著者
中村 一明
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.75, no.2, pp.93-104, 1966-04-25 (Released:2009-11-12)
参考文献数
14

Taal Volcano, situated at SW part of Luzon Island, Philippines, erupted during 28th to 30th, September 1965 after fifty-four years of quiescence.As an example of a magmatophreatic eruption of basaltic volcano, this paper deals with the course and the ejecta of the eruption with special reference to the horizontal blasts, based both on a paper by MOORE et al. and on the writers field observation. Topography of the island and historical records of eruption are examined from the same viewpoint by literature survey.Taal Volcano is an island in Taal Lake and is 25 km2 in area with a summit crater 2 km in diameter. The volcano island is composed almost of pyroclastic materials which are the product of past magmatophreatic eruptions. Sixteen craters are found on the slope of the main flat cone and they are wide in proportion to their height suggesting their origin to be explosive eruptions.No historical record describes quiet effusion of lava flows, but it indicates explosive nature of eruption.Essential materials responsible for the present eruption was titanaugie-olivine-basalt. The eruption continued for about 60 hours and no lava flow issued. The area of about 60 km2 was covered by new pyroclastic ejecta more than 25 cm thick. New elongate explosion crater was opened by the present fissure explosion on the southwestern slope of the main cone.From the base of explosively rising eruption clouds, horizontal blasts spread out in all directions. The blast is turbulent mixture of mud, lapilli, blocks and crept on the surface of the ground with hurricane velocity and near the crater it spilled over a ridge of 300 m in relative height (summit crater rim). But it tended to spread on lower places as it proceeded further away from the crater. Parts of the blast crossed the lake surface over 2 km and caused much damage to the villages at opposite lakeside. The blasts left giant ripples on the surface of the deposits within 2 km from the crater. The wave-length of the ripples decreases regularly from 15 m to 3 m as the distance from the crater increases.The blasts are regarded to be a low temperature pyroclastic flows. The mobility of the flow is thought to be maintained only by the initial formation of a fluidized system. Because, no delayed vesiculation is expected since the essential material is basaltic in composition, and also because the internal turbulence caused by envelopment of cold air is not great enough, since the temperature of the flow was only about 100°C or below. Magmatophreatic explosion through layers of pyroclastics seems to have been a favourable condition for the initial formation of the fluidized system.
著者
小山 真人
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.222-232, 2002-04-25 (Released:2009-11-12)
参考文献数
73
被引用文献数
7 8

Previous studies have reported many examples of possible mechanical coupling between volcanic unrests and large earthquakes, which occurred around the volcano. This paper reviews these studies and reorganizes the types of mechanical coupling into the following five cases (cases A-1, A-2, B-1, B-2, and C) and 10 mechanisms : In case A-1, in which a large earthquake triggers activation of a volcano, the following four mechanisms can explain their coupling : (A-1-1) an increase in compressional stress, which was produced by earthquake source faulting, squeezes magma up to the surface; (A-1-2) an increase in differential stress (or magma pressure), which was produced by earthquake source faulting, promotes dike intrusion; (A-1-3) increase in tensional stress, which was produced by earthquake source faulting, triggers gas bubbling in magma; and, (A-1-4) dynamic stress change, which was associated with seismic wave, triggers gas bubbling in magma.In case A-2, in which a large earthquake triggers deactivation of a volcano, the following three mechanisms can explain their coupling : (A-2-1) increase in compressional stress, which was produced by earthquake source faulting, chokes a vent or prevents gass bubbling in magma; (A-2-2) decrease in differential stress (or magma pressure), which was produced by earthquake source faulting, prevents dike intrusion; and, (A-2-3) increase in tensional stress, which was produced by earthquake source faulting, drains magma back toward a chamber.In case B-1, in which a volcanic unrest triggers a large earthquake, coupling can be explained by mechanism B-1-1 : change in stress, which was produced by dike intrusion (or pressure change in a magma chamber), promotes earthquake source faulting. In case B-2, in which a volcanic unrest prevents a large earthquake, coupling can be explained by mechanism B-2-1 : change in stress, which was produced by dike intrusion (or pressure change in a magma chamber), prevents earthquake source faulting.In case C, in which a change in plate motion causes a stress change and then triggers (or prevents) a large earthquake (or a volcanic unrest), coupling can be explained by mechanism C : stress change promotes (or prevents) earthquake source faulting or ascending / intrusion of magma.
著者
堀 和明 斎藤 文紀
出版者
Tokyo Geographical Society
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
9 13

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.

33 0 0 0 OA 擦文文化

著者
藤本 強
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.90, no.2, pp.122-136, 1981-04-25 (Released:2010-11-18)
参考文献数
30
被引用文献数
1 1

The Satsumon culture was in existence in Hokkaido from 9th to 13th century A.D. as a Pre-Ainu culture of Hokkaido. The Satsumon culture succeeded the Post-Jomon culture. The Satsumon culture was formed on the basic cultural elements of the Post-Jomon culture. Some cultural elements from Japanese culture of that time were added to them. The basic cultural elements of the Post-Jomon culture had their roots in late or the latest Jomon culture in northern Japan. So, the Satsumon culture can be regarded as one of the direct descendants of the late or the latest Jomon culture in the northern Japan.About two thousands years ago, rice cultivation began in Japan. At first, rice cultivation was practised in southwestern Japan and it gradually expanded to the east. Finally, it reached the southern Tohoku district, but it could not penetrate into northern Tohoku and Hokkaido. In the northern Tohoku and Hokkaido, people lived on fishing, gathering and hunting as was the case in the previous Jomon period. After the introduction of rice cultivation, the livelihood of people in Japan was separated into two different ways. In most parts of Japan, in southern Japan, people depended on rice cultivation and in the northern extremity of Japan, people lived on fishing, gathering and hunting.
著者
相馬 清二
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.84, no.4, pp.204-217, 1975-08-25 (Released:2009-11-12)
参考文献数
8
被引用文献数
3 3

A violent fire-tornado has broken out at the former site of the Army Clothing Depot in combustion caused by the destructions of the Great Kanto Earthquake at 3.30 p.m. September 1, 1923. By this fire-tornado, about 40 thousand people have been burned to death in a moment. An interpretation that the fire-tornado has been caused by passage of a cold front has generally dominated academic circles in this field up to date. According to the detailed reexaminations, this interpretation included many inconsistencies. We could obtain recently the various data with respect to the fire-tornado which occurred in the last several years. From these data, it became clear that the fire-tornadoes often have occurred near a combustion area.An example which was the most similar with the fire-tornado at the former site of the Army Clothing Depot was found out in the combustion of Wakayama City by an air raid on July 9, 1945. 748 persons have been burned to death by the fire-tornado in this city.Finally, our study leads to the conclusion that the fire-tornado at the former site of the Army Clothing Depot was caused by the widespread great fire following the Great Kanto Earthquake. There was a cold front in northwestern direction of Tokyo, but it did not play the leading role for formation of the fire-tornado.
著者
遠藤 毅
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.113, no.6, pp.785-801, 2004-12-25 (Released:2009-11-12)
参考文献数
13
被引用文献数
20 13

The Tone River which has the largest river basin in Japan rises in Mt. Oominakamiyama in the northern part of Gunma Prefecture. It runs down south to Maebashi City, and changes course to the east, then discharges into the Kashimanada Sea at Choshi City in Chiba Prefecture. It, however, used to flow south near Kurihashi Town in Saitama Prefecture, which lies mid-way between Maebashi and Chosi, and flowed in to Tokyo Bay. This rerouting was achieved by the work of the Tokugawa Bakufu in 1654. Before rerouting, the estuary had been in the northern part of the present Sumida Ward, the eastern part of Tokyo. In the estuary area, which corresponds to the Kohtoh region, consisting of Sumida and Koto Wards and the eastern part of Edogawa Ward at present, the sea was shallow and a lot of sand bars scattered over. The Kohtoh region naturally had favorable conditions for reclamation.When Ieyasu Tokugawa entered Edo Castle in 1590, the environs of the castle were limited, because the east side of the castle faced to an inlet called Hibiya Irie, and the other sides were surrounded by rough plateaus. Topographically the site was good for a fortress but too small to make a town and farming estate. Soon after his settlement, Hibiya Irie was reclaimed to build a town for warriors and citizens, and the Onagi cannel was excavated in the shallow sea which spread on the east of the Edo City for transporting food and salt. The soil dredged from the Onagi channel was used for filling the northern part of the channel. It was the first reclamation work in the Koto sea region. Since then reclaiming works have continued in the Koto sea region, which used to be the estuary of the Tone River. A lot of land has been reclaimed due to garbage disposal in the city since 1655.In the Tokyo Bay area, about 2, 700 ha was had reclaimed during the Edo era period over 270 years, and about 6, 000 ha from Meiji Era to the present over about 140 years. As a result of those reclamation works, the sea area of the Koto region has been replaced by man-made lands, with the exception of some ship routes.
著者
山川 修治
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.102, no.2, pp.183-195, 1993-04-25 (Released:2010-11-18)
参考文献数
60
被引用文献数
1 3

Natural disasters in Little Ice Age (c. 1550-1850) and its climatic variations which formed a significant background for the disasters are mentioned. Cool summers due to a prevailing Okhotsk High were characteristic of this period. Cold winters, summer heavy rains and unstable atmospheric conditions also constituted essential features of Little Ice Age. Aerosol ejected by a series of major volcanic eruptions partly prevented solar radiation from reaching the earth' s surface (parasol effect), which resulted in cool and unusual weather. Agriculture, in particular, was vulnerable to bad weather damage. As a result of decreasing direct insolation, sometimes together with lowering temperature and/or locally increasing precipitation, seven major famines occurred during the Edo Era (1663-1868) which approximately coincided with Little Ice Age. Several cases in this paper suggest that natural environment in Little Ice Age was marked by both volcanism and weakened solar activities which “Maunder Minimum”(1645-1715) represented.
著者
河名 俊男 中田 高
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.103, no.4, pp.352-376, 1994-08-25 (Released:2009-11-12)
参考文献数
47
被引用文献数
37 48

In 1771, according to several trustworthy historical records, a huge tsunami named the Meiwa Tsunami washed the southern part of the Ryukyu Islands killing about 12, 000 people. The tsunami attributed probably to a large earthquake generated by a submarine thrust fault along the Ryukyu Trench. The southern Ryukyu Islands consisting of Miyako, Irabu, Shimoji, Tarama, Ishigaki, Iriomote and other small islands are fringed by coral reefs, and large Holocene coralline boulders possibly transported by past tsunamis, are extensively distributed on land and reef flats. Among these boulders, those composed of aragonite by 100% or nearly 100% are reliably dated by the radiocarbon method, and are good evidence for inundation, run-up heights and timing of tsunamis in the past.In order to infer the timing of past tsunamis, we dated samples carefully collected from the uppermost parts of these Holocene coralline boulders and fragments. Based on 65 dates, we restored a tsunami history in the area during the past several thousand years.Most of the coralline boulders we dated are much older than the age of the Meiwa Tsunami about 200 yr BP. Certain periodical distributions of the ages among the boulders suggest that the area had been attacked by huge tsunamis around 600, 1, 100, 2, 000 and 2, 400 yr BP during the last 3, 000 years. Thus tsunamis which brought tsunami boulders on land occurred repeatedly with intervals of several hundred to one thousand years in the study area.The tsunamis occurred around 1, 100, 2, 000 and 2, 400 yr BP were judged from the distribution of boulders of similar ages, that they were generated along the Ryukyu Trench while that of 600 yr BP along the Okinawa Trough.The tsunami about 2, 000 yr BP is most reliably restored among the past tsunamis in the area and is named the “Okinawa-Sakishima Tsunami”. This tsunami attacked an extensive area from Miyako to Ishigaki islands and transported many huge tsunami boulders such as “Tsunami Oishi” deep on land.
著者
増田 隆一
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.354-363, 1996-06-25 (Released:2009-11-12)
参考文献数
30
被引用文献数
1 1

The richness of fauna diversity is seen on the Japanese Islands, which range through 3, 000 km. When and from where have theanimals immigrated to Japan? Also, for understanding natural history of the Japanese Islands, it is very importantto investigate evolutinary history and origin of animals distributed on each island. While the evolutionary questions have been paleontologically and geologically examined so far, some of them are still unclear. Recent development of molecular phylogenetic study provides a reliable sight to understanding evolutionary history and origin of species. Advantageously, molecular study can analyze phylogeny of living species without fossil data.In Japan, two wildcats, the Iriomote cat and the Tsushima cat, live on the Iriomote Island and the Tsushima Island, respectively, where land bridges between the Asian continent and the Japanese Islands were present in the past time. To know evolution of these wildcats gives us useful information for better understanding of natural history of the Japanese Islands. Moreover, because both the wildcats are now endangered, it is now strongly needed to understand phylogenetic status of them for conservation and management. For the reason, we investigated molecular phylongeny of the two wildcats based on mitochondrial DNA sequences, and revealed that both the wildcats are very closely related to the leopard cat Felis bengalensis, which is widespread throughout Asia. Furthermore, from the DNA data, the Iriomote cat and the Tsushima cat were estimated to have diverged from the continental leopard cat approximately 200, 000 and 100, 000 years before present, respectively. The dates estimated by molecular data were in concordance with formation dates of the Ryukyu Arc and the Tsushima Island, respectively. These results suggest that geographic barrier has led fixation of some unique morphological characters into each cat population, while the two Japanese wildcats are still genetically close to the continental leopard cat.
著者
重村 利幸
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.105, no.4, pp.448-458, 1996-08-25 (Released:2009-11-12)
参考文献数
13

Iwo Jima is small volcanic island located isolate in the Western Pacific Ocean about 1, 250 km south of Tokyo. The island with the area about 23 km2 is covered with considerably dense vegetation and no rivers exist in this island. Thus, the source of sediments to nourish the beach seems to be quite limited in this island. Further, the coast is always subjected to rough seas because it is fully exposed to the open sea. Nevertheless, the coast is mostly rimmed by sandy beaches with about 200 m in width and the shoreline is still advancing toward the sea which increases the beach area year by year. Many scientists have pointed out that this increase might be caused by an unusual upheaval of this island exceeding 30 cm per year. However, no quantitative analyses have been done yet on this unique phenomenon that prevents from constructing any port facilities in this island. Thus, the author intends to investigate the features of the long-term variation of the area which have occurred in Iwo Jima during the past seven decades and to examine its variation mechanism.To investigate the features of the long-term variation, analyses are conducted on the seven maps and charts of Iwo Jima which have been published in the period from 1911 to 1981. The analysis reveals that the island has kept increasing its area over the past seven decades although the increasing rate has changed drastically in 1952 from 30, 000 m2 to 90, 000m 2 peryear and that the increased area has reached roughly 4.3 km2 in total during the sevendecades. This change of the increasing rate well corresponds to the fact that the upheaval rate of the island has changed in 1952 from roughly 10 cm to 30 cm per year which has been found by Kosaka et al. in 1979.To examine the effect of the upheaval on the features of the long-term variation of the area, calculation is carried out by giving the various values of imaginary upheaval to the bathymetric data shown on the chart covering the sea around Iwo Jima published by the Hydrographic Department of Japan Maritime Safety Agency in 1981. The result of the calculation indicates that the upheaval of 10 cm per year corresponds to the increasing rate of the beach area roughly 43, 000 m2 per year and the upheaval of 30 cm per year corresponds to the increasing rate of the beach area roughly 130, 000 m2 per year when the foreshore slope is assumed to be 1/20. These values are surely the ones before the beach is transformed by the action of the ocean waves. However, comparison of these values with the ones found through the former analyses indicates that the calculation has provided quite a reasonable estimation of the increase of the beach area. These findings clearly indicate that the continuous upheaval is the governing factor to cause the increase of the beach area in Iwo Jima.
著者
石橋 克彦
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.108, no.4, pp.399-423, 1999-08-25 (Released:2009-11-12)
参考文献数
75
被引用文献数
12 16

A large volume of historical documents in Japan show that great subduction earthquakes have repeatedly occurred along the Suruga-Nankai trough off southwest Japan since A.D. 684 with an interval of 100-200 years. They occurred as pairs of M8 events, one in the eastern half (Tokai earthquake) and another in the western half (Nankai earthquake), as was the case for the 1854 Ansei earthquakes, while sometimes occurring as single giant events like the 1707 Ho'ei earthquake. Although the space-time pattern of their recurrence is the best-known in the world, we should study more past events in order to understand the tectonophysical bases of their recurrence. In this respect I review the present understanding of historic Tokai and Nankai earthquakes and discuss related problems from the viewpoint of historical seismology. In this paper, the first of the three in all, I review the events until the early half of the 14th century. The keys to identifying older events are strong ground motion and damage in Kyoto, Nara, and Osaka, those in wider area of southwest Japan, tsunamis along the Pacific coasts of southwest Japan, typical coseismic vertical crustal movements of the Kochi plain, the Muroto and Oma'ezaki points, and the Ise and Suruga Bay coasts, temporal inactivity of specific hot springs, and aftershock activities recorded in Kyoto. The 684 Hakuho earthquake was definitely a Nankai event, and possibly included a Tokai event simultaneously (possibly Ho'ei type). The 887 Nin'na earthquake was also a definite Nankai event and was probably a Tokai event as well (Ho'ei type). The 1096 Eicho earthquake was clearly a Tokai event, but the following 1099 Kowa earthquake has some discrepancies that prevent it from being regarded as a M8 Nankai event. It is not clear yet whether great earthquakes occurred or not in the ca. 200 year intervals of 684-887 and 887-1096. It seems probable that great Tokai and Nankai earthquakes took place in the mid-13th century, but a more detailed investigation of historical seismology is required to discover the missing event.
著者
矢嶋 澄策
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.72, no.4, pp.178-188, 1963-08-30 (Released:2009-11-12)
参考文献数
10
被引用文献数
1

Survey of old records concerning the publication on mercury provides a very useful means to trace exhausted and forgotten mercury mines and thus complete the gaps in the distribution of mercury are deposits in the Japanese segments of the Circum-Pacific metallogenetic zone.The discovery of a mercury mineral in 198 A. D. is described in “Shoku Nihonki”, the earliest literature referring to the Japanese mercury. The mining of the metal in record, however, dates as far back as the Asuka period (600 A. D.) and a peak production was once reached during the Heian period. In those early days, mercury was used principally for medicine, amalgam base for gold-gilding on Buddha statues, and ship paint. The mining was operated throughout Japan by the “Niu” tribe, an ethnic group which was once headed by “Niuzuhime” in Yoshino region and later spread out searching for new deposits. “Niu” means cinnabar and also red color in Chinese. For this reason, villages in former mercury-producing district often bear the name of Niu and have shrines called “Niu Jinja” which are dedicated to Niuzuhime.It is also reported in literature that the search for mercury was also conducted by “Yamabushi”, a group of itinerant buddhist priest who travelled around the country carrying the will of Kobo-daishi, the famous founder of their sect.Although the occurrence of mercury in “Hitachi” and “Dewa” districts was mentioned in ancient literature, no mercury deposits have been discovered geologically in recent years. The mercury contents of reddish clays from these localities, however, are high enough to be indicative of the presence of such are deposits.
著者
岡田 篤正 松田 時彦
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.101, no.1, pp.19-37, 1992-02-25 (Released:2010-10-13)
参考文献数
42
被引用文献数
11 7

The Neodani fault to the north of Nagoya, central Japan, is a principal strand of the Nobi fault system. The fault moved primarily in a left-lateral sense during the great Nobi earthquake of 1891 (Magnitude 8.0). The maximum vertical and horizontal offsets are 6 m at Midori and 7-8 m at Naka, respectively. After reviewing previous works, we discuss new geomorphological and geological data bearing on the 1891 and earlier paleoearthquakes in the latest Quaternary: specifically we find that1) The 1891 vertical offset was about 5 m at the western slope of Terayama which is located on the northwestern extension of the well-known Midori fault scarp.2) The subsurface data show that the vertical offset of the base of the alluvial deposits beneath the Midori scarp is about same as that of the ground surface at the scarp, implying that the 1891 event was the first faulting event since the beginning of the deposition of the allu-vium. The radiocarbon date suggests that the alluvium is not older than 1, 000 years in age.3) The lower river terrace, ca. 14, 000 years old, is displaced as 14 m vertically at Terayama in Midori where about 5 m vertical displacement occurred in 1891, and a stream incising the lower terrace on the fault line at Naka offsets ca. 28 m laterally where 7-8 m lateral displacement occurred in 1891. If the fault is characterized by the repeated occurrence of earthquakes of the same size, both the 14 m vertical offset at Terayama and 28 m lateral offset at Naka may be interpreted to be the result of 3 to 4 events occurring at average intervals of about 3, 000-4, 000 years since the formation of the lower terrace. The observation also indicates that the Neodani fault, at least in the central segment including Midori and Naka, has averaged 2m per one thousand years in the left-lateral slip rate in that period.
著者
木村 政昭
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.259-285, 1996-06-25 (Released:2009-11-12)
参考文献数
53
被引用文献数
76 83

Compilation of seismic reflection profiles, rock sample analyses and manned and non manned diving observations revealed that land bridges, connecting the Ryukyu Arc to the Chinese continent, have appeared in two stages since the late Pliocene. The first stage occurred before the deposition of Pleistocene Ryukyu Limestone and ceased in the early stages of deposition, while the second was apparent during the middle and late stages of the Ryukyu Limestone. The land bridge in the first stage may have appeared between 2.0-1.0 Ma and is well identified by the unconformity between Shimajiri and Ryukyu Groups before the deposition of Ryukyu Limestone. The land bridges may have appeared two or three times in the second stage during or after deposition of Ryukyu Limestone between 0.4-0.02 Ma. The last land bridge may have appeared during the Würm glacial stage in the late Pleistocene, connecting the Chinese continent through Taiwan, Okinawa and Amami-Oshima to the Kyushu main land. This supports the hypothesis that the Minatogawa Man migrated to Nansei-shoto Islands passing through the land bridge in the Late Pleistocene.

14 0 0 0 OA 人工地震の役割

著者
早川 正巳
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.81, no.1, pp.27-47, 1972-02-25 (Released:2010-02-25)
参考文献数
7

人工地震・地震探査あるいは地震探鉱という言葉はすでに我々には耳なれたものであるが, 案外, その利用や現状については知られていないこともある。編集委員会からの要望に応えて, ここに筆をとつた。利用などかなり広範囲なので不充分な点があると思う。おゆるしいただきたい。上にしるした三つの言葉の意味は, 大体同じようなものであるが, はじめの方ほど広い意味ぐらいにとつてもらえばよかろう。本文でははじめの人工地震を用いることにする。人工地震はどのようにして発展してきたのであろうか, 最初は石油, 石炭などの地下資源をしらべることから始まつたのであるが, 次第にその応用も広まり, 更には地殻の構造解明にまで発展してきた。そのためには陸地のみならず, 海洋においての人工地震の技術が大いにあずかつて力となつたのである。ここではまず, 前半ではこれらの人工地震の歴史をひもとき, またその歴史と関連して, その技術の進歩が如何にその時々の関連学問, 技術の発展や社会情勢の影響をうけたかをふり返つてみる!後半では人工地震でしらべられる構造をその規模の大小に応じて, 小さな方から順次大きな方に実例を用いて説明してゆくことにする。
著者
中村 有吾 松本 亜希子 中川 光弘
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.114, no.4, pp.549-560, 2005-12-25 (Released:2009-11-12)
参考文献数
18
被引用文献数
8 6

The AD1663 ejecta of Usu volcano, western Hokkaido, northern Japan, have a thickness of approximately 200, cm and are divisible into 7 units on the eastern foot of Usu volcano. The basal deposit, Unit-A, is composed of fine-grained, poorly sorted pumice and ash with well-developed stratification. It contains base surge beds near the sources, and is interpreted as phreatomagmatic in origin. Unit-B is typical in many respects of the product of plinian activity. It is characterized by coarse grain size and wide dispersal, combined with low lithic contents and poor development of internal stratification. This fallout deposit (Usu-b tephra) can be seen in the eastern regions of Usu volcano, and has a thickness of about 4 cm at 200 km from the vent. Unit-C, Unit-E, Unit-F, and Unit-G have characteristics that are satisfactorily interpreted as a consequence of phreatomagmatic activity : fine grain size near source, poor sorting, well-developed stratification and base surge bedforms. Unit-D is typical of phreatic deposits, being composed largely of non-juvenile lithic fragments.According to historical records, the eruption was preceeded by earthquake swarms for 3 days from August 13, 1663. The first eruption (Unit-A) occurred on August 16, followed by an eruption associated with a large amount of pumice and ash (Unit-B) on August 17. The explosive eruptions lasted approximately 20 days.The petrographic properties of the plinian product differ considerably from those of the phreatomagmatic products. The pumice clasts of Unit-B contain abundant glass and little phenocryst (plagioclase, orthopyroxene, and hornblende). The glass has a relatively high refractive index (n = 1.490-1.492) and a low SiO2 content. Orthopyroxene in Unit-B has a relatively high refractive index (γ = 1.735-1.740) and low Mg#. The phreatomagmatic products are rich in massive glass. This glass has a relatively low refractive index (n = 1.475-1.490) and a high SiO2 content, with values differing among horizons. The compositional diversity of the 1663 products indicates the existence of some magma. Presumably, their mixing triggered the 1663 eruption of Usu volcano.
著者
西上 欽也 田所 敬一 永井 悟 水野 高志 加納 靖之 平松 良浩
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.268-276, 2002-04-25 (Released:2009-11-12)
参考文献数
21
被引用文献数
1 1

This paper briefly reviews the triggering characteristics of injection-induced seismicity. Water injection experiments were carried out in the Nojima fault, southwest Japan in 1997 and 2000 to detect the healing process of the fault zone after being ruptured by the MJMA 7.3 Hyogo-ken Nanbu (Kobe) earthquake in 1995. During the experiment in 2000, ultramicroearthquakes of M-1.2 to 1.0 were induced at about 2.5-4.5 km from the injection point and about 4-6 days after the beginning of injection. This space-time migration can be explained by a 2-D diffusion process of pore water pressure. Permeability estimated near the surface, at about 540-800 m depth, is extrapolated well to a depth of 2-4 km where induced events occurred. Other experiments at Matsushiro, central Japan and KTB, Germany also showed similar space-time relationships of induced seismicity. From observations in the Nojima experiment, we obtained characteristic states that suggest differences in the generating process between induced and normal (tectonic) earthquakes. Our findings are as follows : (1) high-frequency component is richer in the waveforms of tectonic events, and (2) the clustering of hypocenters is more dominant in induced events. Further analyses of these observations will lead to elucidating the generating process of induced earthquakes by increasing pore water pressure.