著者

三雲 健

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.99, no.1, pp.18-31, 1990-02-25 (Released:2010-11-18)

参考文献数

58

被引用文献数

3 4

---

Extensive studies on seismic activity and focal mechanism of major to moderate-size earthquakes that occurred along the eastern margin of the Japan Sea and the northern part of the Fossa Magna regions are reviewed and discussed in relation to regional tectonics. The validity of a prevailing hypothesis is also tested from various observations to see if the Northeast Honshu arc is part of the North American plate.Seismicity along the Japan Sea coastal regions extends southwestwards across the Toyama trough in one way, and also in other way to the northern Fossa Magna through a zone near the Shinano river. It has been noticed that the seismicity show temporarily successive properties similar to migration phenomena. Five major earthquakes along the Japan Sea regions have been interpreted as having thrust-type mechanisms, and the depth distribution of aftershocks of two larger events and the dip of submarine active faults suggest an eastward dipping fault plane.The maximum compressive stress derived from the focal mechanisms of more moderatesize earthquakes indicates E-W to ESE-WNW orientations, changing gradually from the northern to southwestern part of the coastal regions. In inland regions west of the northern Fossa Magna, the general trend appears oriented again in the ESE-WNW direction, which is found to be well consistent with the direction of principal compressive strains derived from geodetic triangulation surveys over the last 80 years.All the above evidence suggests that the regions under consideration may be a tectonically active, convergent zone, and might be regarded as a zone of a possible plate boundary. There is no direct evidence, however, suggesting an eastward incipient subduction of the Japan Sea lithospheric plate, from observations of submarine topography and upper crustal structure beneath the regions.Numerical calculations show that the suggested hypothesis could partly account for the observed directions of compressive stress in Northeast Honshu but is apparently inconsistent with those in Southwest Honshu. The results suggest that the Northeast Honshu arc may better be regarded as a “micro-plate” which receives strong compressive stress not only from the westward movement of the Pacific plate but also from the west side. One of possible sources of the driving stress from the west side might be an eastward movement of the “Amurian plate” which is one of micro-plates detached from the Eurasian plate. Another possible source could be bilateral extension of the central Japan Sea region or of the regions covering Northeast China and the Korean peninsula.

著者

早津 賢二

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.102, no.5, pp.611-613, 1993-10-25 (Released:2009-11-12)

参考文献数

10

著者

長岡 信治 古山 勝彦

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.113, no.3, pp.349-382, 2004-04-25 (Released:2009-11-12)

参考文献数

32

被引用文献数

5 9

---

Many basaltic monogenetic volcanoes forming groups are distributed on Fukue Island, the largest island of the Goto Islands. The Onidake volcano group, 8×10 km across, is one of the monogenetic volcano groups in the island. It contains eleven monogenetic volcanoes, namely, Daienji, Koba, Nagate, Masuda, Shimosakiyama, Hinodake, Kamiozu, Shirodake, Sakiyamabana, Midake-Usudake, and Onidake, in chronological order. K-Ar and 14C dating results show that these volcanoes were active during 0.5-0.018 Ma. The average interval of monogenetic volcano-forming eruption is fifty thousand to thirty thousand years, while a long interval of about one hundred thousand years exists between 0.25 and 0.15 Ma. By long interval, the group is divided into older volcanoes, Daienji, Koba, Nagate, and Masuda, and younger volcanoes, Shimosakiyama, Hinodake, Kamiozu, Shirodake, Sakiyamabana, Midake-Usudake, and Onidake.At about 0.42 Ma, the activities of the older volcanoes started with Daienji volcano, which produced a lava flow in the north area. It was covered by thick lava flows of Koba volcano at about 0.38 Ma. During or shortly after the activity of Koba volcano, Nagate shield volcano with two small scoria cones became active in the northeastern area. At about 0.30 Ma, in the western area, Masuda volcano erupted to form a lava plateau and two scoria cones.After 0.15 Ma, in the central area, the intermittent activities of younger volcanoes began with lava flows from Shimosakiyama volcano, which was covered soon by Hinodake volcano composed of three lava flows and one scoria cone. Two small cinder cones with a lava flow, Shirodake and Kamiozu volcanoes, erupted on the northern part of Hinodake volcano. At about 0.03 Ma, at the southeastern end, Midake-Usudake volcano, erupted with three cindercone-forming scoria falls and five small plateau-forming lava flows covering an undated scoria cone, Sakiyamabana.At 0.018 Ma, the latest eruption of the group, Onidake volcano, commenced in the central area, the first phase of which was the Abunze lava flow originating from welded scoria falls or a mixture of lava and scoria fall into the lava ponds in craters. Simultaneously, the scoria falls generating Abunze lava flow contributed the formation of Osako scoria cone, which partially collapsed shortly afterwards, probably because Abunze lava carried the parts away. In the second phase, Onidake scoria falls covered a large area of 5×5 km, while Onidake scoria cone was formed in the proximal area. The third phase consisted of five lava flows, Ohma lava 1, 2, and 3 and Onidake lava 1 and 2, all of which erupted from two summit craters of Onidake cone and covered the northern and western foothills of the volcano.

著者

藤岡 換太郎

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.97, no.1, pp.39-50, 1988-02-25 (Released:2009-11-12)

参考文献数

59

被引用文献数

1 2

---

Topographic features around Izu Oshima region were summarized with special references to the characteristics relating to subduction of the Philippine Sea plate (PHS) along the Sagami Trough. Several topographic highs having circular contours around Oshima Island may be the results of parasitic eruption of Oshima Volcano. Their trend is almost parallel to the elongation of the linearity of parasitic cones distributing onshore. Along the eastern trench slope off Oshima Island, large scale collapse structures are seen in the submarine topographic map. These are the result of the falling down mostly of pyroclastic materials (tephras) during historic ages. The Oshima Island shows eastward tilting owing to the bending resulted from the subduction of the PHS. Large scale of the collapse structures may be caused by the oversteepening of the eastern trench slope of Oshima Island and soft sediments consisting mostly of pyroclastics including a large quantity of pore water slide down along the trench slope as far as the Sagami Trough.Radial distribution both of saddles and valleys observed northeastern offshore part of the Oshima Island may be lava flows and/or dike swarms derived from the old Okata Volcano whose eruption center was estimated to exist at the northeastern extension of the Oshima Island.About 4 km south off the Oshima Island, large scale of the topographic breakes consisting of caotic highs and depressions are seen in the submarine topographic map. These may be debris flow deposits along eastern slope of Ohmurodashi which consists mostly of the Quaternary rhyolites geologically and chemically similar to those exposed on the Niijima and Kozushima Islands. These are the results of catastrophic phreatomagmatic eruption of the Ohmurodashi such as that of the Myojinsho. Mixture of pyroclastics and lavas will be found from these caotic areas.The upper steam of the Sagami trough shows notable meandering whose direction is almost parallel to that of the movement of the PHS east off Oshima Island and almost perpendicular east off Ohmurodashi. At the latter case, thrust structures may trace along the subduction zone at the landward slope of the Sagami trough. Just landward side of the thrust, curious round topographic highs can be observed. They may be mud volcanoes.Topographic features observed around Oshima Island may best be understood in term of the normal and oblique subduction of the Philippine Sea plate along the Sagami Trough.

著者

鵜川 元雄 藤田 英輔 熊谷 貞治

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.111, no.2, pp.277-286, 2002-04-25 (Released:2009-11-12)

参考文献数

13

被引用文献数

6 12

---

Continuous seismic observations at Iwo-jima, an active volcanic island belonging to the Izu-Ogasawara island arc, have detected remote triggering of microearthquakes in and around the island. The remote triggering at Iwo-jima is a phenomenon of an abrupt increase of microearthquake activity at the time of a passage of seismic waves from a distant large earthquake. We examined seismograms of a total of 21 earthquakes with magnitude larger than 7 and within an epicenter distance of 3000 km from Iwo-jima. Remote triggering phenomena were found at four events during the period from 1980 to 1993 : the 1983 west off Tohoku earthquake, the 1984 southeast off Kyushu earthquake, the 1993 southeast off Hokkaido earthquake, and the 1993 Mariana Island earthquake. The largest epicenter distance among them was 2009 km. The initial times of triggering coincide with the theoretical arrival times of surface waves and successive occurrences of earthquakes continued for 6 to 15 min, suggesting that dynamic stress or strain caused the remote triggering phenomena at Iwo-jima. As a well-developed hydrothermal system is suggested in shallow depths beneath Iwo-jima, volcanic fluids presumably play an important role in remote triggering.

著者

岡田 篤正 安藤 雅孝 佃 為成

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.96, no.2, pp.81-97, 1987-04-25 (Released:2010-02-25)

参考文献数

35

被引用文献数

6 2

---

Four trenches (Trenches A-D) were explored across the Yasutomi fault (a strand of the Yamasaki fault system) to date recent past faultings. Trench A was 3 m deep and 28 m long across the fault (Upper in Fig. 3 and Fig. 4), and the additional excavation was made down to 5 m deep (Fig. 5) from the western wall of trench A. The sizes of other tenches are similar to that of trench A. Since this site was being developed after this trenching for the building lot of a factory, many pieces of important geological evidence were gradually exposed with progress of the construction. This enabled us to make a further detailed geological and geomorphological study of the Yasutomi fault. The results are summarized as follows : 1) Yasutomi fault, which has been considered to be predominantly left-slip active one estimated from tectonic morphologies, was geologically confirmed that this had dislocated with predominantly lateral-slip component at least since a few tens of thousand years.2) Widely sheared zones appeared along the north side of the active trace do not accompany any tectonic features. Therefore, this straightly trending depressional zone is to be recognized as a fault-line valley. A new fault was originated along the southern rim of pre-existed weak zone probably since the late Quaternary.3) The valley-filling deposits are disturbed at the lower part of the trench but not at the upper part this suggests that the fault has not moved since the deposition of the upper horizon although small earthquakes have been reported to occur frequently around the fault. Sense and amount of vertical offset, drugged structure and other fault features vary laterally along this, as common in high angle strike-slip fault.4) The latest displacement occurred between late 7 th and 12 th Centuries, probably associated with the 868 Harima Earthquake (M=7.1). Two more faultings were also inferred from C-14 dates of disturbed and undisturbed strata within a deformed zone of the fault, although they are less reliable. The recurrence interval of earthquakes as large as the 868 event is estimated to be at least 1000 or possibly a few thousand years along this strand of the Yamasaki fault system.

著者

田中 和広 石原 朋和

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.118, no.3, pp.499-510, 2009-07-07

被引用文献数

5 10

---

The Nabetachiyama Tunnel 9116 m long was excavated in Tokamachi City, Niigata Prefecture and encountered the serious difficulties during excavation. In particular, a 600 m long section in the Matsudai area had experienced difficulties caused by swelling mudstone in the Tertiary Sugawa Formation. A 120 m bore hole long was excavated in the neighborhood of the section and geological and geochemical examinations of sampled cores were carried out to investigate the formation mechanism of the swelling rock mass. Mudstone distributed deeper than 50 m in the bore hole can be correlated to the tunnel troubled section geologically and geochemically. The section is assumed to be composed of mud breccia with mudstone fragments and clayey matrix, which is thought to be generated by hydro-fracturing of mudstone, showing weak strength due to large quantities of clay minerals. A gas pressure of 1.6 MPa thought to be caused by degassing of methane was measured during tunnel construction, which would increase the swelling properties. Mud breccia distributed deeper than 50 m contains a lot of Na-smectite formed in highly saline pore water ascending from deep underground. The result of slaking test showed that mud breccia filled with saline groundwater is characterized by quick slaking and swelling due to the marked contraction of Na-smectite when drying. In summary, the swelling rock mass distributed in the troubled section was formed by the weak rock strength caused by hydro-fracturing and high gaseous pressure generated by degassing. Furthermore, quick slaking caused by repeated wetting and drying was another reason for swelling during excavation.

著者

大和 広明 三上 岳彦 高橋 日出男

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.120, no.2, pp.325-340, 2011-04-25

参考文献数

12

被引用文献数

3 18

---

We analyze the influence of sea breeze on temperature distribution in the Kanto Plain (central Japan) on a day that a sea breeze front was detected (known as sea-breeze front days) using high-resolution temperature data observed by our research team.<br> The high-temperature area on sea breeze front days moves northwest from central Tokyo, and was located at Kawagoe city (middle Kanto Plain) at 14 JST, and the northern Kanto Plain at 16 to 18 JST, respectively. This high-temperature area appears at the head of the sea breeze front to the leeward of central Tokyo, where the daily maximum temperature is highest in Kawagoe city and the northern Kanto Plain. After the sea breeze front passes, the area where the temperature is higher than that at the circumference is distributed in the shape of a wedge. This wedge-shaped area is located to the leeward of central Tokyo where the wind from Tokyo Bay and Sagami Bay forms a convergence zone. The high-temperature area around Kawagoe city, which cannot be found on days with strong winds, is formed from the hindrance of cold air advection caused by sea breeze front penetration.<br> On the other hand, high temperatures in the northern Kanto Plain may not be related to the penetration of sea breeze fronts, which do not reach the northern Kanto Plain on days when the daily maximum temperature is recorded. However, the temperature in the northern Kanto Plain is higher on sea breeze days than on strong southerly wind days, and this suggests that local circulation plays an important role in causing high temperatures in the northern Kanto.

著者

小泉 格

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.116, no.1, pp.62-78, 2007-02-25

被引用文献数

3 8

---

The results of hydro-environment researches into marine and lacustrine sediments revealed climatic variations which seem to have some relationships between turns in world history and climatic changes. In the Japan Sea and northeast Pacific off Kashima from the Late Glacial to the Holocene, diatom temperature, <I>Td</I>' = (frequency of warm-water species) - (frequency of warm-and cold-water species) <SUP>-1</SUP>?100, values show rhythmic fluctuations with durations of 1 kyr and 400-500 yrs (Koizumi et al., 2004, 2006). This indicates a strong and regular inflow of the warm Tsushima Current into the Japan Sea as a branch of the warm Kuroshio Current. The decreases of <I>Td</I>' values correspond to a period of climatic deterioration under which cultural changes occurred in Japan. The paleoclimatic variations and the triple events of high <SUP>14</SUP>C in the atmospheric residual <SUP>14</SUP>C record denoted by Stuiver <I>et al</I>. (1991) are recognized in the diatom variations.<BR>A similar periodicity is also recognized in North Atlantic drift ice (Bond <I>et al</I>., 2001), concentrations of sea salt and terrestrial dust in the GISP2 ice core (O'Brien <I>et al</I>., 1995), in lake deposits from the Jura in France (Magny, 1995), Tibet (Gasse et al., 1991; Ji <I>et al</I>., 2005), and Alaska (Hu <I>et al</I>., 2003), and oxygen isotope variations from stalagmites in southern China (Wang <I>et al</I>., 2005) and Oman (Neff <I>et al</I>., 2001).<BR>Climatic deteriorations are synchronous with periods when serious changes occurred in human intellectual achievements during the Holocene. The Agricultural Revolution (11, 000-10, 000yr BC), with the cultivation of wild plants and domestication of wild animals to produce and secure food, seems to coincide with the Younger Dryas event. Increased agricultural production made it possible to afford a population not engaged in agriculture, for example, people engaged in handicrafts, festivals, and politics. This seems to occur in the period coinciding with T<SUB>2</SUB> event in the T<SUB>1</SUB>-T<SUB>4</SUB> triplets, which have Maunder-and Sporer-type patterns occurring in sets of three, denoted by Stuiver and Braziunas (1993). The religious courtesy belief in the recycling and the reinforcing of life was converted into a rational and systematic consideration of life based on universal theory. This conversion of thinking seems to coincide with the T<SUB>3</SUB> event. Modern science was established in Europe in the 17th century. And now human beings are destroying natural environments using highly developed scientific technologies of their own. This is a negative revolution that human beings have never previously experienced.<BR>In the south-to-north transect of the cores from both the Pacific and Japan Sea sides of Honshu, <I>Td</I>' values indicate that the Kuroshio Current and Tsushima Warm Current are both weakening at present. The present interglacial period might end and become a cooler climatic condition like a Little Ice Age within 300 years. The insolation at 37°N among the Earth's orbital parameters is weak at present (Koizumi and Ikeda, 1997). However, the mean global temperature has risen about 0.5°C during the last century. Warming of the Earth, which is caused mainly by carbon dioxide in the atmosphere, has made natural environments unstable.

著者

柳井 修一 青木 一勝 赤堀 良光

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.119, no.6, pp.1079-1124, 2010-12-25

被引用文献数

8 64

---

Median Tectonic Line (MTL) and Fossa Magna (Itoigawa-Shizuoka Tectonic Line) had long been considered to be the most critical fault boundaries controlling development of the Japanese Islands since Naumann (1885) and Kobayashi (1941). After the appearance of plate tectonics, several new interpretations emerged, <i>e.g.</i>, sub-surface Benioff plane for the MTL. In this paper, we propose that those tectonic lines, major faults, and Tanakura Tectonic Line (TTL) were formed through a process at micro-plate boundaries during the opening of the Japan Sea in the Miocene.<br> MTL could have been formed along the consuming boundary between the PHS plate and Japan Sea microplate, which has shifted southward to the Nankai trough, accompanying large-scale tectonic erosion. Fossa Magna was formed as a gigantic transform fault with a transtension component in the Medial-Japan Sea when opening was initiated. The eastern and western boundaries of the Japan Sea must be a strike-slip fault, corresponding to TTL to the east, and a newly proposed strike-slip fault called the West Kyushu Tectonic Line, respectively. Fossa Magna, a medial region defined by two NS-trending Miocene parallel faults in central Honshu, defined by Nauman (1885) could be interpreted to be the largest transform fault in the Medial-Japan Sea to offset the spreading axis when the Japan Sea opened.<br> It should be emphasized that large-scale tectonic erosion occurred in front of consuming plate boundaries facing the PHS and PAC plates oceanward during the opening of the Japan Sea. The volume of tectonic erosion is calculated to be 17,581,500 km³, which is equivalent to 2/3 of the present-day Japan arc crust, which is sufficient to reach the depth of the megalith between the upper and lower mantle boundary, even with 10 km thickness of materials eroded and transported along the Benioff zone.<br> Although MTL, Fossa Magna, and TTL are remarkable in the geology of Japan, these young faults never affected the orogeneses of Japan back to 520 Ma, which grew the continental crust of Japan. We propose that microplate boundary processes decreased the volume of the Japan crust.

著者

矢島 道子

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.120, no.1, pp.237-238, 2011

著者

伊神 輝

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.99, no.1, pp.61-71, 1990-02-25 (Released:2010-11-18)

参考文献数

40

---

Newly developed idea of the nascent plate boundary along the eastern Japan Sea has become to be discussed in the last five years. The boundary extends southwards through central Japan, where the Itoigawa-Shizuoka Tectonic Line (ISTL), one of the great tectonic lines in Japan, traverses to Suruga Bay. In the south of central Japan, the Philippine Sea plate is subducting under Japanese Islands, which lie on the North American plate and the Eurasia plate, and, therefore, a triple junction is formed there, if we acceptthe new idea of the plate boundary. Central Japan is, then, considered to be situated under the complex tectonic stress fields due to the plate interactions, and has the structures resulting from ongoing or past geodynamical process.Many seismic probings have been undertaken in central Japan and the derived structure will open informations on the geodynamic process and verifications of the nascent boundary. New resolution methods in seismic probing of the crust and the upper mantle can derive a three-dimensional velocity structure. The derived structure in central Japan, including ISTL, shows a low velocity body beneath the Hida mountains at the east of ISTL. However, the difference between the North American plate and the Eurasia plate has not beenresolved over the whole area along ISTL from the P-wave velocity of viewpoint. Many explosion profiles have been conducted in central Japan, some of which cross ISTL. The result at the north of ISTL shows a distinctive reverse fault dipping east near the Matsumoto Basin, though the fault location is slightly different eastwards from the geologically estimated tectonic line. The dip of the fault is concordant to that derived from the newidea of subducting the Eurasia plate under the North American plate. We cannot find other seismic profiles showing the similar structure in this area. In the southern part of ISTL, the northsouth fault is derived, which may be deformed by the plate interaction between thePhilippine Sea plate and the Eurasia plate.Unraveling a highly and widely resolved structure will be required to step forward to verify the new plate boundary hypothesis, and to put it practice, it is necessary to develop observation systems as well as the processing techniques. We address a request ofdeep seismic sounding which has controlled sources on a long-range profile with seismic waves penetrating deep into the crust and the upper mantle on a scale to discusss the new plate boundary hypothesis. Almost simultaneously, seismic tomography using natural sources, having a resolution of a three-dimensional image, will provide important information for better understanding of the geodynamical process in central Japan.

著者

安里 進

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.105, no.3, pp.364-371, 1996-06-25 (Released:2009-11-12)

参考文献数

33

---

Is it possible that modern Ryukyuans are the descendants of Palaeolithic Minatogawa Man, and the people of the Shellmound Period, which is partially equivalentto the Jomon Period ? There is a blank period of about 10, 000 years between the Minatogawa population and the population of the Okinawan Shellmound Period. Sakishima prehistoric culture was one of the Southeast Asian prehistoric cultures until the beginning of the Heian Period. A dramatic cultural change occurred in Okinawa after the Shellmound Period, in the Gusuku Period, which began in the 10th to 11th centuries as a result of culturalinfluence from the Mediaeval Period of Kyushu. Darling 13th to 14th centuries the culture of the Gusuku Period also expanded into the Ryukyu Islands from Amami Islands to the Sakishima Islands, and there was a general rapid population increase. Modern Ryukyuans are descended from the populations of the Gusuku Period. Some geneticists and anthropologists insists that modern Ryukyuans possess hereditary blood factors found in northern Asian populations. It is suggested that those factors flowed into the Ryukyuan population in the Gusuku Period.

著者

小林 貞一

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.89, no.6, pp.361-371, 1980-12-25 (Released:2009-11-12)

参考文献数

59

著者

岡 秀一

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.100, no.5, pp.673-696, 1991-10-25 (Released:2010-10-13)

参考文献数

58

被引用文献数

5 4

---

A forest limit marks a distinct change in landscape, but it includes a variety of elements. In this study, the forest limit altitudes all over Japan were compiled, the relationship between the specific features of their distribution and thermal conditions were discussed.The forest limit altitudes on 211 mountains ranged from below 1, 000 meters in Hokkaido to 2, 800 meters in Central Honshu, and difference in these altitudes extended about 2, 000 meters between 35° and 45° North Latitude. Horizontally, these altitudes are distributed concentrically, focusing on the Taisetsu Mountains and the Hidaka Mountains in Hokkaido and the Akaishi Mountains in Central Honshu. The zone ranging from the southern part of Northern Honshu to the northern part of Central Honshu is crowded with isopleths, forming a division between the sides of the Japan Sea and Pacific Ocean. Calculation the Warmth Indices (WI) of forest limit altitudes, we find that their frequency distribution ranges from 16.1°C·M to 50.4°CEM, and their modes are 25 to 35, 34 to 40, and 25 to 30°C·M in Hokkaido, Northern Honshu, and Central Honshu, respectively. Reviewing these data individually, we see that forest limits are seldom equivalent to WI 15°C·M, which has been set as a boundary between the alpine and subalpine zones. In reality, it becomes increasingly difficult for the forest limit to converge on a particular WI value due to a variety of causes. It is worth noting, however, that at least there are some mountains on which the forest limit altitude is extremely close to WI 15. In such a situation, the WI 15 is of great importance, because it indicates that forests are capable of growing at least to that extent in terms of thermal conditions. This is the reason why WI 15°C·M is worth notice, and therefore the relationship between its altitude distribution and the forest limit altitude was determined. Additionally, the relationship between mountaintop altitude and forest limit altitude was also investigated. The correlation coefficient of the latter is more closely related than the former. But we must emphasize that the latter is only a seeming relation. Why? It is true that the higher the mountain, the higher the limit altitude, but the fact is that the limit altitude will not rise endlessly in step with the height of a mountain.Then, another relationship was examined, concerning differences not only between WI 15 altitudes and forest limit altitudes but also between mountaintop altitudes and forest limit altitudes, using the variation coefficient to verify the dispersion in these differences. As a result, we found out that dispersions are smaller in the former (WI 15 and forest limit) th an in the latter and that forest limit altitudes are more closely related to thermal conditions. On the other hand, the differences between WI 15 altitudes and the forest limit altitudes are defined by mountaintop altitudes. Additionally, the depth of snow cover strongly affects the difference in forest limit altitudes, if mountaintop altitudes are the same.The role of thermal condition, mountaintop altitude and snow depth condition for determining the forest limit altitude should be easy to determine as Fig. 10. Namely, altitudes of forest limit are primarily decided by thermal conditions depended on their geographical situation. They are secondarily modified by altitude of mountain. When the mountain altitudes are equivalent, snow depth conditions affect the forest limit.

著者

工藤 広忠

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.76, no.2, pp.102-106, 1967-04-25 (Released:2009-11-12)

参考文献数

9

---

The author describes the oil production, history and geology of the oil field in Szechuan which has been in progress recently. The interesting oil episode by Zhu-Ge-Kong-Ming, a famous politician, are also added.

著者

吉川 虎雄

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.72, no.1, pp.8-24, 1963-01-30 (Released:2009-11-12)

参考文献数

10

---

In February, 1957, the Japanese Antarctic Research Expedition established a station, called “Syowa”, on a small island off Prince Olav Coast, East Antarctica. The station had been occupied by the wintering teams untill February, 1962, except during the period from February, 1958, to January, 1959. Various kinds of scientific observations, for example, aeronomy, meteorology, geology, geomorphology, glaciology, biology, and so on, had been carried out at the station and on its surrounding Antarctic continent. The station was temporarily closed in February, 1962, on account of logistic and financial difficulties, and the reopenning of the station for scientific activities is now being discussed by the Japanese government.In this paper, activities of the Japanese Antarctic Research.Expedition are described and some of scientific results in geography, geology, geodesy, glaciology, and so on are briefly explained.

著者

日本地学史編纂委員会

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.101, no.2, pp.133-150, 1992-04-25 (Released:2010-12-22)

参考文献数

31

被引用文献数

3 1

著者

増田 富士雄

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.100, no.6, pp.976-987, 1991-12-05 (Released:2009-11-12)

参考文献数

54

被引用文献数

1 2

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The history of global climate on the earth during these 600 million years is presented based on the oxygen isotope data of fossil shells. The paleoclimatic curves clearly show the cyclic changes with different frequencies, such as, glacial-interglacial cycle of 0.1 Ma and Fischer-Arthur cycle of 32 Ma, and Greenhouse-icehouse cycle of 300 Ma. Today is located in the interglacial period of icehouse state. There are essential differences of the environmental systems and conditions between the greenhouse and icehouse states. The greenhouse state characterized by no continental ice sheets, simple climatic zones, more carbon dioxide in atmosphere, small annual temperature range, warmish and humid poles, high sea level, wide continental shelves, low latitudinal and vertical gradients of seawater temperature, warm oceans, slow circulation of bottom currents, anoxic oceans, abundant marine organisms, black shale deposition of oil raw material, sulfide deposits on oceanic ridges, manganese deposits on continental shelves, active magmatism, first spreading, magnetic quiet and active orogeny. A modern greenhouse warming was also compared with the warming after the “Younger Dryas Event” in the postglacial age.

著者

杉原 重夫 嶋田 繁

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.107, no.5, pp.695-712, 1998-10-25 (Released:2009-11-12)

参考文献数

45

被引用文献数

2 3

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Hachijo Island, located on the volcanic front of the Izu-Ogasawara (Bonin) arc, consists of two stratovolcanoes : Nishiyama and Higashiyama. Nishiyama (Alt. 854.3 m) is a scarcely dissected cone called “Hachijo-fuji”. Nishiyama began its volcanic activities about 10, 000 years ago. Many lateral volcanoes exist around Nishiyama, and one of them, Kandoyama (Alt. 194.9 m) is a tuff cone which was formed by a phreatomagmatic eruption. This study discusses the stratigraphy of deposits, and the eruptive types and the eruption ages of Nishiyama after the formation of Kandoyama. The results are summarized as follows.1) This study names four air-fall pyroclastic materials “Ny1-4”, which erupted from Nishiyama after the pyroclastic surge eruption of Kandoyama (ca. 2, 500 y.BP). All of them are scoriaceous.2) Ny2 erupted from a lateral volcano on the west of Kandoyama. This scoria cone is composed of agglutinate.3) Ny3 erupted from the summit crater of Nishiyama ca. 1, 100 y.BP. Ny3 was widely distributed on the southeast flank of Nishiyama, but it did not reach the foot of Higashiyama. Prior to the eruption of Ny3, a large amount of lava flowed down the southeast flank of Nishiyama.4) Ny4 erupted from a crater row along the southeast side of Nishiyama. From the description found in archives, it is clear that the eruption of Ny4 corresponds to A.D. 1605 (Keicho 10th) eruption. Ny4 deposited around the vents as agglutinate, and air-fall materials were widely distributed on the southeast side of Nishiyama. However, the total volume of Ny4 was the same or less than that of the Miyakejima 1983 eruption and the Izu-Oshima 1986 eruption.5) There are descriptions in the archives of at least four eruptions and about ten occurrences of earthquakes and tsunami in and around Hachijo Island. The fissures and tsunami deposits which followed historic earthquakes were found at the Yaene site located on the south side of Nishiyama. The pyroclastic materials from Nishiyama date these past earthquakes.