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Ishii, Eiichi; Furusawa, Akira*
Engineering Geology, 228, p.158 - 166, 2017/10
Times Cited Count：6 Percentile：31.36(Engineering, Geological)We present detailed mineralogical and geochemical analyses of clay-rich shear zones that are associated with bedding-parallel or bedding-oblique faults in drill cores of a siliceous mudstone from the Horonobe area, northern Hokkaido, Japan. The bedding-parallel shear zones are rich in smectite and some shear zones are characterized by melt inclusions hosted by plagioclase and quartz. The chemical compositions of melt inclusions in six shear zones are very similar, but distinct from those of melt inclusions in other shear zones. These six shear zones consistently occur in horizons 
350 m shallower than a known tephra layer. These mineralogical characteristics and stratigraphic positions suggest that the six shear zones occur within the same tephra layer and that the smectite formed as a result of burial diagenesis of volcanic glass. Tephra-derived smectite-rich shear zones can be detected and correlated by analyzing melt inclusions preserved in mineral grains.
Yasue, Kenichi; Takatori, Ryoichi*; Tanikawa, Shinichi*; Ninomiya, Atsushi*; Tanase, Atsushi*; Furusawa, Akira*; Tajikara, Masayoshi*
Chishitsugaku Zasshi, 120(12), p.435 - 445, 2014/12
Estimating the rate of change in landforms and geological environments due to erosion is important when assessing the safety of the geological disposal of high-level radioactive waste in Japan. The aim of this study is to develop an index of erosion rates in inland mountains. We focused on circular abandoned channels, which are old river valleys around detached meander cores formed by the cut-off of incised meandering rivers. The channels can be useful for estimating incision rates because they occur at a range of elevations throughout the Japanese Islands. We undertook a case study to determine the incision rate using a circular abandoned channel in the middle reaches of the Kumanogawa River in the Kii Peninsula, where many circular abandoned channels have been identified. We obtained undisturbed core samples of old river channel deposits and angular gravel deposits that overlie the circular abandoned channel. The old river channel deposits have been emergent since at least MIS5, based on an analysis of the soil color in angular gravel deposits. The incision rate, as calculated from this age and the difference in elevation between the abandoned and present channels, is less than about 0.9 m/ky. This study shows that analyses of circular abandoned channels can yield estimates of incision rates and potentially also uplift rates. More accurate estimates of incision rates require further studies of the dating and evolution of sediments that overlie circular abandoned channels.
Furusawa, Akira*; Yasue, Kenichi; Nakamura, Chisato*; Umeda, Koji
Oyo Chishitsu, 54(1), p.25 - 38, 2013/04
Distinguishing strongly weathered tephras is very difficult because major-element chemistry of volcanic glasses is affected by weathering. On the other hand, it recently became clear that major-element analysis of glass inclusions in quartz and plagioclase is an effective method of investigating strongly weathered tephras. We studied the weathered tephras in the Toki Sand and Gravel Formation (TSG) located on the Nenoue highland, in the hanging wall of the Byobuyama fault. The TSG consists mainly of gravel beds with intercalated clay-sand beds in the lower and middle horizons. Glass inclusions in the quartz occur only in the weathered clay-sand beds. We found that the glass inclusions in the quartz in the middle horizons of the TSG provide the best correlations with those in the Minamidani-1 tephra deposits in the Kinki, Chubu and Shin-etsu Districts.
Tajikara, Masayoshi*; Yasue, Kenichi; Yanagida, Makoto*; Furusawa, Akira*; Tanaka, Norifumi*; Morita, Yoshimune*; Sugai, Toshihiko
Chirigaku Hyoron, 84(2), p.118 - 130, 2011/03
Many papers reported that Quaternary climate and sea-level fluctuations have controlled riverbed elevation in the river basins in the northeastern Japan. However, in the southwestern Japan, such climatic-controlled riverbed fluctuations have not been reported, except a few reports based on uncertain chronological data. In this research, we investigated fluvial terraces along the Tokigawa river that flows through the low relief mountainous areas, and examined whether riverbed fluctuations similar to these in rivers in the northeastern Japan occurred in the river basin. We mapped fluvial terraces based on air photo analysis, and inferred the age and climate at the time of formation of these terraces based on 
C dating, tephra analysis, and pollen analysis. Based on results of these analyses, we concluded that the fluvial terraces in the river basin have been formed in consequence of the riverbed fluctuation linked to the climate change.
Tajikara, Masayoshi; Takada, Keita*; Furusawa, Akira*; Sugai, Toshihiko
Dai Yonki Kenkyu, 50(1), p.21 - 34, 2011/02
Three major fluvial terraces are developed well along the Kabura-gawa river, tributary of the Tone-gawa river. We detected cryptotephras in overbank and aeolian deposits covering the middle terrace gravels, and examined petrologic character. We also investigated petrologic character of the Iizuna-Kamitaru tephra (In-Kt) and the Iizuna-Nishiyama (In-Ny) tephra extracted from the outcrops near the Iizuna volcano. Based on these data, we identified possibly In-Kt and In-Ny tephra at the bottom of overbank deposits on the middle terrace of the Kabura-gawa river. This indicates that the middle terrace was formed through aggradation at glacial age of marine oxygen isotope stage 6. The Kabura-gawa river basin is located out of the previously reported distribution area of In-Kt. This fact implies that In-Kt is distributed more widely in the northern Kanto and southern Tohoku regions, and that In-Kt is useful as marker tephra of the middle Pleistocene in these regions.
Morita, Yoshimune*; Kamiya, Chiho*; Sasaki, Toshinori*; Miyagi, Toyohiko*; Sugai, Toshihiko; Yanagida, Makoto*; Furusawa, Akira*; Fujiwara, Osamu*
Kikan Chirigaku, 62(4), p.195 - 210, 2010/12
It is assumed that the variation of temperature and the precipitation with the climate change may affect geological environment such as the subsurface water flow. Therefore, as well as global climate change from the past to the present, investigation technology to grasp local climate change is indispensable. A palynological study was carried out using the sediment core taken from the Okute Basin, located in the northeast of Mizunami Underground Research Laboratory. As a result, it was appeared that in a interglacial epoch, there was much precipitation around this area, and that in a glacial epoch, became colder and more arid, compared with Kinki region in the same latitude. This shows that the modern analog method with pollen data from the sediment of the inland basin is effective technique to estimate a local climate change.
Ishii, Eiichi; Yasue, Kenichi; Ohira, Hiroto*; Furusawa, Akira*; Hasegawa, Takeshi*; Nakagawa, Mitsuhiro*
Chishitsugaku Zasshi, 114(6), p.286 - 299, 2008/06
no abstracts in English
Morita, Yoshimune*; Kamiya, Chiho*; Sasaki, Toshinori*; Miyagi, Toyohiko*; Sugai, Toshihiko*; Yanagida, Makoto*; Furusawa, Akira*; Fujiwara, Osamu*; Moriya, Toshifumi*
Kikan Chirigaku, 58(3), p.123 - 139, 2006/00
A palynological study was carried out using the 25.3 m long sediment core taken from Okute basin, Mizunami city, central Japan. Sediments of this core were accumilated for more than ca. 300,000 years. From the results of pollen analysis, the sediments are devided into 15 pollen assemblages zones. These changes show a repetition of five warm and four cool stages. Each stage corresponds to MIS 9 to 1. Consequently, a temperature of MIS 5 was higher than those of MIS 7 and 9. A temperature of MIS 9 was not so high.
Umeda, Koji; Furusawa, Akira*
Gekkan Chikyu, 26(6), p.395 - 400, 2004/06
no abstracts in English
Kubouchi, Akihiko*; Furusawa, Akira*
JNC TJ7420 2005-098, 364 Pages, 1998/03
JNC-TJ7420-2005-098.pdf:141.77MB
no abstracts in English
Umeda, Koji; Kusanagi, Megumi*; Furusawa, Akira*; Ui, Tadahide*
Kazan, 41(2), p.61 - 71, 1996/00
None
Tajikara, Masayoshi; Takada, Keita*; Furusawa, Akira*; Morita, Yoshimune*; Sugai, Toshihiko*
no journal, ,
We investigated fluvial terraces along the Kaburakawa River, in order to clarify the model of fluvial terrace development. Based on air photo analysis, fluvial terraces in the study area were classified into four categories (Q1-Q4). Existing papers reported that Q3 was formed in Marin Oxygen Isotope Stage (MIS) 2. In this study, we found a fragment of tree which is identified as 
or 
. This fact indicates that Q3 was formed in relatively cold age. Q2 is distributed at higher level than Q3. We found Iizuna-Kamitaru Tephra (Iz-Kt) at the lowermost part of aeolian deposits or uppermost part of overbank deposits in some outcrops of Q2 deposits. Since Iz-Kt is believed to fall at boundary of MIS 5 and 6, we concluded that Q2 deposits was accumulated in MIS 6 and that Q2 was incised in MIS 5.
Tajikara, Masayoshi; Yasue, Kenichi; Yanagida, Makoto*; Sugai, Toshihiko; Morita, Yoshimune*; Furusawa, Akira*
no journal, ,
no abstracts in English
Tajikara, Masayoshi; Yasue, Kenichi; Sugiyama, Shinji*; Takada, Keita*; Kato, Takayuki*; Sugai, Toshihiko; Morita, Yoshimune*; Furusawa, Akira*
no journal, ,
no abstracts in English
Ishii, Eiichi; Hiraga, Naoto; Yabuuchi, Satoshi; Yokota, Hideharu; Furusawa, Akira*
no journal, ,
no abstracts in English
Yasue, Kenichi; Hirouchi, Daisuke*; Kokubu, Yoko; Matsubara, Akihiro; Furusawa, Akira*
no journal, ,
In order to clarify the stratigraphic correlation around the fault and the timing of faulting event, we carried out radiocarbon dating of the black soil sampled from the trench wall of the Atera Fault. The dating results show that the soil ages varies from 4,000 to 2,000 years with depth. Black soil was deposited at approximately constant rate each at both sides of the fault in 4,000-2,000 years ago. This indicates that the fault wasn't displaced during this period. In the upper part, there is no variation in ages of black soils with depth. This suggests that sedimentation rate was faster. One of the causes that the sedimentation rate around the fault suddenly changes is fault displacement. It is thought that the faulting was about 2,000 years ago. About this timing, it is necessary to consider in behavioral segments of Atera fault zone in detail.
Yasue, Kenichi; Hirouchi, Daisuke*; Kokubu, Yoko; Matsubara, Akihiro; Furusawa, Akira*
no journal, ,
This study proposes the exact identification method of faulting events. Radiocarbon ages of the black soil collected continuously from lower to upper part clarify the timing of faulting events. We sampled the black soil without space from the excavated trench wall of the active fault. The soil ages in footwall varied from 9,500 to 2,000 years ago with depth. The soil deposited at approximately a constant rate. However, there are partially the anomalous ages. The anomalies are probably caused by fault displacements, which means the collapse of hanging wall with old soil and the making of depression at the footwall side. The anomalous ages may suggest that faulting events took place in about 7,500, 6,000, 3,500, and 2,000 years ago. Our future research will be to apply this method to the soil of other active fault trench wall to clarify the timing of faulting events.
Kagami, Saya; Yokoyama, Tatsunori; Umeda, Koji*; Yasue, Kenichi*; Niwa, Masakazu; Furusawa, Akira*; Tamura, Itoko*
no journal, ,
Tephrochronology is important to understand geotectonic events for the last few Myr. Tephra is usually characterized by petrographic characteristics and chemical compositions (mainly major elements) of volcanic glass shards. When tephras similar in the characteristics are discriminated, trace element compositions are valid for identification of tephra. We focus on the enrichment of the database of trace elements compositions in widespread tephras, which is not reported enough. We used EPMA and LA-ICP-MS for major and trace element concentration of volcanic glass shards in Znp-Ohta tephra and Tng tephra, of which major elements similar to Znp-Ohta tephra. In this study, it was clear that Znp-Ohta tephra had zirconium concentration [Zr] = 44-58 ppm and Zr/Pb = 2.5-3.4, while Tng tephra had [Zr] = 70-81 ppm and Zr/Pb = 3.8-4.6. Znp-Ohta and Tng tephras were discriminated not only by characteristic type, Ba/La, and La/Y of glass shards (Tamura and Yamazaki, 2004) but also by Zr-Pb correlation. In the future, we compare the trace element concentrations of Znp-Ohta tephra in multiple sites for evaluation of secondary effect during the deposition.
