below/above sand Deposits left by the pre-Jogan Tsunamis suggested recurrence intervals in the range of 500 to 800 years. Modeling inundation and subsidence, we estimated size of the Jogan earthquake as moment magnitude 8.4 or larger and a fault rupture area 200 km long. We did not consider a longer rupture, like the one in 2011, because coastal landform and absence of a volcanic ash layer make any Jogan layer difficult to identify along the Sanriku coast. Still, Sendai Tsunami geology might have reduced casualties by improving evacuation maps and informing public-awareness campaigns.
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aperiodic recurrence of geologically recorded Tsunamis during the past 5500 years in eastern hokkaido japan
Journal of Geophysical Research, 2009Co-Authors: Yuki Sawai, Kenji Satake, Takanobu Kamataki, Masanobu Shishikura, Hiroo Nasu, Yukinobu Okamura, Katie Thomson, Dan Matsumoto, Yushiro FujiiAbstract:[1] Along Hokkaido's Pacific coast near the town of Kiritappu, sandy Deposits in a muddy lagoon and on a nearby beach-ridge plain provide evidence for 15 Tsunamis between 200 and 6000 years ago. Additional sand beds at the lagoon probably represent the historical Tsunamis of A.D. 1843 and 1894. We observed the sequences of sandy Deposits in continuous slices 2 to 4 m deep. Some of the Deposits consist of just a single sand bed, whereas others contain multiple units of sand, muddy sand (or sandy mud), and mud caps including plant detritus. We also found at the lagoon a 17th century Tsunami Deposit that thickens and thins regardless of elevation or distance inland. We bracketed the ages of most of the inferred Tsunamis by radiocarbon dating of detritus, mainly seeds and leaves at the lagoon and charcoal at the beach-ridge plain, from preTsunami and postTsunami beds. Tsunami dates computed from the bracketing ages commonly have uncertainties spanning 2 to 4 centuries. Within these uncertainties, the inferred sequence of 15 prehistoric Tsunamis at the lagoon, beginning almost 6000 years ago, can be matched Tsunami by Tsunami with the inferred history at the beach-ridge plain, 15 km away. The sand sheet extents suggest that most of these Tsunamis were larger than any generated at Hokkaido in the last 200 years. The intervals between these inferred outsized Tsunamis average nearly 400 years but range widely from about 100 to about 800 years.
Yuichi Namegaya - One of the best experts on this subject based on the ideXlab platform.
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Diatom assemblages within Tsunami Deposit from the 2011 Tohoku-oki earthquake along the Misawa coast, Aomori Prefecture, northern Japan
Marine Geology, 2018Co-Authors: Koichiro Tanigawa, Yuki Sawai, Yuichi NamegayaAbstract:Abstract This paper reports variations in the diatom assemblages within the Deposit from the 2011 Tohoku-oki Tsunami along the Misawa coast, Aomori Prefecture, northern Japan. The landward extent of the Tsunami Deposit was as much as 400 m inland. The Deposit contained mixed assemblages of marine-brackish and freshwater diatoms. The mixed assemblages indicated that the Tsunami Deposit was composed of not only beach and dune sand but also soil from the coastal forest. Marine-brackish species were predominant in the seaward Tsunami Deposit. However, the relative abundance of marine-brackish species rapidly decreased in the samples about 150 to 250 m inland from the shoreline. A decrease in marine-brackish diatoms at inland locations suggests that the eroded terrestrial soil was incorporated into the Tsunami Deposit. The composition of marine-brackish species in the Tsunami Deposit was different from that of modern inter- to supra- tidal sediments. One possible interpretation for this discrepancy is that the 2011 Tsunami Deposit were sourced from multiple environments, including supra-, inter- and sub- tidal locations.
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Tsunami Deposit associated with the 2011 Tohoku‐oki Tsunami in the Hasunuma site of the Kujukuri coastal plain, Japan
Island Arc, 2016Co-Authors: Dan Matsumoto, Yuki Sawai, Masanobu Shishikura, Koichiro Tanigawa, Yuichi Namegaya, Osamu Fujiwara, Kyoko Kagohara, Haruo KimuraAbstract:We describe the detailed sedimentary characteristics of a Tsunami Deposit associated with the 2011 Tohoku-oki Tsunami in Hasunuma, a site on the Kujukuri coastal plain, Japan. The thick Tsunami Deposit was limited to within 350 m from the coastline whereas the inundation area extended about 1 km from the coastline. The Tsunami Deposit was sampled by excavation at 29 locations along three transects and studied using peels, soft-X imaging and grain-size analysis. The Deposit covers the pre-existing soil and reached a maximum measured thickness of 35 cm. It consists mainly of well-sorted medium to fine sand. On the basis of sedimentary structures and changes in grain size, we divided the Tsunami Deposit into several sedimentary units, which may correspond to multiple inundation flows. The numbers of units and their sedimentary features vary among the three transects, despite the similar topography. This variation implies a considerable influence of local effects such as elevation, vegetation, microtopography, and distance from footpaths, on the Tsunami-related sedimentation.
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Tsunami Deposit associated with the 2011 tohoku oki Tsunami in the hasunuma site of the kujukuri coastal plain japan
Island Arc, 2016Co-Authors: Dan Matsumoto, Yuki Sawai, Masanobu Shishikura, Koichiro Tanigawa, Yuichi Namegaya, Osamu Fujiwara, Kyoko Kagohara, Haruo KimuraAbstract:We describe the detailed sedimentary characteristics of a Tsunami Deposit associated with the 2011 Tohoku-oki Tsunami in Hasunuma, a site on the Kujukuri coastal plain, Japan. The thick Tsunami Deposit was limited to within 350 m from the coastline whereas the inundation area extended about 1 km from the coastline. The Tsunami Deposit was sampled by excavation at 29 locations along three transects and studied using peels, soft-X imaging and grain-size analysis. The Deposit covers the pre-existing soil and reached a maximum measured thickness of 35 cm. It consists mainly of well-sorted medium to fine sand. On the basis of sedimentary structures and changes in grain size, we divided the Tsunami Deposit into several sedimentary units, which may correspond to multiple inundation flows. The numbers of units and their sedimentary features vary among the three transects, despite the similar topography. This variation implies a considerable influence of local effects such as elevation, vegetation, microtopography, and distance from footpaths, on the Tsunami-related sedimentation.
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reexamination of the a d 869 jogan earthquake size from Tsunami Deposit distribution simulated flow depth and velocity
Geophysical Research Letters, 2014Co-Authors: Yuichi Namegaya, Kenji SatakeAbstract:The rupture parameters and magnitude of the A.D. 869 Jogan earthquake, a predecessor of the 2011 Tohoku earthquake, were previously estimated by matching Tsunami Deposit distributions with simulated inundation areas. The Tsunami inundation associated with the 2011 Tohoku earthquake, however, extended farther inland than the sandy Tsunami Deposits. Numerical simulation of the 2011 Tsunami indicated that flow depths and velocities were approximately 1 m and 0.6 m/s, respectively, at the most inland sand Deposit sites on the Ishinomaki and Sendai plains. While these values depend on the assumed bottom roughness, we used these values to compare Tsunami Deposits and inundation simulation of the 869 Jogan earthquake from both uniform-slip and 2011-type variable-slip fault models. The results showed that the rupture length of the 869 Jogan earthquake was at least 200 km and its minimum moment magnitude was 8.6.
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challenges of anticipating the 2011 tohoku earthquake and Tsunami using coastal geology
Geophysical Research Letters, 2012Co-Authors: Yuki Sawai, Kenji Satake, Yukinobu Okamura, Yuichi Namegaya, Masanobu ShishikuraAbstract:[1] Can the magnitude of a giant earthquake be estimated from paleoseismological data alone? Attempts to estimate the size of the Jogan earthquake of AD 869, whose Tsunami affected much of the same coast as the 2011 Tohoku Tsunami, offers an excellent opportunity to address this question, which is fundamental to assessing earthquake and Tsunami hazards at subduction zones. Between 2004 and 2010, examining stratigraphy at 399 locations beneath paddy fields along 180 km of coast mainly south of Sendai, we learned that a Tsunami Deposit associated with the AD 869 Jogan earthquake had run inland at least 1.5 km across multiple coastal lowlands, and that one of the lowlands had subsided during the Jogan earthquake and an earlier earthquake as well. Radiocarbon ages just below/above sand Deposits left by the pre-Jogan Tsunamis suggested recurrence intervals in the range of 500 to 800 years. Modeling inundation and subsidence, we estimated size of the Jogan earthquake as moment magnitude 8.4 or larger and a fault rupture area 200 km long. We did not consider a longer rupture, like the one in 2011, because coastal landform and absence of a volcanic ash layer make any Jogan layer difficult to identify along the Sanriku coast. Still, Sendai Tsunami geology might have reduced casualties by improving evacuation maps and informing public-awareness campaigns.
Masanobu Shishikura - One of the best experts on this subject based on the ideXlab platform.
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Tsunami Deposit associated with the 2011 Tohoku‐oki Tsunami in the Hasunuma site of the Kujukuri coastal plain, Japan
Island Arc, 2016Co-Authors: Dan Matsumoto, Yuki Sawai, Masanobu Shishikura, Koichiro Tanigawa, Yuichi Namegaya, Osamu Fujiwara, Kyoko Kagohara, Haruo KimuraAbstract:We describe the detailed sedimentary characteristics of a Tsunami Deposit associated with the 2011 Tohoku-oki Tsunami in Hasunuma, a site on the Kujukuri coastal plain, Japan. The thick Tsunami Deposit was limited to within 350 m from the coastline whereas the inundation area extended about 1 km from the coastline. The Tsunami Deposit was sampled by excavation at 29 locations along three transects and studied using peels, soft-X imaging and grain-size analysis. The Deposit covers the pre-existing soil and reached a maximum measured thickness of 35 cm. It consists mainly of well-sorted medium to fine sand. On the basis of sedimentary structures and changes in grain size, we divided the Tsunami Deposit into several sedimentary units, which may correspond to multiple inundation flows. The numbers of units and their sedimentary features vary among the three transects, despite the similar topography. This variation implies a considerable influence of local effects such as elevation, vegetation, microtopography, and distance from footpaths, on the Tsunami-related sedimentation.
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Tsunami Deposit associated with the 2011 tohoku oki Tsunami in the hasunuma site of the kujukuri coastal plain japan
Island Arc, 2016Co-Authors: Dan Matsumoto, Yuki Sawai, Masanobu Shishikura, Koichiro Tanigawa, Yuichi Namegaya, Osamu Fujiwara, Kyoko Kagohara, Haruo KimuraAbstract:We describe the detailed sedimentary characteristics of a Tsunami Deposit associated with the 2011 Tohoku-oki Tsunami in Hasunuma, a site on the Kujukuri coastal plain, Japan. The thick Tsunami Deposit was limited to within 350 m from the coastline whereas the inundation area extended about 1 km from the coastline. The Tsunami Deposit was sampled by excavation at 29 locations along three transects and studied using peels, soft-X imaging and grain-size analysis. The Deposit covers the pre-existing soil and reached a maximum measured thickness of 35 cm. It consists mainly of well-sorted medium to fine sand. On the basis of sedimentary structures and changes in grain size, we divided the Tsunami Deposit into several sedimentary units, which may correspond to multiple inundation flows. The numbers of units and their sedimentary features vary among the three transects, despite the similar topography. This variation implies a considerable influence of local effects such as elevation, vegetation, microtopography, and distance from footpaths, on the Tsunami-related sedimentation.
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challenges of anticipating the 2011 tohoku earthquake and Tsunami using coastal geology
Geophysical Research Letters, 2012Co-Authors: Yuki Sawai, Kenji Satake, Yukinobu Okamura, Yuichi Namegaya, Masanobu ShishikuraAbstract:[1] Can the magnitude of a giant earthquake be estimated from paleoseismological data alone? Attempts to estimate the size of the Jogan earthquake of AD 869, whose Tsunami affected much of the same coast as the 2011 Tohoku Tsunami, offers an excellent opportunity to address this question, which is fundamental to assessing earthquake and Tsunami hazards at subduction zones. Between 2004 and 2010, examining stratigraphy at 399 locations beneath paddy fields along 180 km of coast mainly south of Sendai, we learned that a Tsunami Deposit associated with the AD 869 Jogan earthquake had run inland at least 1.5 km across multiple coastal lowlands, and that one of the lowlands had subsided during the Jogan earthquake and an earlier earthquake as well. Radiocarbon ages just below/above sand Deposits left by the pre-Jogan Tsunamis suggested recurrence intervals in the range of 500 to 800 years. Modeling inundation and subsidence, we estimated size of the Jogan earthquake as moment magnitude 8.4 or larger and a fault rupture area 200 km long. We did not consider a longer rupture, like the one in 2011, because coastal landform and absence of a volcanic ash layer make any Jogan layer difficult to identify along the Sanriku coast. Still, Sendai Tsunami geology might have reduced casualties by improving evacuation maps and informing public-awareness campaigns.
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aperiodic recurrence of geologically recorded Tsunamis during the past 5500 years in eastern hokkaido japan
Journal of Geophysical Research, 2009Co-Authors: Yuki Sawai, Kenji Satake, Takanobu Kamataki, Masanobu Shishikura, Hiroo Nasu, Yukinobu Okamura, Katie Thomson, Dan Matsumoto, Yushiro FujiiAbstract:[1] Along Hokkaido's Pacific coast near the town of Kiritappu, sandy Deposits in a muddy lagoon and on a nearby beach-ridge plain provide evidence for 15 Tsunamis between 200 and 6000 years ago. Additional sand beds at the lagoon probably represent the historical Tsunamis of A.D. 1843 and 1894. We observed the sequences of sandy Deposits in continuous slices 2 to 4 m deep. Some of the Deposits consist of just a single sand bed, whereas others contain multiple units of sand, muddy sand (or sandy mud), and mud caps including plant detritus. We also found at the lagoon a 17th century Tsunami Deposit that thickens and thins regardless of elevation or distance inland. We bracketed the ages of most of the inferred Tsunamis by radiocarbon dating of detritus, mainly seeds and leaves at the lagoon and charcoal at the beach-ridge plain, from preTsunami and postTsunami beds. Tsunami dates computed from the bracketing ages commonly have uncertainties spanning 2 to 4 centuries. Within these uncertainties, the inferred sequence of 15 prehistoric Tsunamis at the lagoon, beginning almost 6000 years ago, can be matched Tsunami by Tsunami with the inferred history at the beach-ridge plain, 15 km away. The sand sheet extents suggest that most of these Tsunamis were larger than any generated at Hokkaido in the last 200 years. The intervals between these inferred outsized Tsunamis average nearly 400 years but range widely from about 100 to about 800 years.
Dan Matsumoto - One of the best experts on this subject based on the ideXlab platform.
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Tsunami Deposit associated with the 2011 Tohoku‐oki Tsunami in the Hasunuma site of the Kujukuri coastal plain, Japan
Island Arc, 2016Co-Authors: Dan Matsumoto, Yuki Sawai, Masanobu Shishikura, Koichiro Tanigawa, Yuichi Namegaya, Osamu Fujiwara, Kyoko Kagohara, Haruo KimuraAbstract:We describe the detailed sedimentary characteristics of a Tsunami Deposit associated with the 2011 Tohoku-oki Tsunami in Hasunuma, a site on the Kujukuri coastal plain, Japan. The thick Tsunami Deposit was limited to within 350 m from the coastline whereas the inundation area extended about 1 km from the coastline. The Tsunami Deposit was sampled by excavation at 29 locations along three transects and studied using peels, soft-X imaging and grain-size analysis. The Deposit covers the pre-existing soil and reached a maximum measured thickness of 35 cm. It consists mainly of well-sorted medium to fine sand. On the basis of sedimentary structures and changes in grain size, we divided the Tsunami Deposit into several sedimentary units, which may correspond to multiple inundation flows. The numbers of units and their sedimentary features vary among the three transects, despite the similar topography. This variation implies a considerable influence of local effects such as elevation, vegetation, microtopography, and distance from footpaths, on the Tsunami-related sedimentation.
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Tsunami Deposit associated with the 2011 tohoku oki Tsunami in the hasunuma site of the kujukuri coastal plain japan
Island Arc, 2016Co-Authors: Dan Matsumoto, Yuki Sawai, Masanobu Shishikura, Koichiro Tanigawa, Yuichi Namegaya, Osamu Fujiwara, Kyoko Kagohara, Haruo KimuraAbstract:We describe the detailed sedimentary characteristics of a Tsunami Deposit associated with the 2011 Tohoku-oki Tsunami in Hasunuma, a site on the Kujukuri coastal plain, Japan. The thick Tsunami Deposit was limited to within 350 m from the coastline whereas the inundation area extended about 1 km from the coastline. The Tsunami Deposit was sampled by excavation at 29 locations along three transects and studied using peels, soft-X imaging and grain-size analysis. The Deposit covers the pre-existing soil and reached a maximum measured thickness of 35 cm. It consists mainly of well-sorted medium to fine sand. On the basis of sedimentary structures and changes in grain size, we divided the Tsunami Deposit into several sedimentary units, which may correspond to multiple inundation flows. The numbers of units and their sedimentary features vary among the three transects, despite the similar topography. This variation implies a considerable influence of local effects such as elevation, vegetation, microtopography, and distance from footpaths, on the Tsunami-related sedimentation.
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Sedimentary features observed in the Tsunami Deposits at Rikuzentakata City
Sedimentary Geology, 2012Co-Authors: Hajime Naruse, Dan Matsumoto, Kazuno Arai, Hiroki Takahashi, Shota Yamashita, Gengo Tanaka, Masafumi MurayamaAbstract:Abstract The March 11, 2011 Tohoku-Oki Tsunami triggered by an earthquake off the east coast of northeastern Honshu Island (Tohoku region), Japan, Deposited large amounts of sediment on land, including the Sendai Plain and Sanriku Coast. This study reports on the characteristics of the Tsunami Deposits in Rikuzentakata City, southeastern Iwate Prefecture, northeastern Japan. A field survey identified the inundation pattern of the Tsunami in this region and the facies model of the Tsunami Deposits at the bay-head deltas of estuarine systems. The Tsunami Deposits in Rikuzentakata City generally consist of one to four units that represent a discrete runup or backwash flow. Each unit is characterized by initial inverse grading and successive normal grading that correspond to the accelerating and decelerating stages of the flow, respectively. An internal erosional surface often developed between the inverse-graded and normal-graded units. It corresponds to the maximum shear velocity of the flow and truncates the underlying inverse-graded unit. In the case of the runup unit, silty fine-grained drapes overlay the graded sandy interval. A correlation of the sedimentary structures and grain fabric analysis revealed that the Tohoku-Oki Tsunami inundated Rikuzentakata City at least twice and that the flow velocity exceeded 2.4 m/s. Paleontological analysis of the sediment and kriging estimation of the total volume of the Tsunami Deposit implied that the sediments were sourced not only from eroded beach sands but also from the seafloor of Hirota Bay or more offshore regions.
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detailed measurements of thickness and grain size of a widespread onshore Tsunami Deposit in phang nga province southwestern thailand
Island Arc, 2010Co-Authors: Shigehiro Fujino, Dan Matsumoto, Hajime Naruse, Norihiko Sakakura, Apichart Suphawajruksakul, Thanawat JarupongsakulAbstract:Measurements of thickness and grain size along flow-parallel transects across onshore Deposits of the 2004 Indian Ocean Tsunami revealed macroscopic horizontal variations and provided new insights into Tsunami sedimentation. The Tsunami caused severe erosion of beaches, river mouths, and the shallow seafloor along the coast of southwestern Thailand and supplied sufficient sediment to Deposit a kilometer-wide blanket of sand on the land surface. The Tsunami Deposits generally fine landward with some fluctuations caused by local entrainment and settlement of sediments. Sediments of medium and fine sand are restricted to a few hundreds of meters inland from their source, whereas finer grained sediments were suspended longer and Deposited 1 km or more inland. Although the thickness of the Tsunami Deposits is strongly influenced by local topography, they generally thin landward. In areas of low-relief topography, the rate of landward thinning is exponential and reflects the dominance of sediment supply to nearshore areas over that to areas farther inland.
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aperiodic recurrence of geologically recorded Tsunamis during the past 5500 years in eastern hokkaido japan
Journal of Geophysical Research, 2009Co-Authors: Yuki Sawai, Kenji Satake, Takanobu Kamataki, Masanobu Shishikura, Hiroo Nasu, Yukinobu Okamura, Katie Thomson, Dan Matsumoto, Yushiro FujiiAbstract:[1] Along Hokkaido's Pacific coast near the town of Kiritappu, sandy Deposits in a muddy lagoon and on a nearby beach-ridge plain provide evidence for 15 Tsunamis between 200 and 6000 years ago. Additional sand beds at the lagoon probably represent the historical Tsunamis of A.D. 1843 and 1894. We observed the sequences of sandy Deposits in continuous slices 2 to 4 m deep. Some of the Deposits consist of just a single sand bed, whereas others contain multiple units of sand, muddy sand (or sandy mud), and mud caps including plant detritus. We also found at the lagoon a 17th century Tsunami Deposit that thickens and thins regardless of elevation or distance inland. We bracketed the ages of most of the inferred Tsunamis by radiocarbon dating of detritus, mainly seeds and leaves at the lagoon and charcoal at the beach-ridge plain, from preTsunami and postTsunami beds. Tsunami dates computed from the bracketing ages commonly have uncertainties spanning 2 to 4 centuries. Within these uncertainties, the inferred sequence of 15 prehistoric Tsunamis at the lagoon, beginning almost 6000 years ago, can be matched Tsunami by Tsunami with the inferred history at the beach-ridge plain, 15 km away. The sand sheet extents suggest that most of these Tsunamis were larger than any generated at Hokkaido in the last 200 years. The intervals between these inferred outsized Tsunamis average nearly 400 years but range widely from about 100 to about 800 years.
