Papers by Toshihiko Sugai
Journal of Geography (Chigaku Zasshi), 2015
Journal of Geography (Chigaku Zasshi), 2015
Journal of Geography (Chigaku Zasshi), 2014
The Kanto Plain is the tectonically active setting of the Tokyo metropolitan area. It is characte... more The Kanto Plain is the tectonically active setting of the Tokyo metropolitan area. It is characterized by widespread uplands, consisting of Pleistocene fluvial, marine sediment, tephra layers, and narrow lowlands filled with thick Holocene alluvium. This landscape owes its origin to the interaction of basin-forming movements, eustasy, erosion, and sedimentation during the Quaternary Period. Marine transgressions in marine isotope stages (MIS) 11, 9, and 5.5 repeatedly overlapped the land, producing Paleo Tokyo Bay, with its wide mouth facing the Pacific Ocean to the east. In contrast, the Holocene (MIS 1) marine transgression was limited to the river valleys incised since MIS 4, and instead of Paleo Tokyo Bay, Modern Tokyo Bay has appeared. Modern Tokyo Bay, which opens to the south, resulted from the combination of: (1) a lower sea level in MIS 1 than in MIS 5.5; (2) tectonic uplift of the Kanto Plain, especially the east side; and (3) the accumulation of fluvial sediment and tephr...
Ecology and Civil Engineering, 2012
To assess a fish habitat in a mountain stream, accurate estimation of the pool size is critical. ... more To assess a fish habitat in a mountain stream, accurate estimation of the pool size is critical. We estimated the surface area SA and relative water volume RWV of pools by using photographs and simple field surveys. The utility of this method was validated by comparing the estimates with those obtained by conventional cross-sectional survey. Twenty-four pools long axis: 1-7 m in a step-pool channel with a slope of around 20% were surveyed. Each pool was photographed using a digital camera affixed to the head of a 5-m-long staff. The deepest point of each pool was found and its depth measured. For each pool, the SA was estimated by analyzing the photograph and the RWV was estimated as the product of the SA and its maximum depth photographic method. In addition, the SA and water volume WV of the pools were estimated by cross-sectional survey using four transects, each with five depth measurement points. A nearly proportional relationship was observed between the SA estimated by the two methods and between the RWV estimated by the photographic method and the WV estimated by cross-sectional survey. The effort per pool required for implementing the photographic method in the field was less than one-third or one-fourth of that required when using cross-sectional survey. In addition, the cover area available to the fish in a pool could be accurately measured by analyzing the photographs. Therefore, our proposed photographic method is useful for assessing the size of pools inhabited by fish in steep mountain streams.
Journal of Geography (Chigaku Zasshi)
Marine and fluvial terraces in the Kanto Plain mostly formed in marine oxygen isotope stage (MIS)... more Marine and fluvial terraces in the Kanto Plain mostly formed in marine oxygen isotope stage (MIS) 5 under the concurrent influence of eustatic sea-level changes and Kanto basin-forming movements. In the central part of the plain, however, it remains unknown when and how terraces composed of the upper Pleistocene Joso and Kioroshi Formations, Shimosa Group developed. Terrace surfaces are classified by integrating geomorphic, sedimentary facies, and tephra analyses focusing on the southern Sashima and Tsukuba Uplands, including the northwestern Shimosa Upland. Terrace surfaces are classified into levels I to III. Terrace sediments distributed over levels I to II from the top in the Sashima, Tsukuba, and Shimosa Uplands are divided into two formations: Kioroshi Formation composed of beach facies and Joso Formation composed of flood plain and fluvial channel facies.Found in the Joso Formation were tuffaceous silt layer and pumiceous sand layer, including tephra grain correlated with On-Pm1 (c. 96 ka: Aoki et al., 2008) and Nk-Ma (c. 100 ka: Yamamoto, 2012) in the southern Sashima and Tsukuba Uplands, which allow fluvial terraces formed in the Central Kanto Plain after MIS 5c to be identified.
Bulletin of the Seismological Society of America, 2008
ABSTRACT Holocene activity of the Kuwana fault was reconstructed on the basis of 82 accelerator m... more ABSTRACT Holocene activity of the Kuwana fault was reconstructed on the basis of 82 accelerator mass spectrometry (AMS) C-14 dates and stepwise changes in the depositional rates of shallow marine sediments in four cores drilled to examine the regularity of the recurrence interval of ruptures of this active intraplate fault. In our model, depositional rates on the footwall and hanging wall are nearly equal during interseismic periods, but depositional rates on the footwall become markedly larger than those on the hanging wall just after vertical displacement of the fault. To detect the timing of each faulting event more precisely, we compared changes in the depositional rates in cores from both the downthrown (footwall) and uplifted (hanging-wall) sides of the fault. As a result, six probable and one possible paleoseismic events, including the last two historical earthquakes, were inferred to have occurred during the last 7000 yr on the basis of stepwise changes in the depositional rate on the two sides of the fault. The timing of the faulting events was estimated from depositional rate curves of four cores. Probable ages of seismic events were approximately 6200, 5700, 4000, 3600, and 2100 calendar years before present and A. D. 745 and 1586. The average earthquake recurrence interval on the Kuwana fault calculated from these data is about 1000 yr. The average vertical slip rate of the fault has been at least 1 mm/yr during the last 7000 yr.
Geomorphology, 2015
ABSTRACT The Holocene succession of the Kiso River delta − a sand-rich, river-dominated delta in ... more ABSTRACT The Holocene succession of the Kiso River delta − a sand-rich, river-dominated delta in central Japan − was analyzed at high temporal and spatial resolution. The results demonstrate how the spatiotemporal distribution of sedimentary facies, gross sediment accumulation rates, and accumulation rates of mud versus sand relate to the geomorphic development of the delta and the post-glacial, sea-level history. The centers of peak mud and sand accumulation have migrated seaward in parallel during a regressive stage from 6.5 ka to the present at a rate of 3 − 9 m/y. The mud and sand accumulation centers mark the bottom and top, respectively, of the delta-front slope. The sediments of the prograding delta show strong sorting and clear upward coarsening because of the steep slope of the delta front. Such internal topographic control redistributes and separates the coarse and fine fractions of the fluvial input during regression. The topographic-controlled sedimentary segregation constructs delta-front topography, in reverse. Therefore, the proportion of sand to mud in the fluvial input controls the stability of delta-front morphology. Our modeling of the Kiso River delta may have implications for prediction of coastal flooding adjacent to deltas in other parts of the world.
Journal of Geography (Chigaku Zasshi), 2015
Geographical Review of Japan, 2005
Geomorphologie Relief Processus Environnement, Sep 1, 2007
ABSTRACT
Geographical review of Japan series B
ABSTRACT
Chirigaku Hyoron/Geographical Review of Japan
Advances in Natural and Technological Hazards Research, 2016
The Quaternary Research (Daiyonki-Kenkyu)
To reveal the recurrence intervals of large earthquakes and fault interaction between the 1999 17... more To reveal the recurrence intervals of large earthquakes and fault interaction between the 1999 17 August Izmit (Mw 7.4) and 12 November Duzce (Mw 7.2) rupture zones, we have intensively performed trench excavation studies during the recent few years. At the center of the Izmit rupture (Tepetarla segment) we found the evidence for at least three or possibly four surface-rupturing
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Papers by Toshihiko Sugai