著者

守屋 以智雄

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.123, no.1, pp.89-122, 2014-02-25 (Released:2014-03-07)

参考文献数

43

被引用文献数

5 5

---

The evolution of 84 volcanoes in the Philippines is outlined geomorphologically on the basis of interpretations of volcanic landforms using aerial photographs, topographic maps, satellite images, and geomorphological and geological field surveys. Fifty-six stratovolcanoes, three caldera, three lava domes, four scoria cones, four lava fields, and 10 shield volcanoes are identified. Large basaltic volcanoes such as lava fields and shield volcanoes were found unexpectedly in subduction zones. No lava field or shield volcano has been discovered on the Japanese Islands. Among the 34 subduction zones in the world, 19 do not have lava fields or shield volcanoes. Two oblique subduction zones form the Philippine Fault Zone. The fault zone mostly coincides with the eastern volcanic zone. At the southwestern part of Mindanao Island, a volcanic chain, consisting of Bulibu, Basilan, and Cagayan Sulu lava fields, Balatukan, Mangabon, Katangrad, Kalatungan, Makaturing, Bacolod, and Pagayawan shield volcanoes, and Pagadian lava domes (monogenetic volcanoes) trends northeast-southwest, in parallel with the trenches and main arcs. The association of the volcanoes with the trenches and arcs suggests that the volcanic chain is a marginal sea ridge between Sulu Sea and Celebes Sea and that the back-arc basin ridge might have extended under Mindanao Island from Moro Gulf to the northern part of Mindanao Island.

著者

長沼 佐枝 荒井 良雄

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.121, no.6, pp.1030-1042, 2012-12-25 (Released:2013-01-07)

参考文献数

24

被引用文献数

1 1

---

Seaside-Momochi, now an affluent residential area in the waterfront district of Fukuoka City, Kyusyu, Japan, was originally designed for middle-class inhabitants. This paper examines why the government of Fukuoka City changed the original concept of the residential development plan for Seaside-Momochi to cater for higher-income households. At the initial stages of the planning process in 1984, the Fukuoka City government focused on the welfare of middle-class inhabitants. However, the government found it difficult to find buyers for the land due to a decrease in housing demand among the middle class, and the project was in danger of stalling. A few years later, land prices in the city rose in the context of a property boom. This suddenly increased the development potential of the Seaside-Momochi area, and several private housing companies became interested in the Seaside-Momochi development project. However, the companies joining the project proposed modifying the original development plan to focus more on attracting affluent buyers. Despite this being a departure from its original intentions, the Fukuoka City government decided to alter the plan in order to avoid losing the development plan. The government modified the original plans and land-sale strategies. This resulted in a development plan that focused not on middle-class inhabitants but on higher income households.

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.17, no.8, pp.601, 1905-08-15 (Released:2010-12-22)

著者

早坂 一郎

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.61, no.4, pp.154-156, 1953-01-30 (Released:2009-11-12)

参考文献数

1

著者

松川 正樹

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.130, no.5, pp.653-681, 2021-10-25 (Released:2021-11-17)

参考文献数

90

---

The Tetori Group comprises significant Mesozoic (middle Jurassic–early Cretaceous) marine and terrestrial strata in East Asia. A facies analysis of the group is conducted to reveal the development of the Tetori sedimentary basin. The Tetori Group in the Mt. Hakusan Region is mainly distributed in three areas: the Kuzuryugawa Area in Fukui Prefecture and the Shiramine and Shokawa districts in the Hakusan Area in Ishikawa and Gifu prefectures. Seven lithofacies associations are recognized, which represent the deposition in talus and proximal alluvial fan, gravelly braided river and alluvial fan, sandy braided river, lacustrine delta, estuarine, shoreface, and inner shelf environments. Based on the characters and spatio-temporal distribution of these lithofacies associations across the basin in the three areas, the group is interpreted to have developed in four stages. Stage 1 is represented by the lower part of the Tetori Group in the Kuzuryugawa Area in the southern part of the basin, and shows, in ascending order, talus and proximal alluvial fans, inner shelf, shoreface, and alluvial fan facies. Stage 2 represents the lower middle part of the group in the Shokawa District in the northeastern part of the basin, and shows a change from estuarine, shoreface to inner shelf, and back to shoreface facies. Stage 3 is recognized in the middle part of the group in both the Shiramine and Shokawa districts in the northwestern and northeastern parts of the basin, respectively. Stage 3 was initially formed as talus and proximal alluvial fan, gravelly braided river and alluvial fan, and sandy braided river facies, and was later changed to lacustrine delta, sandy braided river, and gravelly braided river and alluvial fan facies, and back to lacustrine delta and sandy braided river facies in ascending order in the Shiramine District, and was initially formed as estuary and shoreface facies, and was later changed to estuary, lacustrine delta and sandy braided river facies in ascending order in the Shokawa District. Stage 4 is represented by the upper part of the group in all three areas, and shows talus and alluvial fan, gravelly braided river and alluvial fan, and sandy braided river facies. The Tetori basin reflects an upheaval of the basin forming an inter-mountain basin. This supports the hypothesis of a juxtaposition of late Jurassic to earliest Cretaceous accretionary complexes along the eastern margin of the Asia continent during the Hauterivian (Early Cretaceous).

著者

長井 雅史 小林 哲夫

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.124, no.1, pp.65-99, 2015-02-25 (Released:2015-03-11)

参考文献数

43

被引用文献数

10 11

---

Ioto (Iwo-Jima; Sulphur Island) is a volcanic island located at the volcanic front of the Izu-Bonin arc about 1250 km south of Tokyo. The island consists of a central cone and southwest rim of a submarine caldera with a diameter of about 10 km. The rocks of the volcano are trachyandesite and trachyte, which are seldom found at a volcanic front. High rates of geothermal activity and crustal uplift have been observed, which are considered to be related to magma intruding at a shallow depth. Therefore, Ioto volcano is considered to be an active resurgent dome. However, eruptive history, including the process and timing of caldera formation, has not been clarified. Eruptive history based on our recent field survey, dating, and chemical analysis is as follows. A pre-caldera edifice was formed by volcanic activity of trachyandesite-trachyte magma in a subaerial and subaqueous environment. The magma composition and types of eruption were similar to those of the post-caldera edifice. It is still unclear when the caldera was formed. The caldera floor, which was a sedimentary basin with shallow marine sediments and a subaqueous lava flow, has been present at least since 2.7 cal kBP. Furthermore, a small volcanic island covered with trees used to exist in the Motoyama area. The complicated sequence of the Motoyama 2.7 cal kBP eruption is described as follows. First, on the volcanic island or in the surrounding shallow water, an explosive phreatomagmatic eruption occurred that formed subaqueous welded tuff (Hinodehama ignimbrite) and a subsequent thick subaqueous lava flow (Motoyama lava). While the Motoyama lava was still hot, the eastern part collapsed. The collapsed mass was quenched to form large blocks similar to pillow lava. A subsequent large phreatomagmatic eruption occurred, destroying the hot Motoyama lava, the older edifice, and the marine sediment. The resultant subaqueous pyroclastic flow generated the Motoyama pyroclastic deposit. Then, the eruption center shifted to the Suribachiyama area, which is just outside the southwest caldera rim. Deposits from three different eruption periods have been identified—lower, middle, and upper pyroclastic deposits—and a lava flow that erupted during the middle pyroclastic period. The lower unit was formed by a subaqueous eruption at a deeper level; the middle deposit was formed by a phreatomagmatic explosion at a shallow depth; and, the following lava emission generated a lava island. The upper pyroclastic deposit was generated by a combination of phreatomagmatic and Strombolian eruptions. Although the ages of these eruptions are not obvious, the first phase of the eruption occurred during the period between 2.7 cal kBP and 0.8-0.5 kBP, which is estimated from the age of the upper marine terrace X (Kaizuka et al., 1983). The eruption of the upper deposit occurred before AD 1779 (ca. 0.2 kBP). The eruptive products described so far are covered with younger sediment from marine terraces and spits. Recently, small-scale deposits from phreatic explosions accompanied by geothermal and uplift activities have been found distributed throughout the island, but juvenile material has not been confirmed to exist in the products.

著者

片山 郁夫 平内 健一 中島 淳一

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.119, no.2, pp.205-223, 2010-04-25 (Released:2010-07-06)

参考文献数

70

被引用文献数

6 8 2

---

Water is known to play important roles in earthquake generation and volcanic activity. Consequently, the presence of water and its heterogeneous distribution in subduction zones may contribute to the variability of subduction seismicity and arc magmatism. In this study, we infer water distribution, including aqueous fluids and hydrous minerals, based on the seismic tomography beneath Japan, and discuss subduction processes in terms of water circulation in subduction zones. Two distinct oceanic plates, the Pacific plate and Philippine Sea plate, are subducting beneath Japan. These plates have quite different characteristics. The Pacific plate is old (∼130 Ma) and is subducting beneath northeast Japan as rapidly as 10 cm/year. In contrast, the Philippine Sea plate is relatively young (∼20-50 Ma) and is subducting at ∼3-5 cm/year beneath southwest Japan. The subducting old Pacific plate results in cold environments beneath northeast Japan, whereas the thermal structure beneath southwest Japan is relatively warm as a result of the young Philippine Sea plate subduction. Most water is released by eclogite transformation in the subducting oceanic crust, and the expelled water infiltrates into the mantle wedge, forming hydrous minerals such as serpentine and chlorite. The seismic tomography beneath northeast Japan shows that eclogite transformation occurs at depths of ∼80-100 km, and above these depths, a low-velocity anomaly and high Vp/Vs are detected in the mantle wedge. In southwest Japan, eclogite transformation occurs at much shallower depths (50-60 km) due to a warm subduction geotherm. The down-dip limit of interplate seismicity is likely to be controlled by a brittle-ductile transition in southwest Japan, whereas such a limit beneath northeast Japan coincides with the low-velocity anomaly at depths of 60-70 km, suggesting that the presence of serpentine inhibits earthquake activity at the plate interface. The double plane of intraplate seismicity is probably caused by dehydration of eclogite forming reactions in the upper plane and serpentine/chlorite dehydration in the lower plane, although seismic activity is absent at the mantle wedge where water is released by serpentine breakdown. Low-frequency tremors above the Philippine Sea plate are mostly located at the interface between island arc Moho and subducting plate surface. Abundant aqueous fluids in this region due to permeability contrasts may trigger low-frequency tremors. A slab parallel low-velocity zone beneath northeast Japan is interpreted as a melt-filled upwelling flow in the mantle wedge. Such an anomaly is not detected in southwest Japan, and slab melting of the subducting Philippine Sea plate is probably the source of the arc magmatism in this region.

著者

今岡 照喜 永嶌 真理子

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.131, no.2, pp.235-256, 2022-04-25 (Released:2022-05-13)

参考文献数

98

被引用文献数

3

---

The mineralogical characteristics of metasomatic Li-minerals in Iwagi Islet, sugilite, katayamalite, murakamiite, Li-rich pectolite, zektzerite, sogdianite and taeniolite are summarized. These Li-minerals occur in metasomatic albitite, which contains 500 ppm Li. Such a high-Li albitite content is unusual amongst metasomatic rocks in Setouchi Province of SW Japan. Albitite forms small bodies that are several tens of centimeters to tens of meters in size, and are disseminated in a host granite of Late Cretaceous age. It shows conspicuous strain-induced textures. Murakamiite and Li-rich pectolite form a solid solution with Li × 100/(Li + Na) atomic ratios ranging from 44.2 to 60.1, and Na line profiles show a zoning structure in which Na decreases from core to rim. Albitite-normalized element concentrations vary systematically with the ionic radius of the element; normalized concentrations of cations with the same valence roughly form a simple convex parabolic curve when plotted against the ionic radius. This indicates that the element partitioning of murakamiite and pectolite during metasomatism to form albitite took place under the strong control of a crystal structure, quasi-equilibrated with metasomatic fluids and coexisting minerals. The δ7Li values of murakamiite and Li-rich pectolite show a wide range from −9.1 to +0.4‰ (average −2.9‰), and no obvious correlation with Li content is observed. These δ7Li values should have resulted from hydrothermal fluid–rock interactions at temperatures of 300-600°C (hydrothermal stages). The very low δ7Li values down to −9.1‰ may have originated from intra-crystalline Li isotope diffusion, or involvement of deep-seated, Li–Na-enriched subduction-zone fluids with low δ7Li values. The occurrence of porous zircon, dalyite, and mantles of zektzerite and/or sogdianite on resorbed zircon in albitite suggests that those zirconium silicate minerals are the products of metasomatic mineral replacement reactions by dissolution–reprecipitation processes associated with Na-, K-, and Li-rich hydrothermal fluids.

著者

圦本 尚義

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.131, no.2, pp.163-177, 2022-04-25 (Released:2022-05-13)

参考文献数

71

被引用文献数

2

---

Determining the elemental abundances of the Earth is one of the fundamental interests of the Earth and planetary sciences. The elemental abundances of the bulk solar system, chondrites and bulk Earth are reviewed. The elemental abundances of the bulk solar system resemble those of chondrites, with the exception of atmophile elements. CI chondrite may be most resemblant, but significant improvements in solar photosphere spectroscopy are necessary to reject other chondrites. Volatilities of elements control chemical variations among chondrites. These variations may reflect global thermal structures in the proto-solar disk. Alternatively, the variations may correspond to accretion ratios of chondrite-forming components, which are refractory inclusions, chondrules, and matrix, into the parent bodies. The elemental abundances of bulk silicate Earth can be empirically estimated without referring those of the bulk solar system and chondrites if we use chemical variations of mantle rocks. However, the chemical composition of bulk Earth remains largely uncertain because it is difficult to estimate the chemical compositions of the central core and the lower mantle without formation models of the Earth.

著者

阿部 和俊

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.123, no.2, pp.315-322, 2014-04-25 (Released:2014-05-16)

参考文献数

8

被引用文献数

6 4

---

This paper evaluates the status of Tokyo among major cities of Japan and compares Tokyo with major cities of the world in terms of head and branch offices. First, the paper analyzes major cities of Japan from the standpoint of the head offices and branch offices of large private firms. The main focus of this analysis of Japan is the period from 1950 to 2010. Clearly, the largest number of head offices is found in Tokyo. This is followed by Osaka. However, it should be noted that in recent years, more and more firms have adopted the system of having multiple head offices. Including such firms, the number of private firms with head offices in Tokyo is steadily increasing. Tokyo houses the large number of branch offices, as well. As is the case for head offices, the city with the second largest number of branch offices is Osaka. The difference in status between Tokyo and other cities, particularly Osaka, has increased in recent times. The status of Tokyo has become more elevated with Osaka losing ground. Second, the paper compares the situation in Tokyo with major cities of Korea, France, the United Kingdom, Thailand, The United States of America, Germany, and India. Tokyo, Seoul, Paris, Bangkok, and London gravitate to the same category in that these capital cities are strong in terms of office locations. On the other hand, within The United States of America, Germany, and India, capital cities are not so strong in terms of numbers. The important factor affecting these results is the political system. Namely, in the cases of federated states, the status of capital cities is not as high. On the other hand, in the cases of non-federated states, the status of capital cities is very high.

著者

星埜 由尚

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.129, no.2, pp.227-240, 2020-04-25 (Released:2020-05-12)

参考文献数

23

被引用文献数

5 4

---

The map of Japan drafted by Inoh Tadataka is considered to be the earliest produced from a scientific survey. The descriptions of longitude and latitude are based on astronomical observations, and Inoh's nationwide survey has been considered to be the origin of modern surveys in Japan. However, he did not succeed in determining longitude. Although he had knowledge of a spherical earth, the results of his survey were projected on a plane, not on a spherical surface. The parallels of latitude drawn on his maps are based on an accurate astronomical survey he carried out, but the meridians on his maps are absolutely inconsistent. His survey method also combined traverse and intersection surveys without control points. Therefore, his nationwide survey cannot be considered to be representative of a survey carried out in the modern period. There are many open traverse lines on his maps. These lines generally extend to temples and shrines, although they are not effective for improving the accuracy of the survey. Because temples and shrines might have been important public facilities at that time, the Tokugawa shogunate government probably requested information concerning their locations. He carried out a nationwide survey ten times, but he could not survey the northern half of Ezo island (Hokkaido). It is said that Mamiya Rinzo, who studied survey technology under Inoh Tadataka, surveyed Ezo island and submitted his survey data to Inoh Tadataka, therefore, Inoh's map of Ezo island might be entirely based on Mamiya's data. Further studies are necessary because Mamiya's survey has not been clarified.

著者

横山 又次郎

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.7, no.11, pp.596-598, 1895-11-10 (Released:2010-10-13)

著者

高木 菊三郎

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.52, no.12, pp.577-588, 1940-12-15 (Released:2010-10-13)

被引用文献数

1 1

著者

神保 小虎

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.2, no.3, pp.116-121, 1890-03-25 (Released:2010-10-13)

著者

大崎 晃

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.119, no.4, pp.615-631, 2010-08-25 (Released:2010-11-08)

参考文献数

43

---

This study examines the American whaling industry, which was based in New England and dominated most of the Western oil market in the 18th and 19th centuries. Previous studies by the author examined why the industry was attracted to this region, highlighting the favorable economic environment of the area, which allowed investors to accumulate the necessary funds to launch whaling ventures. Each investment consortium that provided funds to whaling vessels organized limited partnerships with individual vessels. This enabled consortiums to collect funds from a variety of stakeholders other than just businessmen involved in whaling and their families. Crewmembers of the vessel, reflecting the multi-racial society of the United States, were also free to select employers without relying on a conventional employer-employee relationship. Taken together, these factors led to New England attracting funds and labor from both within the region and further afield, and developing into the whaling center of the United States. An additional reason for New England's development as a whaling base was the global expansion of the industry to cover the Atlantic, Pacific, and Indian oceans, with only the Southern Ocean not affected by this growth. Crewmembers were also paid from a ship's profits using the lay system. This payment by piece ratio ensured a minimum payment to crewmembers while guaranteeing a return for investors. The hiring of native islanders as part-time laborers in the whalers' areas of operation also kept expenditure to a minimum, with all of these factors contributing to investors' profits. Against this background, the whaling industry prospered and profited up until the 1850s. In the 1870s, however, the industry started to decline as whale resources decreased and the price of whale oil fell as a result of increased petroleum production. This study examines the details of how whaling voyages were managed during this period and how New England's whaling industry underwent a rapid transformation into a mechanized cotton industry with the owners of whaling vessels switching their investments to the cotton industry at New Bedford, the center of the whaling industry in New England. The rapid change from industrial whaling to the mechanical cotton industry in New England was made possible with the abundant funds accumulated by the whaling industry. The reestablishment of consortiums progressed smoothly as limited partnerships already existed and the labor market adapted efficiently from supplying whaling vessels to supplying female workers for the cotton industry due to the presence of non-conventional employment rules. We can see, therefore, in this region the development from one industry to another was controlled only by market-based mechanisms of American management. This is in sharp contrast to the Japanese fishing industry, which developed from a manufacturing fishery through technological innovation and utilizing community manpower or industrial power as the only motive force under limited investment and labor market conditions.

著者

海野 進

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.103, no.5, pp.498-521, 1994-10-25 (Released:2009-11-12)

参考文献数

65

被引用文献数

1 1

---

Recent progress in studies on magma plubming system beneath mid-ocean ridges is reviewed. Mid-ocean ridges are not continuous, homogeneous series of crests, but are segmented by various topographical offsets of several orders of magnitude. Such topographical ridge segmentation is a surface manifestation of along-strike variations in the pattern of mantle convection and the supply of magma.Upwelling of the mantle material beneath the spreading center takes the form of a diapir, rather than sheet-like flow. Such diapiric upwelling has an along-axis dimension of several hundred to several tens of kilometers, which corresponds to first-and second-order segments, but some are as small as the scale of third-order segments. Where magma upwelling is intense, hot lithosphere and high magmatic productivity produces thick crusts, resulting in low gravity anomaly.When the spreading rate is low, mantle flow is cooled on route to the bottom of the lithosphere and ceases to melt at depths. Thus magmas produced beneath slow spreading ridges have low degrees of melting. On the contrary, fast spreading ridges are followed by intense mantle upwelling which melts significantly the mantle column from deeper part of the upper mantle up to just beneath the crust.Magmatic budget is so large at fast spreading ridges as to maintain large, steady-state magma chambers along the ridge axes with extensions comparable to second-and third-order segments. Such magma chambers have a very small melt pocket one to two kilometers wide and up to several hundred meters thick, underlain by a large mush of crystals and melt. Cumulate layers on the top of the mush sink and deform to S-shaped or downwarping layers as seen in large layered plutonic bodies in some ophiolites. However, low spreading ridges do not have enough supply of magma but only possess short-lived small magma chambers consisting of crystal mush.Volcanic landforms consist of major topographic features associated with small volcanic edifices : the former is a large shieled volcano several tens of kilometers long and is probably formed by episodic eruptions every several tens of thousand years ; the latter is a small conical lava cone comprising pillow flows which is constructed during a short-period eruption but some are active as long as 1.8 million years which are unequivocally central volcanoes.Rifting episodes at spreading axes depend on the spreading rate and the width of the volcanic zone. Slow spreading ridges such as Iceland have rifting every 100 years, but fast spreading ridges such as East Pacific Rise rift every year or two. Such rifting episodes continue for several years and are associated with multiple dikes with an injection interval of a month up to a year.Diapiric mantle upwelling, structure of magma chambers and volcanic landforms seen in mid-ocean ridges resemble those in some large ophiolites such as the Troodos, Cyprus and the Semail, Oman, and post-Teritary volcanism in Iceland.

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

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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

笠原 順三 佐藤 利典

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.106, no.4, pp.557-566, 1997-08-25 (Released:2009-11-12)

参考文献数

17

被引用文献数

2

---

The 1995 Amami-Oshima-Kinkai Earthquake occurred near the Nansei-Shoto Trench where the upheaval area of the Philippines Sea plate subducts beneath the Nansei-Shoto islands. The main shock was MJMA 6.6 and its largest aftershock was MJMA 6.5. The aftershock distribution for these two events by Yamada et al. (1996) corresponds to two distinct and nearly vertical fault zones. The focal mechanisms obtained by Kikuchi (1996) are consistent to the aftershock distribution.The authors propose that the seamount found beneath the trench-continental-slope indirectly triggered this earthquake activity. If a subducting oceanic plate is normal oceanic denser than an overriding island arc, the oceanic plate should be faulted near vertically priori to the plate subduction by horizontally tensional force due to plat bending. On the other hand, an oceanic plate with seamounts or an oceanic plateau lighter than a normal oceanic plate, might resist to plate subduction due to its small density and delaying normal faultings might occur in the subducting oceanic plate. The delaying normal faultings between a subducting seamount and a preceding normal portion of the oceanic plate can compensate the subduction process. The compressional convergence margin such as the Nankai Trough, however, may not generate such normal faultings due to the nature of stress field.The low seismicity area existing across the trench axis is also seen both in this aftershock activity and ISC hypocenters. This is the same result as those in other regions. This might imply low earthquake potential for this portion of plate interface due to the existence of low density sediments and water contained in the sediments.

著者

林 慶一

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.105, no.6, pp.723-727, 1996-12-25 (Released:2009-11-12)

被引用文献数

1 2

著者

日本地学史編纂委員会 東京地学協会

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.110, no.3, pp.362-392, 2001-06-25 (Released:2010-04-23)

参考文献数

132

被引用文献数

2 2