著者
早川 由紀夫 由井 将雄
出版者
Japan Association for Quaternary Research
雑誌
第四紀研究 (ISSN:04182642)
巻号頁・発行日
vol.28, no.1, pp.1-17, 1989-05-31 (Released:2009-08-21)
参考文献数
23
被引用文献数
22 23

The eruptive history of the Kusatsu Shirane volcano is well described by means of 14 beds of key tephra and intercalating loess soil. Three eruptive stages are recognized. During early or middle Pleistocene the Matsuozawa volcano was formed; this is the first stage. The second stage was initiated by effusion of the Horaguchi lava, which was followed by eruptions of the Oshi pyroclastic flow, older lava flows, 3P pumice fall, and Yazawahara pyroclastic flow. Brown loess soil about 10m thick covering these deposits indicates that a dormant period of more than 100, 000 years followed this stage. The summit area upheaved about 400m or more against the foot of the volcano during this period, as is suggested by the extraordinarily steep (6.1°-3.0°) surface of the Oshi ignimbrite plateau. The third stage, which started about 14, 000 years ago, is the formation of three pyroclastic cones on the summit and contemporaneous effusion of the younger lava flows, e. g. the Kagusa lava of 7, 000 years ago and the Sessyo lava of 3, 000 years ago. In historic times, phreatic explosions have frequently occurred on the summit crater, Yugama. This means that the present belongs to the third stage. It is unlikely that eruptions of the third stage are caused by cooling of the magma chamber which was active in the second stage. The activity of the third stage seems to denote arrival of a new magma chamber at shallow depth.
著者
大熊 孝
出版者
Japan Association for Quaternary Research
雑誌
第四紀研究 (ISSN:04182642)
巻号頁・発行日
vol.35, no.3, pp.235-246, 1996-07-31 (Released:2009-08-21)
参考文献数
21

河川技術を思想的段階,普遍的段階,手段的段階の3段階に分類し,その観点から越後平野における治水史を松ヶ崎放水路と大河津分水を中心に概観し,それぞれの技術の発展段階に対応した開発の重要性について述べる.
著者
森脇 広 小林 哲夫
出版者
Japan Association for Quaternary Research
雑誌
第四紀研究 (ISSN:04182642)
巻号頁・発行日
vol.41, no.4, pp.223-224, 2002-08-01 (Released:2009-08-21)
参考文献数
10
被引用文献数
1
著者
山崎 晴雄
出版者
Japan Association for Quaternary Research
雑誌
第四紀研究 (ISSN:04182642)
巻号頁・発行日
vol.16, no.4, pp.231-246, 1978-02-28 (Released:2009-08-21)
参考文献数
32
被引用文献数
14 7

The Musashino Upland, a dissected fan of the Tama River in the western suburbs of Tokyo, is displaced by the Tachikawa fault, which runs in a NW-SE direction with long-continued flexure scarps.Using the tephrochronological method and data of water well logs, the author investigated geomorphic features and movement history of the fault in detail. It is thus revealed that the fault has displaced the terrace surfaces of various ages, including the Tc3 surface of 14, 000 years B.P. and the Holocene old stream channels (Fig. 1, Fig. 10). The Plio-Pleistocene sediments, buried under the Musashino Upland, have been vertically displaced about 70m at Hakonegasaki (Fig. 5, Fig. 6). This fault has only vertical displacement with no strike-slip component, and the upthrown side of the fault is northest. The long-term average slip-rate, derived from the displacement of terrace surfaces, is the largest in the central part of the fault and gradually decreases toward the both ends. The maximum average slip-rate is 36cm/1000 years.The total length of the fault is 21km. If examined in detail, it may be divided into two segments from discontinuity of the geomorphic expression and difference in the long-term slip-rate (Fig. 11). No sign of fault movement has been found from precise levelling across this fault for 40 years. So it is thought that fault movements had been recurred on this fault with large earthquakes in the late Quaternary period. The fault displacement in an earthquake, the earthquake magnitude, and its recurrence interval are estimated at about 1.8m, M. 7.1, and 5, 000 years, respectively.There are two types of surface deformations along the Tachikawa fault. One is a flexure scarp of 100-300 meters in width (Fig. 8). This flexure scarp is thought to have been formed by the existence of thick unconsolidated fluvial gravel deposits overlying the faulted Plio-Pleistocene sediments. The other is a broad undulation of a few kilometers in a half-wave length across the fault trace (Fig. 12). This undulation seems to reflect the elastic dislocation of the crust due to the movements of the Tachikawa fault.
著者
埴原 和郎
出版者
Japan Association for Quaternary Research
雑誌
第四紀研究 (ISSN:04182642)
巻号頁・発行日
vol.12, no.4, pp.265-269, 1974-02-28 (Released:2009-08-21)

In this paper, the author discussed man's adaptation to the cold and formation of the northern Mongoloids in the light of human adaptability to the climatic conditions.It is widely known that the mammals generally show several adaptations to the climate, among which the most effective factors seem to be the light and the temperature. For instance, in the field of mammalian ecology, the rules proposed by GLOGER, BERGMANN and ALLEN are generally accepted, and they can be also applied on microevolution of the human populations to some extent. Thus, it is said that the Caucasoids have adapted to the cold and moist climate with low radiation of ultraviolet rays, and the Negroids to the environment with high temperature and excessive radiation of ultraviolet rays. In parallel to this, the Mongoloids are regarded as having adapted to the very low temperature and dry weather.However, adaptation in this direction has likely occurred in or just after the latest stage of the Upper Paleolithic, because the Mongoloids from this stage such as the Upper Cave Men show almost no evidence of adaptation to the extremely cold temperature.In this respect, the modern Mongoloids living in the arctic areas may be regarded as the people who acquired their adaptability to the cold in relatively recent stages of evolution. On the other hand, we can find some other populations who retain more or less archaic characters of the Mongoloids in peripheral areas of the Asian and the American Continents, and even in the sub-arctic areas.For instance, the Ainu has so far been attributed their origin to the Caucasian stock. Several recent findings on their blood composition, dermatoglyphics and dental characteristics, however, show close affinity to the Mongoloids.On the other hand, the Ainu still shows unique characteristics in quite rich beard and body hairs, relatively thin subcutaneous fat, partially projected facial bones, etc., and these characteristics do not show high degree of adaptability to the cold climate.On the basis of these fact, it is quite likely that the Ainu might be one of branches of the Mongoloid stock who has less experience to live under the extremely cold environment, and still retains some archaic characters compared with the neighbouring populations. Naturally, this hypothesis should be checked by several other data from the fields of anthropology, prehistory, geology, and other related sciences.
著者
石井 武政 磯部 一洋 相原 輝雄
出版者
Japan Association for Quaternary Research
雑誌
第四紀研究 (ISSN:04182642)
巻号頁・発行日
vol.26, no.1, pp.85-92, 1987-05-31 (Released:2009-08-21)
参考文献数
18
被引用文献数
1 1

Gentle slopes are distributed between uplands and lowlands in the Tsukuba Upland area, Ibaraki Prefecture, Japan. These slopes are dominant on the left bank side of streams flowing to the west and on the right bank side of streams flowing to the southeast. Opposite side slopes, in contrast, are generally steep. In other words, topography along the streams in upland areas shows an asymmetrical valley pattern.Drilling samples show that the upland is occupied, from top to baseward, by the Younger Loam (equivalent to the Tachikawa and Musashino Loams) and the Joso and Narita Formations of Quaternary age. The gentle slopes are underlain by slope deposits of poorly sorted silty sands and gravels 1-3 meters thick. The deposits consist of particles essentially derived from the Joso Formation.The slope deposits lie unconformably on the Joso and Narita Formations and are overlain by the upper Younger Loam which has AT (Aira-Tn Volcanic Ash) dated at 21, 000-22, 000y. B. P. in its basal part.This stratigraphic evidence indicates that the slope deposits were formed during the last glacial age. It is assumed, from the relation between the slope direction and the frequency of slope cryoturbation in the winter season, that the slope deposits were accumulated by refrigeration in the cold climates of the late Pleistocene.
著者
多 里英 公文 富士夫 小林 舞子 酒井 潤一
出版者
Japan Association for Quaternary Research
雑誌
第四紀研究 (ISSN:04182642)
巻号頁・発行日
vol.39, no.1, pp.1-13, 2000-02-01 (Released:2009-08-21)
参考文献数
26
被引用文献数
6 4

青木湖周辺には,後期更新世から完新世にかけての,おもに河成や湖成の堆積物が断片的に分布しており,下位より藪沢層,崩沢層,神城砂礫層,佐野坂崩壊堆積物,青木湖成段丘堆積物,青木湖底堆積物に分けられる.指標テフラと岩相対比によって,それらの相互関係を明らかにした.佐野坂崩壊堆積物の上位には,Dpm火山灰層がのるとされていたが,それを再堆積物と判断し,周辺の地史を次のように推定した.藪沢層は,比較的広い谷の中を南がら北へ流れる蛇行河川によって形成された.その時代は5万年前以前の寒冷な時期である.約5万年前,その河川は狭い谷の中を流れる網状河川に変化した.この堆積環境の変化は,DKP火山灰層を挾む崩沢層と神城砂礫層中部が礫を主体とすることにより示されている.約3万年前に,西方の仁科山地で大規模な地すべり崩壊が起こり,佐野坂丘陵が形成された.この崩壊堆積物は川をせき止め,丘陵の南側に深い湖(青木湖)を形成した.佐野坂丘陵の北側の凹地には支谷からの堆積物供給が多く,徐々に埋積されて,現在の神城盆地を形成するようになった.
著者
桑畑 光博
出版者
Japan Association for Quaternary Research
雑誌
第四紀研究 (ISSN:04182642)
巻号頁・発行日
vol.41, no.4, pp.317-330, 2002-08-01 (Released:2009-08-21)
参考文献数
66
被引用文献数
6 7 2

鬼界アカホヤ噴火は,九州の縄文土器編年に対応させると,轟A式古段階から新段階の間に起こったと推定される.また,九州のほぼ全域に展開していた轟A式土器の製作情報が,噴火の影響によって断絶することはなく,土器文化は継続したと推察される.他方,約半分の地域が鬼界アカホヤ噴火に伴う火砕流の直撃を受けたとされる南九州地方を対象として,鬼界アカホヤ降下後の遺跡の状況から生活環境の回復過程をみると,鬼界アカホヤ噴火直後には,南九州中部以北にしか遺跡の分布は認められず,それ以南ではしばらく生活が再開されなかったようである.轟B式中段階(約5,500yrs BP)になると,南九州本土においては,定着的な遺跡の形成が各地に認められる.しかし,鬼界カルデラにより近い大隅諸島や薩摩・大隅半島の南端部では,轟B式中段階になっても遺跡の規模は貧弱であり,定着的な遺跡が形成される時期は,さらにあとの曽畑式期(約5,100yrs BP)以降である.また,鬼界アカホヤ噴火後まもない時期には,南九州のほぼ全域において,堅果類の加工具である磨石・石皿類の割合が極端に少ないという傾向が認められる.このことから,噴火の影響によって,堅果類を生産する森林植生は大きなダメージを受けていたと推察される.磨石・石皿類が増加し,森林植生の回復がうかがわれる時期は,南九州の中部以北では遅くとも轟B式中段階以降であり,南部においては轟B式新段階から曽畑式期以降であると考えられる.
著者
早川 由紀夫
出版者
Japan Association for Quaternary Research
雑誌
第四紀研究 (ISSN:04182642)
巻号頁・発行日
vol.30, no.5, pp.391-398, 1991-12-25 (Released:2009-08-21)
参考文献数
24
被引用文献数
11 5

Tephra provide extremely useful sedimentary beds for Quaternary research because they are highly reliable time markers. Tephra studies in Japan have advanced primarily on this basis. Because tephra themselves are products of volcanic eruptions it is quite possible to study explosive eruptions using tephra beds. The thickness of the beds tells us the magnitude of the eruption, while the dispersal pattern of the tephra tells us the intensity of the eruption. The mode of eruption is known by the grain-size characteristics of the tephra deposits. The life history of a volcano can be revealed by alternations of tephra and loess beds.
著者
細野 衛 佐瀬 隆
出版者
Japan Association for Quaternary Research
雑誌
第四紀研究 (ISSN:04182642)
巻号頁・発行日
vol.28, no.2, pp.79-93, 1989-07-31 (Released:2009-08-21)
参考文献数
42
被引用文献数
2 1

The old burial mound“Komatsu Kofun, ”which has been buried under the River Tone alluvial soil, was discovered at Hanyu City in Saitama Prefecture. The bottom of the chamber is situated 3 meters below the surface. It is considered that the mound was sunk by the Kanto Basin-forming movement, and has been buried by river sediments.In this study, the location of Kofun ground was defined by pedological analyses of soil just under the chamber. The following conclusions can be drawn by making a comparison between these data and the characteristics of nearby Kanto loam terraces.1) The basement of the burial mound is Tachikawa loam formation (tephra layer), which was formed in the Late Pleistocene, and Kofun was constructed on Kanto loam terrace. The formation is tephra in situ, not banked.2) As there is no soil horizon A (Kuroboku soil) at the bottom of the chamber, it is estimated that the chamber was set on Tachikawa loam formation, which acquires bearing capacity by stripping coarse structural Kuroboku soil.3) Tachikawa loam formation of the Kofun ground is air-borne and air-laid tephra, and non-tephra particles are also included in it. This mixed-particle tephra is not so extensive as to change the pedological characteristics of the Tachikawa loam formation.
著者
鈴木 美保 五十嵐 彰 大沼 克彦 門脇 誠二 国武 貞克 砂田 佳弘 西秋 良宏 御堂島 正 山田 哲 吉田 政行
出版者
Japan Association for Quaternary Research
雑誌
第四紀研究 (ISSN:04182642)
巻号頁・発行日
vol.41, no.6, pp.471-484, 2002-12-01 (Released:2009-08-21)
参考文献数
36

本論では,剥片の製作痕跡から石器製作時に使用されたハンマー素材を推定する方法を,実験考古学的手法によって考察した.硬質の石,軟質の石,鹿角,木の4素材のハンマーを用いて,実験的に製作した剥片痕跡の諸属性を検討した結果,ハンマー素材の差は剥片の剥離開始部分の属性に特徴的に現れることが判明した.そして,それらの諸属性を組み合わせることで,各素材と相関性の高い5類型に区分をすることができた.また,各素材と剥離対象物である黒曜石のビッカース硬さ測定した結果,その類型区分はハンマー素材と剥離対象物とのビッカース硬さの関係に相関していることも明らかになった.さらに,南関東地方の後期旧石器時代の2遺跡出土の剥片群に対してハンマーの推定を試みたところ,いずれも軟質の石によって製作されたものである可能性が高いことがわかった.
著者
白石 建雄 新井 房夫 藤本 幸雄
出版者
Japan Association for Quaternary Research
雑誌
第四紀研究 (ISSN:04182642)
巻号頁・発行日
vol.31, no.1, pp.21-27, 1992-02-29 (Released:2009-08-21)
参考文献数
17
被引用文献数
9 8

秋田県男鹿半島の上部更新統潟西層から阿蘇4火砕流 (Aso-4pfl) および三瓶木次軽石 (SK) 由来の漂流軽石と阿蘇4火山灰 (Aso-4) が発見された. SK漂流軽石は模式地の潟西層最上部付近に含まれ, Aso-4pfl由来の漂流軽石はAso-4直上に存在する. このことにより, 潟西層は関東地方の下末吉層より新しく, ほぼ小原台期に対比されること, ならびにSKおよびAso-4が堆積した7~9万年前には日本海を北上する海流があったことが明らかになった. また, 男鹿半島で下末吉層相当層と下末吉段丘に対比される段丘を確定することがこれからの課題となった.
著者
小野 映介 海津 正倫 鬼頭 剛
出版者
Japan Association for Quaternary Research
雑誌
第四紀研究 (ISSN:04182642)
巻号頁・発行日
vol.43, no.4, pp.287-295, 2004-08-01 (Released:2009-08-21)
参考文献数
33
被引用文献数
2 4

完新世後期の濃尾平野における土砂堆積域の変遷について,低地の地形・地質と遺跡の分布や遺物の検出状況をもとに検討した.濃尾平野では縄文時代中期後葉(4,300yrs BP)以降,木曾川扇状地東部を中心に遺跡が分布するようになり,縄文時代後期末(3,000yrs BP)と弥生時代前期末(2,200yrs BP)の2度の画期を経て,西側と南側の地域にその分布域を段階的に拡大させた.各遺跡では,地表面下2m以浅の黒色有機物層やシルトを主体とした細粒堆積物層から遺物が出土しており,遺跡が立地して以降,洪水による堆積物の供給を受けにくい環境が継続したことが推定された.これらから,濃尾平野では完新世後期に木曾川の主流および土砂の堆積域が低地東部から西部へと移行するとともに,堆積環境の安定域が西部や南部へ拡大したことが考えられる.このような変遷過程は,養老断層を境に沈降する西下がりの傾動運動と対応しており,その影響を受けたものと推定される.また,縄文時代晩期(3,000yrs BP)以降における木曾川の顕著な西流傾向と海側の地域における土砂の集中的な堆積は,「弥生の小海退」に相当する海岸線の海側への急速な前進のおもな要因となったと考えられる.
著者
Shigeo SUGIHARA Isao TAKAHARA Mamoru HOSONO
出版者
Japan Association for Quaternary Research
雑誌
The Quaternary Research (Daiyonki-Kenkyu) (ISSN:04182642)
巻号頁・発行日
vol.11, no.1, pp.29-39, 1972-05-25 (Released:2009-08-21)
参考文献数
33
被引用文献数
2 6

This thesis was written of the topography and volcanic ash layers (the so-called Kanto Loam) of the Musashino upland extending over the western region of Tokyo Metropolis. The results are summarized as follows:1) The geomorphic surfaces of the Musashino upland may be divided into Yodobashi, Narimasu, Akabane, Nakadai and Tachikawa terraces from older to younger in order. These terraces are covered with the volcanic ash layers. It was found that the older terraces are covered with the thicker volcanic ash layers, compared with the younger terraces.2) In classifying Yodobashi and Narimasu terraces, two pumice beds, namely SIP and Pm-1 found in the volcanic ash layers are used as key beds. In the case of Akabane and Nakadai terraces, TP would be used as key bed.3) Beneath the sediments of Yodobashi and Akabane terraces, observed are drowned valley features. Those valleys are filled up with marine sediments representing each of the transgression periods. The amounts of transgression are estimated several ten meters with Yodobashi terrace, and several meters with Akabane.
著者
原山 智 大藪 圭一郎 深山 裕永 足立 英彦 宿輪 隆太
出版者
Japan Association for Quaternary Research
雑誌
第四紀研究 (ISSN:04182642)
巻号頁・発行日
vol.42, no.3, pp.127-140, 2003-06-01 (Released:2009-08-21)
参考文献数
46
被引用文献数
11 13

飛騨山脈の隆起については,鮮新世後期から更新世初頭(2.7~1.5Ma)にかけて,最初の極大期があったとする点では,多くの研究者の意見が一致している.しかし,その後の第四紀の期間にテクトニックな隆起があったかどうかでは,意見が分かれていた.山麓の堆積物から隆起時期を推定する方法では,山脈の隆起がテクトニックなのか,アイソスタティックなのか,判定困難なため,本研究では飛騨山脈,爺ヶ岳一帯に分布する鮮新世後期~前期更新世の火山岩類の構造を解析した.この結果,これらの火山岩類はコールドロンをなしており,東に70°前後傾動していることが判明した.南方の高瀬川流域や槍穂高連峰での資料を加味すると,前期更新世後半(1.3Ma~)以降,飛騨山脈東半部の広い範囲で,東西圧縮場のもとでの挫屈による傾動・隆起を生じていることが明らかとなり,飛騨山脈の2段階にわたるテクトニックな隆起運動が明らかとなった.
著者
藤井 理行
出版者
Japan Association for Quaternary Research
雑誌
第四紀研究 (ISSN:04182642)
巻号頁・発行日
vol.34, no.3, pp.151-156, 1995-08-31 (Released:2009-08-21)
参考文献数
19
被引用文献数
2 2

氷河や氷床の涵養域では,雪とともにさまざまな起源を有する物質が年々堆積している.また雪が氷になる過程では,大気が気泡として取り込まれている.このように,氷河あるいは氷床から掘削により取り出したコアは,過去100~105年の気候や環境変動のタイムカプセルといえ,第四紀研究における分解能のよい情報を提供することになる.雪氷コアの解釈の上で重要なことは,コア年代の合理的な決定である.本論では,季節変化シグナルによる方法,年代示準シグナルによる方法,放射性同位体による絶対年代の決定法,氷の流動モデルによる方法を紹介する.
著者
氏家 宏
出版者
Japan Association for Quaternary Research
雑誌
第四紀研究 (ISSN:04182642)
巻号頁・発行日
vol.37, no.3, pp.243-249, 1998-07-31 (Released:2009-08-21)
参考文献数
19
被引用文献数
6 5

沖縄トラフは,琉球島弧の北西側に並走して発達し,さらに北西側に展開する広大な東シナ海大陸棚外縁を縁どっている.現在,そこに黒潮が流入しているが,最終氷期には,推定されている“琉球-台湾陸橋”によって流入を妨げられて,南琉球弧南方沖で大きく東へ転向していたと考えられている.この仮説を琉球弧周辺海域,特に沖縄トラフから得た多数のピストン・コアの安定酸素同位体比測定,タンデム加速器質量分析計による14C年代測定,浮遊性有孔虫群集解析などから確かめた.さらに沖縄トラフのコアでは,浮遊性有孔虫Pulleniatinaグループが最終氷期と同様に,約4,400年前以後約1,000年間,ほぼ欠如に近い産出を示すことから,陸橋区域に黒潮の本格的な流入を妨げるバリヤーが形成され,黒潮本流の転向と南方へのシフティングを促したと推論した.この事件が,これまでにいわれている前期縄文時代後半における寒冷化をもたらしたのかもしれない.
著者
馬場 悠男
出版者
Japan Association for Quaternary Research
雑誌
第四紀研究 (ISSN:04182642)
巻号頁・発行日
vol.37, no.3, pp.259-266, 1998-07-31 (Released:2009-08-21)
参考文献数
31

現代日本人の成立に関しては,明治時代から多くの研究者によって,北方および南方からやってきた複数の起源集団による混血の可能性が示唆され,今日でも広く認められている.すなわち,東アジア全体として,更新世末期(3~1万年前)には南方系と考えられる人々が分布していたが,最近(1万年~5,000年前)は北方系と考えられる人々が急速に拡大した,という理解の上に立って,縄文人は南方系の先住集団であり,弥生人は北方系の渡来集団であって,両者の混血によって現代日本人が成立した,と解釈するものである.このような解釈をまとめたのが埴原和朗の「二重構造モデル」である.その際の,南方および北方からの移動のルートとしては,南西陸橋あるいはその付近の海路が有力であるが,北方のルートの可能性も指摘されている.少なくとも,弥生人の渡来に関しては,九州北部を中心とする地域に集中したことはまちがいない.なお,尾本恵市は,遺伝学的データから,更新世後期にすでに南方系アジア人と北方系アジア人が分化していたと考えている.そうすると,縄文人も北方系の人々に起源を持つことになる.筆者は,化石人類の頭部形態から,縄文人の起源は更新世末期に北東アジア沿岸部に住んでいた人々であると考えている.
著者
桑原 徹
出版者
Japan Association for Quaternary Research
雑誌
第四紀研究 (ISSN:04182642)
巻号頁・発行日
vol.7, no.4, pp.235-247, 1968-12-20 (Released:2009-08-21)
参考文献数
61
被引用文献数
33 26

The tectonic development of the Noobi sedimentary basin is discussed in relation to crustal movements of southwest Japan in the period of the Quaternary.The basin is an eastern part of the Second Setouchi sedimentary province formed in the inland area of southwest Japan during the Plio-Pleistocene. In the Setouchi province, two types of tectonic movements originated in crustal undulation are recognized: Type-1 is of long-wave undulation which has formed the main depressional zone with parallel axis to the trend of the Setouchi province. Type-2 is of short wave undulation crossing, in almost cases, the trend of the axis of the province, which has formed the alternating arrangement of basin and ridge in the depressional zone.From the tectonic point of view, the province is divided into three crustal blocks from east to west:-(1) Chubu, (2) Kinki and (3) Chugoku.The eastside of the Chubu block is marked off by the Fossa Magna, and westside by the Tsuruga-Ise bay line. The Noobi basin is situated in the western end of this block. A subsidence of the basin has been largely caused by tilting movements of the block active since the Pliocene, and less by the crustal undulation. This tilting block movement in large scale is a tectonic movement characteristic in the Setouchi province. And also in the Chubu block, the trend of axis of type-2 undulation changes into parallel direction to that of the Setouchi province.The rate of the tilting movement in the Noobi basin seems to increase in the latest periods. The mean rate of the tilting movement is estimated to be 7×10-8 per year during the latest 35, 000 years according to geological evidences. This figure is almost the same to the one of the recent crustal movements measured geodetically in Japan.
著者
町田 洋 松島 義章 今永 勇
出版者
Japan Association for Quaternary Research
雑誌
第四紀研究 (ISSN:04182642)
巻号頁・発行日
vol.14, no.2, pp.77-89, 1975-06-30 (Released:2009-08-21)
参考文献数
21
被引用文献数
4 8

The tephrochronological study of the eastern foot of Mt. Fuji (Fig. 1) would provide abundant data for analyzing not only eruptive history of Fuji volcano but also other late-Quaternary events, because there lies a large quantity of tephra derived mainly from the volcano. Several marker pumice layers are found sandwiched within great numbers of scoria sheets and are correlated with those in south Kanto, where stratigraphic position and radiometric age of them were well established (Table 1, 2 and Fig. 3). The revised stratigraphy and chronology in this area should play significant role in discussing several Quaternary problems around there.1) Mt. Fuji volcano became active ca. 80, 000 y. B.P., when the most important marker pumice, the Ontake Pm-I, showered. Since then, the eruption of “Older Fuji stage” had occurred more or less continuously until ca. 10, 000 y. B. P. without any significant periods of quiescence. The Older Fuji tephras are estimated at approximately 250km3 in volume, which are distributed extensively in south Kanto (Fig. 6). These explosive activities ended at about 10, 000 y. B. P. and there followed a long quiescent period, succeeded by “Younger Fuji stage”.2) The fluvial formation formerly called “Suruga Gravels” is a deposit of the ancient Sakawa river ca. 80, 000 y. B. P. The ancient river took its rise in Tanzawa mountains and might have flowed west- or southwestward into Suruga bay, instead of Sagami bay, the present course flows into. The change in river course appears to have taken place during the period from 80, 000 to 60, 000 y. B. P., associated with the growth of the volcanic edifice of Mt. Fuji (Fig. 5).3) The Kannawa fault, one of the most important tectonic lines in central Japan, runs east to west along the northern margin of the area. It branches westwards into two faults; Kn and Ks. Along the Kn fault a thrust is found dipping northward, whereas along most of the course the fault plane is nearly vertical (Fig. 9). The movements of the both faults are younger than the Suruga Gravels, which is displaced vertically more than 50 metres during the last 80, 000 years.