著者

瀬野 徹三

出版者

SEISMOLOGICAL SOCIETY OF JAPAN

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.64, no.2, pp.97-116, 2012-01-25 (Released:2012-02-20)

参考文献数

83

被引用文献数

13 23

---

Great earthquakes have historically occurred along the Nankai Trough. It has been said that they ruptured part or whole of characteristic fault planes A, B, C, D, and E repeatedly. However, there are a number of enigmas for their occurrence. Major ones are as follows. The 1944 Showa-Tonankai earthquake occurred only 90 years after the 1854 Ansei earthquakes. The 90-year period seems short compared with other time intervals of the historical earthquakes. The Tonankai earthquake did not rupture fault plane E west of the Suruga Trough, by some unknown reasons. The Tokai earthquake anticipated at fault plane E has not occurred yet since the Ansei-Tokai event even if a slow slip event occurred recently near the downdip end of its rupture zone. In this study, I propose a model to solve these enigmas. I characterize a fault plane of a great earthquake into a seismic-b.eq, a tsunami-b.eq, and a geodetic-b.eq, in which seismic waves, tsunamis, and crustal deformations are dominantly generated, respectively. I compare these different bands of rupture zones between the 1944 Showa-Tonankai and 1854 Ansei-Tokai earthquakes, the 1946 Showa-Nankai and 1854 Ansei-Nankai earthquakes, and the 1707 Hoei and other earthquakes, using seismic intensity data and previous studies on asperities, tsunamis, and crustal deformations. It is found that the Ansei-Tokai and Showa-Tonankai earthquakes scarcely shared their seismic-b.eqs. The tsunami- and geodetic-b.eqs of the Ansei-Tokai earthquake extended to the west of its seismic-b.eq, and was shared by, but did not cover the seismic-, tsunami- and geodetic-b.eqs of the Showa-Tonankai earthquake. It cannot thus be said that the Ansei-Tokai earthquake ruptured fault planes C+D+E or that fault plane E was left unbroken after the Showa-Tonankai earthquake. The occurrence of these two earthquakes is rather complementary from a viewpoint of the seismic-b.eq. The seismic-b.eq of the Ansei-Nankai earthquake also seems to have been different from and was located further north than that of the Showa-Nankai earthquake. On the other hand, the Hoei earthquake had a seismic-b.eq similar to those of the Showa earthquakes. I group historical great earthquakes into the Ansei-type or the Hoei-type, which has a seismic-b.eq similar to either of the Ansei or Hoei earthquake. It is likely that the Ansei-type earthquakes are the 684 Hakuho, 1096 Eicho-1099 Kowa, 1498 Meio, and 1854 Ansei earthquakes and recurred with a ∼400-year period, and that the Hoei-type earthquakes are the 887 Ninna, 1361 Shohei, 1707 Hoei, and 1944 Tonankai-1946 Nankai earthquakes and recurred with a ∼350-year period. Since the Showa-Tonankai earthquake was complementary to the Ansei-Tokai earthquake, the 90-year period between the two events is not a recurrence time and it is natural that the Showa-Tonankai did not rupture fault plane E. It is also natural that the next Tokai earthquake did not occur even if the slow slip event occurred at its downdip end, because it is expected to occur at least ∼200 years after present, because the earthquake precedent the Ansei-Tokai event would be the 1498 Meio earthquake.

著者

瀬野 徹三

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.114, no.3, pp.350-366, 2005-12-25 (Released:2009-11-12)

参考文献数

27

被引用文献数

2 3

---

Plate motions provide the most basic information on plate tectonics. I explain how to describe plate motions on the Earth mathematically, and how they can be determined. I review the history of the determination of global plate motions, the most recent of which has been derived by space geodetic techniques.

著者

瀬野 徹三

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.61, no.Supplement, pp.357-364, 2009-07-31 (Released:2013-11-21)

参考文献数

96

被引用文献数

1 2

---

History of studies of intraslab seismicity and its generation mechanisms, since the work by Wadati, is reviewed. Through the initial stage of studies of morphology of the intraslab seismicity, there followed the stage of discussion of focal mechanisms and terminal depths by mechanics and temperature of the slab. In 1970s, double seismic zones were discovered and their generation mechanisms were discussed in terms of bending or thermal stresses. In recent years, to overcome a difficulty that very high pressure prevents intraslab seismicity, dehydration embrittlement and phase transformation have been invoked for the mechanisms of intermediate and deep earthquakes, respectively. If the intermediate seismicity represents dehydration, it may give us a key to understand the distribution of fluids to the upper plate and to the seismogenic interplate thrusts, and finally to understand tectonics and volcanism in subduction zones.

著者

瀬野 徹三

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.46, no.4, pp.461-477, 1994-03-14 (Released:2010-03-11)

参考文献数

63

被引用文献数

1

---

Tectonics of the Taiwan region is reviewed. Relative plate motions so far obtained are described and rated. The most reliable solution gives 7.4cm/yr Philippine Sea-Eurasian motion in the N50°W direction in central Taiwan. Plate boundary geometries and modes of plate consumption in the region are discussed on the basis of geophysical, geological and geomorphological data. The major thrust zones at the Western Foothills and the Longitudinal Valley constitute mechanical plate boundaries, but a considerable fraction of the relative plate motion is also consumed by the strike-slip faulting off the southeast coast of Taiwan.The cause for the occurrence of the strike-slip faulting off the southeast coast of Taiwan is discussed based on the various models so far proposed. The bending of the Philippine Sea plate due to the subduction at the Ryukyu Trench and the collision in the Longitudinal Valley are similar to the tectonics of the Izu Peninsula region in Japan, and are the most likely cause for the strike-slip faulting.The reconstruction of the motion and plate boundaries in the vicinity of Taiwan for the past 4-6m. y. is reviewed. The Philippine Sea-Eurasian motion for the past 4 Ma is similar to the present one. The motion prior to 4 Ma may be more northward than present due to the absence of subduction at the Philippine Trench. The Luzon arc started to collide with the continental margin of S. E. China around 4 Ma.

著者

瀬野 徹三 丸山 茂徳

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.94, no.3, pp.141-155, 1985-06-25 (Released:2010-10-13)

参考文献数

85

被引用文献数

1 3

---

The models on the tectonic evolution of the Philippine Sea can be divided mainly into two:(1) entrapment of a normal ocean at 43Ma for the West Philippine Basin formation and back-arc basin formations caused by successive landward retreats of the upper Philippine Sea plate, and (2) back-arc basin formations caused by successive seaward retreats of the trench axis. These models are discussed on the basis of the presently available data.The island arc type volcanism at the northern half of the Palau-Kyushu Ridge since 48Ma, and the age-depth relation and chemistry of basalts at Sites 291 and 292 in the West Philippine Basin favor the back-arc spreading origin for this basin. In contrast, the chemistry of basalts at Site 447 and the large distance between the Central Basin Ridge and the northern Palau-Kyushu Ridge favor the entrapment origin for this basin. It is likely that the West Philippine Basin has formed under the unique situation of the ocean basin formation, i.e., with subduction at its northern margin and a spreading center far from this subduction zone.Subduction or collision of the aseismic ridges in and around the Philippine Sea is discussed in terms of the crustal structure of the ridges, seismicity, and onland geology. It is found that all these aseismic ridges except for Izu which has a thick 20-30km crust have been subducted, although many of them have formed a cusp or discontinuity at the trench. Elucidating the times of the bending of the Cretaceous-Paleogene terranes in central Honshu and in Kyushu is critical to discriminate the two models for the Shikoku Basin formation, i. e., the fixed trench model and the trench retreating model.

著者

瀬野 徹三

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.73, pp.1-25, 2020-05-10 (Released:2020-05-26)

参考文献数

143

---

Subduction off Miyagi and Fukushima prefectures, northern Honshu, has been recognized as having a triple-planed structure of seismicity at the deep thrust zone in the 40-60 km depth range. This triple seismic zone is composed of thrust-type earthquakes, down-dip compressional and down-dip tensional earthquakes from top to bottom. At the time of the 2011 Tohoku-oki earthquake, peculiar phenomena such as radiation of short-period seismic waves and pre- and after- slow slips within the asperities of M7 class earthquakes were observed over this thrust zone west of the 2011 main rupture zone. Further to the south, where the Philippine Sea plate is subducting beneath Kanto, a triple seismic zone has also been recognized particularly under southwest Ibaraki prefecture. The thrust-type earthquakes at the top of the triple seismic zone off northern Honshu and beneath Kanto have been believed to be interplate events representing the relative motion between the overriding and subducting plates. I conclude that the thrust-type earthquakes beneath southwest Ibaraki prefecture are in fact within the crust of the subducting Philippine Sea slab, not at the surface because their slip vectors are different from the relative motion between the subducting and overriding plates. Therefore, there would be an aseismic plate boundary above the seismicity. I also show that the dip angles of the westerly dipping fault planes of the thrust-type earthquakes off Miyagi prefecture are smaller by 6° in average than the dip of the slab surface in this region, except for the six years prior to the Tohoku-oki earthquake, i.e. prior to 2006. Furthermore, the slip vectors coincide with the relative motion between the overriding and subducting plates only during this period. I infer that the topmost earthquakes of the triple seismic zone off Miyagi prefecture prior to 2006 are thus likely to be within the crust of the subducting plate. The slow slips before and after the Tohoku-oki earthquake would have occurred not within the asperities but along the aseismic plate interface, and the short-period seismic waves would have been radiated due to fractures within the crust associated with the overshooting rupture at the time of the Tohoku-oki earthquake. Many of the so-called repeating earthquakes at the topmost surface of the subducting plate would be in fact intra-crustal events within the slab. M9 earthquakes would interact with the triple seismic zone, not only mechanically, but also through fluid migration, because earthquakes in the triple seismic zone involve dehydration reaction. The irregularity of the occurrence of M9 earthquakes might be due to the inhomogeneous distribution of hydrated minerals in the incoming plate. The subduction zones having M9 earthquakes or under Kanto have a collisional character. I propose to term subduction having both a collisional character and a triple seismic zone as “super-subduction”. The relative motion between the plates is accommodated by the deformations of the crust of the subducting slab as a “plate boundary zone”. The viewpoint of “super-subduction” is necessary to understand earthquakes in subduction zones with a collisional character and dehydration reactions in the slab.

著者

瀬野 徹三

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.29, no.2, pp.197-200, 1976-05-15 (Released:2010-03-11)

参考文献数

9

著者

瀬野 徹三

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.30, no.3, pp.253-264, 1977-12-05 (Released:2010-03-11)

参考文献数

18

被引用文献数

1

---

In the previous paper (SENO, 1977), the method of calculation of the recurrence time interval of great earthquakes in the Nankai and the Sagami trough regions was improved and refined. The recurrence time interval T and the value d (so-called recovery ratio) were estimated at the several sites on the seismic crustal movement areas along these troughs.In the present paper, the vertical crustal movement observed by precise levellings and the defomation of the Holocene terraces in the south Kanto district are reexamined because the deformation of the coastal terraces have some complicated relations with the seismic crustal deformations in this region.In the Shonan district, the deformation of the Holocene terraces is attributed to the crustal deformation associated with the 1923 Taisho type earthquakes and the recurrence time T of 180-400 years and the value d of 0.25-0.50 are obtained. In the southern Boso peninsula, the deformation of the Holocene terraces is divided into two: the crustal deformation associated with 1923 type earthquakes and that caused by the fault off the Boso peninsula which moved at the time of the 1703 Genroku earthquake. The recurrence time T and the value d for this fault off the Boso peninsula are estimated to be 950-2500 years and 0.20-0.54, respectively.

著者

木村 学 堤 浩之 早坂 康隆 鈴木 康弘 瀬野 徹三 嶋本 利彦 渡辺 満久 榊原 正幸

出版者

東京大学

雑誌

国際学術研究

巻号頁・発行日

1997

---

極東ロシアから日本列島に至る地域は被害地震が多発する地域である。近年これらの地震は北米・ユーラシア両プレート間の収束運動もしくはその他のいくつかのマイクロプレートが関与したプレート境界でのもの、ととらえられるようになった。相次ぐ被害地震にもかかわらず、ネオテクトニクスに関する研究はこれまで政治的・地理的・気候的制約があって進んでいない。そこで新年度に続き、極東ロシア、特にサハリン島北部地域の総合的なネオテクトニクス調査研究を実施した。具体的に以下の研究を行った。1. 航空写真による変動地形、活断層解析。特にサハリン島、中〜南部に分布、発達する活断層について変位のセンス及び変位置について解析した。2. 変動地形活断層の現地調査。特に中部及び南部サハリン。3. 地質学的調査。航空写真によって明らかになった活断層の累積変位、変位速度を明らかにするために現地で活断層露頭や、樹木成長の記録を調査した。サハリン変動帯最北部のシュミット半島にて、中生代来のオフィオライト、及び変形した堆積岩及びスレート帯について、構造解析を実施した。その結果、第三紀後期に北東南西方向の圧縮を受けて、地質体は激しく変形していることが明らかとなった。この変形様式は現在進行中の地殻変動と調和的である。従って、サハリン北部の地殻変動は第三紀以降、右横ずれの同じセンスのもが累積していることが明らかとなった。

著者

瀬野 徹三

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.61, pp.357-364, 2009

被引用文献数

2

---

History of studies of intraslab seismicity and its generation mechanisms, since the work by Wadati, is reviewed. Through the initial stage of studies of morphology of the intraslab seismicity, there followed the stage of discussion of focal mechanisms and terminal depths by mechanics and temperature of the slab. In 1970s, double seismic zones were discovered and their generation mechanisms were discussed in terms of bending or thermal stresses. In recent years, to overcome a difficulty that very high pressure prevents intraslab seismicity, dehydration embrittlement and phase transformation have been invoked for the mechanisms of intermediate and deep earthquakes, respectively. If the intermediate seismicity represents dehydration, it may give us a key to understand the distribution of fluids to the upper plate and to the seismogenic interplate thrusts, and finally to understand tectonics and volcanism in subduction zones.

著者

瀬野 徹三

出版者

公益社団法人 日本地震学会

雑誌

地震. 2輯 (ISSN:00371114)

巻号頁・発行日

vol.46, no.4, pp.461-477, 1994-03-01

参考文献数

63

被引用文献数

2 1

---

Tectonics of the Taiwan region is reviewed. Relative plate motions so far obtained are described and rated. The most reliable solution gives 7.4cm/yr Philippine Sea-Eurasian motion in the N50&deg;W direction in central Taiwan. Plate boundary geometries and modes of plate consumption in the region are discussed on the basis of geophysical, geological and geomorphological data. The major thrust zones at the Western Foothills and the Longitudinal Valley constitute mechanical plate boundaries, but a considerable fraction of the relative plate motion is also consumed by the strike-slip faulting off the southeast coast of Taiwan.<br>The cause for the occurrence of the strike-slip faulting off the southeast coast of Taiwan is discussed based on the various models so far proposed. The bending of the Philippine Sea plate due to the subduction at the Ryukyu Trench and the collision in the Longitudinal Valley are similar to the tectonics of the Izu Peninsula region in Japan, and are the most likely cause for the strike-slip faulting.<br>The reconstruction of the motion and plate boundaries in the vicinity of Taiwan for the past 4-6m. y. is reviewed. The Philippine Sea-Eurasian motion for the past 4 Ma is similar to the present one. The motion prior to 4 Ma may be more northward than present due to the absence of subduction at the Philippine Trench. The Luzon arc started to collide with the continental margin of S. E. China around 4 Ma.

著者

吉田 明夫 瀬野 徹三

出版者

特定非営利活動法人日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.37, no.6, pp.297-301, 1992-12-25

被引用文献数

4

著者

瀬野 徹三

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.116, no.3-4, pp.370-379, 2007-08-25 (Released:2009-11-12)

参考文献数

27

被引用文献数

2 2

---

I discuss the danger of earthquakes occurring directly beneath the metropolitan area from temporal and geographical viewpoints. Temporally, large (M>7) earthquakes in Kanto occur 70 years before and a few years after great interplate Kanto earthquakes. The recurrence times of such great earthquakes are more than 220 years. Because 80 years have passed since the last one, at least60 years remain before reaching the active period. It is not legitimate to calculate the probability of large earthquakes occurring in the near future, using the rate of occurrence during the active period before a great earthquake. From a geographical viewpoint, S. Kanto is located in the outer zone south of the Median Tectonic Line, where few active faults are distributed. However, in S. Kanto, exceptionally, the Tachikawa fault and the 1855 Ansei-Edo earthquake are located in the outer zone. This zone is specified by a low-velocity zone in the mantle wedge of the upper plate. Dehydration from the subducting slab may weaken the upper plate in this zone, producing anomalous intraplate earthquakes. The upper crust above this low-velocity area should be marked especially as an area having a potential for large earthquakes in the future. The probability of M7 earthquakes being generated at the interface between the Philippine Sea and the upper plates is small. Temporally, the danger of large earthquakes occurring in the near future beneath the metropolitan area does not seem to be large.

著者

瀬野 徹三 大槻 憲四郎 楊 昭雄

出版者

東京大学

雑誌

東京大學地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.75, no.1, pp.57-77, 2000

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The Chi-Chi earthquake occurred at the thrust-decollement in the accretionary prism of a young collision zone in central Taiwan. This event is thus not different from a subduction zone earthquake if Taiwan were covered by the sea water. The surface ruptures were accompanied by little damage except for the collapse of buildings standing across the surface faults. The slip directions of the surface faults were mostly NW, which is consistent with the earthquake slip vector, but there were also many W-SW and N directed slips. At the northwest corner of the earthquake fault, significant uplifts and multiple thrusts in the river bed occurred. These might all be related to the fact that the shallow portion of the earthquake fault cut the weak accretionary prism and the sediment on it. The uplifts at the northwestern corner imply an abnormal tsunami if the area were under the sea, thus suggesting a new factor for the mechanism of tsunami earthquakes: deformation of the sediment or weak accretionary prism at the lowest trench slope (Seno, 2000). The Chi-Chi earthquake might provide a unique chance to observe a subduction earthquake on land.1999年9月21日台湾中央部で起きた集集地震は,ルソン弧と中国大陸縁との間の衝突でできた付加体を切る逆断層(スラスト)で起きた.ここはユーラシアプレートとフィリピン海プレートとのプレート力学境界にあたり,通常の沈み込み帯でおきる地震と地学的には変わらない.地表で車寵埔断層として知られていた活断層に沿って地表断層が現れたが,その付近では,地表断層をまたいだ建物が壊れているのが特徴で,それ以外の被害は小さかった.地表断層のすべり方向は,かなりのものは北西方向であったが,一方西,南西,北方向のすべりもかなりの数がみられた.地表断層の北端では,大甲渓という河川の中の滝,桃畑の砂利断層崖,ダムの破損地などにおいて,弾性理論から期待できる隆起よりも3mほど大きい隆起が起きた.