著者
鈴木 毅彦
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.122, no.6, pp.1088-1098, 2013-12-25 (Released:2014-01-16)
参考文献数
40
被引用文献数
1 5

This paper reviews historical volcanic disasters that have affected the Tokyo Metropolitan area and its surroundings, central Japan, and discusses the dangers of volcanic disasters occurring in future. The 1707 (Hoei) eruption of Fuji volcano, the 1783 (Tenmei) eruption of Asama volcano, and the so-called Kanto Loam, volcanic soil deposits containing large quantities of Holocene to Pleistocene fall-out tephras, suggest the potential hazards that originate from volcanic activities. Small to moderate eruptions (VEI 1 to 2) of Asama volcano have resulted in minor ash falls in and around Tokyo every one to two decades. It is most likely that Asama volcano will generate minor ash falls in the near future. Volcanic disasters caused by larger but rare eruptions of VEI 4 to 5 are considered, referring to the 1707 (Hoei) eruption of Fuji volcano, and measures and predictions for the next eruption of Fuji volcano. In this paper, volcanic disasters affecting Tokyo in the near future are not only those caused by ash falls but also those caused by lahar along the Tone, Edo, Sakawa, and Sagami rivers related to Asama, Haruna, and Fuji volcanoes, because the landform developments of these areas in Holocene and historical disasters suggest that these drainage basins have the potential for lahar disasters. In addition, more severe eruptions of VEI 6 to 7 are considered for their impacts and frequencies referring to geological records of air-fall tephras and/or pyroclastic flow deposits such as VEI 6 Hakone-Tokyo tephra (ca. 66 ka) and VEI 7 Aira-Tn tephra (ca. 29 ka).
著者
小山 真人
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.108, no.4, pp.346-369, 1999-08-25 (Released:2009-11-12)
参考文献数
88
被引用文献数
4 8

There remain many challenges in using historical documents to reconstruct a reliable history of earthquakes in Japan. Previous catalogs of historical earthquakes in Japan are not conclusive and contain uncertainties about date, hypocenter, magnitude, and tectonic interpretation of each earthquake. There is no database of digital texts of historical documents, which describe each earthquake. Since the density of historical records in Japan is temporally and spatially heterogeneous, seismologists should carefully remove apparent changes of earthquake frequency, which are caused by the heterogeneity of record density. There is, however, no detailed database of the density variation of historical records. The number of researchers, who are interested in historical earthquakes, is small.The situation stated above is caused mainly by the multi-disciplinary character of historical seismology. Japanese seismologists, who usually have little knowledge of history and classical literature, are not qualified to read a historical document and evaluate its reliability.The environment for research on historical seismology is, however, getting better. Japanese historians have published and are still publishing many historical documents, sometimes with translations into modern language. Evaluations of the reliability of each document can easily be done by referring to historical dictionaries or other databases. All these publications and information are available in many libraries. It is now easy and stimulating for many seismologists to read, evaluate, and interpret historical documents.
著者
大和 広明 三上 岳彦 高橋 日出男
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.120, no.2, pp.325-340, 2011-04-25 (Released:2011-06-30)
参考文献数
12
被引用文献数
17 15

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. 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. 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
山岡 耕春 中禮 正明 安藤 雅孝
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.111, no.2, pp.185-191, 2002-04-25 (Released:2009-11-12)
参考文献数
9
被引用文献数
2 2

The temporal relationship between the interplate and inland earthquakes of Kyushu Island region was investigated. We analyzed this relationship by stacking the temporal frequency of the inland earthquakes with reference to the occurrence time of each major interplate earthquake in the Hyuga-nada region, that occurred between 1900 and 2000. A good coincidence of occurrence between the inland and the interplate earthquakes is recognized. While the tendency of the occurrence after the interplate events has already been pointed out, we found that the inland earthquakes also tend to occur before the interplate events. Abrupt activation of the inland earthquakes within several months before major interplate earthquakes is recognized in addition to the tendency to occurr afterwards. The preceding inland earthquakes may indicate that they are triggered by precursory slow slips around the hypocenters of the Hyuga-nada earthquakes.
著者
田中 和広 石原 朋和
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.118, no.3, pp.499-510, 2009-06-25 (Released:2010-03-26)
参考文献数
34
被引用文献数
6 5

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
米地 文夫
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.97, no.4, pp.317-325, 1988-08-25 (Released:2011-02-17)
参考文献数
37
被引用文献数
2 2 7
著者
村岡 洋文 浅沼 宏 伊藤 久男
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.122, no.2, pp.343-362, 2013-04-25 (Released:2013-05-31)
参考文献数
47
被引用文献数
6 5

Current geothermal power generation from engineered geothermal system (EGS) technologies has two bottle-necks in practical use: one is that the recoverability of injected water is about 50% or less than that in fracture-dominant regions such as Japan, which inevitably requires replenishing large volumes of injected water throughout the power generation operation, and the other is that the injected water raises pore fluid pressures in crustal rocks, causing induced-earthquakes. This paper proposes a new power generation method, which has the potential to resolve these two bottle-necks using EGS technologies in ductile zones. With this method, an artificial brittle fracture reservoir system is completely surrounded by ductile zones at a temperature exceeding 500°C, the presence of which has already been confirmed at the Kakkonda geothermal field, northeastern Japan. The profitability of this method is highly dependent on the depth of drilling, but this concept could dramatically expand exploitable thermal conduction geothermal resources beyond the brittle zones.

53 0 0 0 OA 北海道の豪雨

著者
松本 淳
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.181-193, 1985-06-25 (Released:2010-12-22)
参考文献数
24
被引用文献数
2 2

The climatological characteristics of heavy rainfalls in Hokkaido Island are investigated on the basis of areal frequency distribution of heavy rainfalls (the amount of daily precipitation above 100mm) and geographical distribution of the maximum daily precipitation. The causes of heavy rainfalls and the maximum daily precipitation are investigated on the daily synoptic weather charts, and their geographical distributions are also investigated. Relation between the regional characteristics of heavy rainfalls and the location of the Polar front is discussed. The statistical period is 25 years, from 1973 to 1977 and the data of 256 stations are analysed.As a result, Hokkaido Island is divided into two climatic regions, the one is ‘high frequency heavy rainfall region (HR)’ and the other is ‘low frequency heavy rainfall region (LR)’. The bordering line of these two regions runs approximately from ENE to WSW, from Shiretoko peninsula, via Shiranuka Hills, Ishikari Mountains, Hidaka Mountains, Iburi Mountains to the southern part of Oshima Peninsula.To the south of this line is the HR in which local extremly high frequency heavy rainfall regions are located on the eastern to southern slopes of the mountain ranges. In this region the frequency of heavy rainfalls is more than once per year, and the maximum daily precipatation exceeds 300mm. The main causes of heavy rainfalls here are extratropical cyclones passing to the south of Hokkaido Island from Japan Sea or from Pacific Ocean, most often in August and September. This types of heavy rainfalls are mainly caused by the moist air flow from these cyclones and the effect of orographic rifting strengthens the rainfalls. In these cases the Polar front is usually located to the south of Hokkaido Island.On the other hand to the north of the line, the frequency of heavy rainfalls decreases drastically to less than once per five years. Here the main causes of heavy rianfalls are fronts and tropical cyclones, mainly in July and August. This time the Polar front lies in the northern part of Hokkaido Island and this location corresponds to its mean northernmost position. The region in which the main cause of heavy rainfalls is such northernmost Polar front is classified into ‘frontal heavy rainfall region’. In addition, extremly low frequency heavy rainfall rigion in which no heavy rainfalls were recorded through whole investigated period are discerned.
著者
吉野 正敏
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.118, no.6, pp.1221-1236, 2009-12-25 (Released:2010-03-23)
参考文献数
60
被引用文献数
3 2

The global climate is known to have been relatively warm during the period from the 4th to 10th centuries, although there were slightly different fluctuation patterns locally and regionally. The present article addresses these differences, analyzing the results of previous studies. The warm period is known in Europe as the Medieval Warm Period. Evidence in Japan is also found from the 4th century to the 11th century. Because historical age divisions differ between Europe and Japan, the peak of the Warm Period from the 7th to the 10th century is classified as part of the ancient period in Japan. Therefore, the Warm Period in Japan has been proposed to be called the Nara-Heian Warm Period, Heian Warm Period or Little Climatic Optimum. Based on the water level changes of Lake Shinji in Shimane Prefecture, the present article discusses the warmer climatic conditions in the Heian Period. It also examines old agricultural settlements in the Tohoku District, northern Honshu. People came from Hokkaido or northern Honshu and cultivated rice in the northeastern-most part of Honshu in the 1st century B.C. It is thought that the effect of the warm current branch flowing along the Japan Sea Coast and emerging on the Pacific side through the Tsugaru Straight had an influence on the distribution of rice cultivation at this early stage. Finally, the article shows that the northward shift of the power front of the Central Government (Yamato Chotei) during the 7th to the 9th centuries occurred about 70-80 years earlier in Dewa, an ancient state on the Japan Sea side of Tohoku District, than in Mutsu, also an ancient state on the Pacific side. It is interesting to note, however, that the speed of the northward shift was almost the same on both sides, even though there were different political powers, situations and problems on either side. It is suggested that the northward shift was affected by the warming on the broader space scale.
著者
小山 真人 早川 由紀夫
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.105, no.2, pp.133-162, 1996-04-25 (Released:2009-11-12)
参考文献数
50
被引用文献数
17 14

We reveal the detailed syn-and post-caldera eruptive history of Izu Oshima Volcano, Japan, by tephra and loess stratigraphy. Twenty-four tephra layers, which overlie the slope outside the caldera, show that 24 eruptions occurred since the formation of the caldera (about 1, 450 years ago). These eruptions are separated by 10-200 years clear dormant periods, which can be identified by eolian dust (loess) interbedded with tephra layers. The 24 eruptions can be classified into three types : 1) eruption with scoria and ash falls (12 eruptions), 2) eruption only with scoria falls (7 eruptions), and 3) eruption only with ash falls (5 eruptions). While tephra discharge mass of the type 1 is generally large (1.5×1010 to 7×1011 kg), that of the type 2 or 3 is small (0.6 ×109 to 1 ×1011 kg). The 1986 eruption is classified into the type 2. Debris avalanches, which occurred just before the caldera formation and covered almost all of the Izu Oshima island, demonstrate that the present caldera wall was formed by slope failure of an old edifice. The tephra-discharge stepdiagram, which shows a relationship between time and cumulative discharge volume / mass of magma, shows : 1) the average tephra-discharge rate is constant (92 kg/ s before the N1.0 eruption and 25 kg/s after the N1.0 eruption), showing an abrupt decrease of the rate at about the time of the N1.0 eruption, which occurred about 900 years ago and was the most voluminous eruption for the past 1, 450 years, 2) both before and after the N1.0 eruption, the type 1 eruption shows volume-predictability, that is, the discharge volume / mass of a next type 1 eruption can be predicted, 3) a type 1 eruption should occur sometime in the future again, and when it occurs, the discharge mass of tephra should attain to as much as 2×1011 kg or more.
著者
菱山 剛秀
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.303-314, 2020-04-25 (Released:2020-05-12)
参考文献数
20
被引用文献数
2

The map projections used in Japan at the time of Inoh's map are studied, and the graticule and map projection of his map are examined on the basis of research to date. As many researchers have already pointed out, a contradiction exists between the map projection of Inoh's map and the graticule drawn on it. Ohtani (1917) concludes that the graticule on Inoh's map was drawn using the Sanson–Flamsteed projection and Hoyanagi (1974) concurs that this was certainly the projection of Inoh's map. On the other hand, Unno (1985b) disagrees that the Sanson–Flamsteed projection was used, and instead identifies a trapezoidal projection. Ohtani (1917) also introduces the map-making technology of Inoh Tadataka in detail. Using his technology, survey results are expanded on a plane without modification, and no conversion from a spherical surface to a plane is performed. As a result of verifying the graticule on Inoh's map and his map projection, it is highly probably that the graticule on Inoh's map was drawn with a trapezoidal projection, and it is proved that Inoh's map corresponds well to an equidistant secant cylindrical projection. However, the standard parallels of these equidistant secant cylindrical projection maps vary on every map.
著者
長谷川 昭 中島 淳一 内田 直希 海野 徳仁
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.122, no.3, pp.398-417, 2013-06-25 (Released:2013-07-08)
参考文献数
60
被引用文献数
1 1

Recent investigations based on seismic tomography, hypocenter determinations and focal mechanism analyses using dense seismic network data reveal the precise configurations of the Pacific (PAC) and Philippine Sea (PHS) plates subducting beneath the Tokyo metropolitan area. Estimated geometry shows a broad contact zone between the two plates located directly beneath the Kanto plain. The overlap with the PHS plate subducting above it provides the PAC plate with protection from being heated by the hot mantle wedge. Moreover, the fore-arc portion of the PHS plate, before its subduction beneath Kanto, had been cooled by the subduction of the PAC plate from the Izu-Bonin trench. These cause lower-temperature conditions within the two oceanic plates and the upper continental plate beneath the Tokyo metropolitan area. As a result, depth limits of seismic activities within the plates and along their boundaries are anomalously deep. Seismic tomography studies show that the easternmost portion of the PHS slab mantle is serpentinized. The PHS slab may have been torn in two along the western boundary of this serpentinized mantle, with the eastern portion being left behind relative to subduction of the western portion. This is accompanied by the generation of large intraslab earthquakes along the boundary. We need to take these observations into consideration to understand the mechanism generating M7-class earthquakes, which are anticipated to occur in the southern Kanto region with a high probability.
著者
堀 和明 斎藤 文紀
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.112, no.3, pp.337-359, 2003-06-25 (Released:2009-11-12)
参考文献数
141
被引用文献数
6 8

Large rivers with high sediment discharge, such as the Amazon, Ganges-Brahmaputra, and Huanghe (Yellow) rivers, have formed mega-deltas at their mouths. This paper reviews morphology and sediments of mega-deltas and their Holocene evolution in relation to sea-level changes, channel avulsion, and past-sediment discharge. Application of various radiometric dating techniques to delta deposits, especially since the 1980's has made it possible to clarify delta evolution dynamically on 10-to 1000-year time scales. Most of the deltas are located in developing countries, and have environmental problems principally caused by human activities. For the evaluation of current status and human activities in deltas and drainage basins, both natural and anthropogenic changes of deltas should be analyzed from the viewpoints of geology, sedimentology, and their evolution.
著者
沢田 輝 磯﨑 行雄 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.127, no.5, pp.705-721, 2018-10-25 (Released:2018-11-14)
参考文献数
116
被引用文献数
1 2

The extensive occurrence of a felsic continental crust is one of the unique features of the Earth. The growth history of the continental crust has been a key issue in understanding the origin and evolution of the Earth. In particular, recent geological studies indicate that subduction of the continental crust into the mantle has been greater than previously imagined. The current understanding of the growth of continents and the differentiation of the crust and the mantle of the Earth is reviewed based on a detrital zircon geochronology. One of the most important achievements arises from the analysis of the age structure of individual continents and secular changes over time. The new detrital zircon geochronology suggests that the sizes of the continents have changed over time, which has been an important factor in the growth of the continents. Large continents, such as the modern examples, can preserve older crusts in their interiors, which are separated from active continental margins. Conversely, in the early Earth, continents were probably formed by the amalgamation of small fragments of crust, such as oceanic island arcs. It is speculated that the smallness of the continents was the most significant cause of the poor preservation of Hadean and Archean crusts, despite putative expected active crustal production. Consequently, the recycling of the continental crust occurred in great magnitudes during the early Earth's history. The large-scale subduction of felsic crust represents one of the most important aspects in studies of the early Earth.
著者
吉田 幸平 高木 秀雄
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.129, no.3, pp.337-354, 2020-06-25 (Released:2020-07-11)
参考文献数
22

Science subjects at Japanese high schools are divided into physics, chemistry, biology, and Earth science. The numbers of credits set are two for basic subjects and four for advanced subjects. With a change of courses based on new guidelines enforced by the Ministry of Education, Culture, Sports, Science and Technology Japan (MEXT) in 2012, the Earth science field has classes in Basic Earth Science and Advanced Earth Science. The percentage of high school students who take Earth science classes is estimated from the number of textbooks adopted by MEXT (26% for Basic Earth Science and 1.2-0.9% for Advanced Earth Science), but the percentages of high schools that offer Earth science classes in each prefecture have not been reported. Therefore, the proportion of high schools that offer Basic Earth Science and Advanced Earth Science classes are estimated based on a survey of more than 5,000 high schools in Japan. Data for the survey were collected from the curriculum listed on each high-school homepage and from a questionnaire distributed using the Google mail system. Survey results indicate that 43.7% of high schools nationwide offer Basic Earth Science, and only 8.8% of high schools offer Advanced Earth Science. In addition, the proportion of high schools offering Earth science classes varies depending on the prefecture. The highest proportion of high schools offering Basic Earth Science is 71% (Okinawa) and the lowest is only 4% (Miyazaki). The top prefectural percentage for Advanced Earth Science is 48%, but nine prefectures have no high schools offering Advanced Earth Science. The proportion of high schools offering Earth science correlates with the number of Earth science teachers employed over the past 40 years in each prefecture. However, some prefectures have records only for the total number of science teachers; therefore, the numbers of teachers hired specifically to teach Earth science are not known in these cases. The percentages of high schools offering Earth science classes are higher in prefectures for which only the total number of science teachers is known. A draft is provided on promoting Earth science education at high schools comparing differences among prefectures in the percentages of high schools offering Earth science classes. Based on our results, to promote high school geoscience education, support should be provided through workshops on Earth science education, so that science teachers other than full-time Earth science teachers can recognize the importance of Earth science and teach Basic Earth Science.