著者

島弧深部構造研究グループ 赤松 陽 原田 郁夫 飯川 健勝 川北 敏章 小林 和宏 小林 雅弘 小泉 潔 久保田 喜裕 宮川 武史 村山 敬真 小田 孝二 小河 靖男 佐々木 拓郎 鈴木 尉元 鈴木 義浩 山崎 興輔

出版者

地学団体研究会

雑誌

地球科学 (ISSN:03666611)

巻号頁・発行日

vol.63, no.1, pp.9-27, 2009

参考文献数

11

被引用文献数

2

---

島弧深部構造研究グループは,気象庁2006年刊行の地震年報によって,日本列島とその周辺地域で1983年から2005年までに発生した地震の震源分布を検討した.そのうち100km未満の地震はM4.5以上,100km以深の地震についてはM3以上のものを取り上げ,陸上は400mごとの等高線,海域は400mごとの等深線で示された地形図上にプロットして検討資料とした.震源の空間的な分布を明らかにするために,地震の分布する空間の下底の等深線を描いた.等深線は,北海道から千島列島に沿う地域では千島・カムチャツカ海溝付近から北西方に,本州に沿う地域では日本海溝付近から西方に,伊豆・小笠原諸島に沿う地域では伊豆・小笠原海溝付近から南西方に,九州ないし南西諸島とその周辺地域では,琉球海溝付近から北西方に次第に深くなるような傾向を示す.より細かく検討すると,等深線は単純ではない.等深線中に,直線状ないし弧状に走り,隣の単元に数10kmあるいはそれ以上に不連続的に変位する単元を識別できる.このような不連続部は,北海道・千島列島地域では北西-南東方向に走り,各深さのこのような不連続部は雁行状に並ぶ.これらの不連続変位部に境された一つの単元の拡がりは100ないし400kmである.より大きな不連続線として国後島の東縁付近と北海道中央を通るものが識別される.千島海盆付近で等深線は南東方に張り出しているが,これは千島海盆付近で震源分布域が下方に膨らんでいることを示す.本州東北部と,日本海の東北部および中央部では,直線状あるいは弧状に走る等深線を北西-南東と東西方向の不連続線が切る.これらによって境された単元の拡がりは100ないし200kmである.より大きな不連続線として,日本海南西部から本州の中央部を走る線が識別される.伊豆・小笠原諸島地域では,直線状あるいは弧状の等深線を切る不連続部は東北東-西南西方向をとる.これら不連続変位部に境された単元の拡がりは数10ないし200kmである.より大きな不連続線として伊豆・小笠原諸島北部と中央部を走るものが識別される.九州・南西諸島とその周辺地域では,直線状あるいは弧状の等深線を切る不連続部は東北東-西南西方向に走る.これら不連続部に境された単元の拡がりは80ないし250kmである.より大きな不連続線として大隈諸島と奄美大島間を走る線が識別される.このように,和達・ベニオフ面とよばれるものは地塊構造を暗示させる垂直に近い線によって境された,より小さな分節にわかれることが明らかになった.

著者

平山 次郎 鈴木 尉元

出版者

地学団体研究会

雑誌

地球科學 (ISSN:03666611)

巻号頁・発行日

vol.22, no.2, pp.43-62b, 1968-03-25

---

A sedimentological study was made of the Flysch-type alternations of Otadai formation, Kazusa group deposited in the central part of the Boso peninsula in upper Pliocene epoch (Fig. 2). The formation consists of rhythmic alternation of sandstone and mudstone and the relative amounts of the two rocks vary in places. Each layer is correlated for more than 30 km in extent, as it has their own characteristics in thickness, texture, composition and colour and is arranged in similar manner at the neighbouring sections (Fig. 3, 4). Several key beds of tuff are the most important in the correlation because of their distinct features. The shape, textural distribution and grain size variation in the layers has been definitely shown by the method stated above. The thicker each layer of sandstone is, the more spacial extent it acquires in general. The layer over 10 cm in thickness at the thickest part reaches more than 30 km in extent. It is asymmetrical in shape owing to the more rapid decrease toward west (Fig. 6). On the other hand, the thickness of mudstone layers increases gradually toward west within the studied area but seems to decrease very rapidly westward (Fig. 5). It is concluded that the thickness variation of sandstone and mudstone assembly is determined by sandstone, that is, the layers of sandstone are very sensitive to the subsidence of the basin. Of course, the subsidence is the neccessary condition for the formation of layers. A layer consists of lamina which are units of mass movement of grains, as will be seen from the Photo. 1. A relatively thick sandstone layer is divided into three intervals based on the nature of lamina, namely, massive graded, parallel-laminated and cross-laminated intervals from the base respectively. But a thin sandstone layer is devoid of massive graded interval and/or parallel-laminated intervals. The arrangement of these lamina is closely related to the thickness variation of a layer (Fig. 6). The grain size distribution and consituents in a layer are also related to the textural arrangement as well as the shape (Fig. 9). The boundaries of textures are nearly parallel to the isometrical lines of median diameter of grain size and sorting coefficient. Shell fragments are concentrated at the bottom of the graded interval, while pumice and plant fragments are often seen in the parallel and cross-laminated intervals. The grain size variation in the mudstone layer seems to be more monotonous and the mean size and sand grain content gradually decrease toward west. As will be known from the fact stated above, sandstone layers are very different from mudstone layers in many respects. And it is observed that the sandstone layer is formed by different way from the mudstone. The inference is substanciated by the difference of faunal assemblages found in both layers. The sandstone has the shell fragments and worn-out foraminifers which are found in the upper neritic zone in the recent environment, while molluscan shells and foraminifers contained in the mudstone are similar to the fauna living in the bottom over 400 m in depth in the Pacific off the Boso peninsula. This fact indicates that sand deposited temporarily under the bottom of shallow sea is transported into the bathyal environment where mud is usually deposited. The direction of current transporting sand grains should be from west to east as is assumed from the sole markings developed under the bottom of sandstone layers and cross laminations (Fig. 10). The nature of flow is inferred from the result of laboratory experiments and observations of alluvial channels. It is controlled by many variables such as depth, slope, size and shape of grains, viscosity and density of sediment-water mixture, etc. So the concept of flow regime (SIMONS & RICHARDSON, 1961) is very useful as it allows grouping of the combined effects of those factors. The classification of flow regime is based on form of the bed configuration, mode of sediment transport, process of energy dissipation and phase relation between the bed and water surface (Fig. 11). According to these elements, it is divided into lower and upper flow regimes (Fig. 11). In the lower flow regime, lamina which are horizontal or inclined 10 degrees or less down stream are well developed, while lamina is not distinct in the upper regime since amount of sediment transported by the flow increases and is not sorted. These changes of lamina might correspond to the textural arragement in a sandstone layer, from the base upward, massive graded, papallel laminated and cross-laminated intervals. It shows that a sandstone layer is formed by a flow which diminishes its energy gradually. Sand mass deposited in the shallow sea collapses just like a landslide and then slides down the slope which is maintained by the subsidence of the basin. It fills the subsiding areas and the relatively flat slope is formed and then mud particles fall down uniformly on it. During the deposition of mud, subsidence of the ground is continued and the depositional areas for sandstone are prepared.

著者

鈴木 尉元

出版者

地学団体研究会

雑誌

地球科学 (ISSN:03666611)

巻号頁・発行日

vol.58, no.1, pp.61-64, 2004-03-25 (Released:2017-07-14)

著者

鈴木 尉元 原田 郁夫

出版者

地学団体研究会

雑誌

地球科學 (ISSN:03666611)

巻号頁・発行日

vol.60, no.6, pp.489-500, 2006-11-25

被引用文献数

1

---

2004年10月23日に発生した中越地震(M6.8)は,東山背斜南部の川口町北方約7km,深度13kmに発生した地震であるが,この地震にともなって,東山背斜から越後山脈との境界を流れる破間川・魚野川付近にまで余震活動が行われた.この地震に際して東山背斜にそって背斜状に隆起し,隆起量は小千谷・川口間で60cm以上に達した.中越地震の震度は,東山背斜とその周辺地域は震度6,新潟県中・南部は震度5を記録したが,この震度5は東北日本南部の各地で記録された.その内,能登半島北部から東京湾付近に至る西北西-東南東方向の震度4を示した帯状地帯の各地に出現した点が注目される.本州東北部の南部の地震活動は,2003年7月26日の宮城県北部地震以来活発化している.その活動域は,朝日山地・奥羽山脈・飯豊山地・越後山脈・足尾山地から構成される脊梁山地西側の信濃川地震帯,その東縁地域,阿武隈山地東縁ないし関東平野に至る地域からその太平洋沖合地域である.中越地震はその一端をなすもので,信濃川地震帯にそうものである.このような本州東北部の南部の地震活動が,西部,中央部,東部がお互いに相呼応して行われることは,1800年代以後の地震活動に共通してみられる傾向である.日本列島は,一辺40ないし50kmの一等三角点網に覆われていて,数10年に一回の割合で改測が行われている.これまで公表されている2回の改測結果の解析によると,最大剪断歪みの大きくなる地域はほぼ決まっており,破壊的地震はそのような地域に発生している.この歪みの集積する地域は,60kmないし120kmよりも深い地震の活動する地域に当たっていることから,この地帯は数10kmよりも深い根をもつものと考えられる.本州東北部の南部の地震活動が,10ないし20年前後の活動期に各所で行われるのは,本州が全体として隆起し,周辺海域が沈降する運動が進行する中で,本州の中の山地の隆起,平野と盆地の沈降運動が進行し,このような運動にともなって各構造単元の境界付近に歪みが集積し,それら各所の歪みが断層の活動にともなう地震活動によって解放されることによるものと考えられる.したがって地震予知の体制は,このような規模の地殻変動と地震活動の監視を基本とすべきであると考える.

著者

鈴木 尉元

出版者

一般社団法人 日本地質学会

雑誌

日本地質学会学術大会講演要旨 (ISSN:13483935)

巻号頁・発行日

vol.2003, 2003

著者

鈴木 尉元

出版者

地学団体研究会

雑誌

地球科学 (ISSN:03666611)

巻号頁・発行日

vol.58, no.1, pp.61-64, 2004

参考文献数

8

著者

平山 次郎 鈴木 尉元

出版者

地学団体研究会

雑誌

地球科学 (ISSN:03666611)

巻号頁・発行日

vol.22, no.2, pp.43-62b, 1968-03-25 (Released:2017-07-26)

---

A sedimentological study was made of the Flysch-type alternations of Otadai formation, Kazusa group deposited in the central part of the Boso peninsula in upper Pliocene epoch (Fig. 2). The formation consists of rhythmic alternation of sandstone and mudstone and the relative amounts of the two rocks vary in places. Each layer is correlated for more than 30 km in extent, as it has their own characteristics in thickness, texture, composition and colour and is arranged in similar manner at the neighbouring sections (Fig. 3, 4). Several key beds of tuff are the most important in the correlation because of their distinct features. The shape, textural distribution and grain size variation in the layers has been definitely shown by the method stated above. The thicker each layer of sandstone is, the more spacial extent it acquires in general. The layer over 10 cm in thickness at the thickest part reaches more than 30 km in extent. It is asymmetrical in shape owing to the more rapid decrease toward west (Fig. 6). On the other hand, the thickness of mudstone layers increases gradually toward west within the studied area but seems to decrease very rapidly westward (Fig. 5). It is concluded that the thickness variation of sandstone and mudstone assembly is determined by sandstone, that is, the layers of sandstone are very sensitive to the subsidence of the basin. Of course, the subsidence is the neccessary condition for the formation of layers. A layer consists of lamina which are units of mass movement of grains, as will be seen from the Photo. 1. A relatively thick sandstone layer is divided into three intervals based on the nature of lamina, namely, massive graded, parallel-laminated and cross-laminated intervals from the base respectively. But a thin sandstone layer is devoid of massive graded interval and/or parallel-laminated intervals. The arrangement of these lamina is closely related to the thickness variation of a layer (Fig. 6). The grain size distribution and consituents in a layer are also related to the textural arrangement as well as the shape (Fig. 9). The boundaries of textures are nearly parallel to the isometrical lines of median diameter of grain size and sorting coefficient. Shell fragments are concentrated at the bottom of the graded interval, while pumice and plant fragments are often seen in the parallel and cross-laminated intervals. The grain size variation in the mudstone layer seems to be more monotonous and the mean size and sand grain content gradually decrease toward west. As will be known from the fact stated above, sandstone layers are very different from mudstone layers in many respects. And it is observed that the sandstone layer is formed by different way from the mudstone. The inference is substanciated by the difference of faunal assemblages found in both layers. The sandstone has the shell fragments and worn-out foraminifers which are found in the upper neritic zone in the recent environment, while molluscan shells and foraminifers contained in the mudstone are similar to the fauna living in the bottom over 400 m in depth in the Pacific off the Boso peninsula. This fact indicates that sand deposited temporarily under the bottom of shallow sea is transported into the bathyal environment where mud is usually deposited. The direction of current transporting sand grains should be from west to east as is assumed from the sole markings developed under the bottom of sandstone layers and cross laminations (Fig. 10). The nature of flow is inferred from the result of laboratory experiments and observations of alluvial channels. It is controlled by many variables such as depth, slope, size and shape of grains, viscosity and density of sediment-water mixture, etc. So the concept of flow regime (SIMONS & RICHARDSON, 1961) is very useful as it allows grouping of the combined effects of those factors. The classification of flow regime is based on form of(View PDF for the rest of the abstract.)

著者

鈴木 尉元

出版者

地学団体研究会

雑誌

地球科学 (ISSN:03666611)

巻号頁・発行日

vol.58, no.2, pp.127-130, 2004-03-25 (Released:2017-07-14)

著者

鈴木 尉元

出版者

地学団体研究会

雑誌

地球科学 (ISSN:03666611)

巻号頁・発行日

vol.59, no.5, pp.329-334, 2005-09-25 (Released:2017-07-14)

著者

鈴木 尉元

出版者

地学団体研究会

雑誌

地球科学 (ISSN:03666611)

巻号頁・発行日

vol.61, no.3, pp.217-221, 2007-05-25 (Released:2017-05-16)

著者

鈴木 尉元

出版者

地学団体研究会

雑誌

地球科学 (ISSN:03666611)

巻号頁・発行日

vol.61, no.3, pp.217-221, 2007

参考文献数

48

被引用文献数

1

著者

鈴木 尉元

出版者

日本地質学会

雑誌

地質學雜誌 (ISSN:00167630)

巻号頁・発行日

vol.84, no.3, pp.160-161, 1978-03-15

著者

鈴木 尉元

出版者

地学団体研究会

雑誌

地球科學 (ISSN:03666611)

巻号頁・発行日

vol.52, no.5, 1998-09-25