著者

LOWE David J. PITTARI Adrian

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.1, pp.117-141, 2021-02-25 (Released:2021-03-18)

参考文献数

122

被引用文献数

2 7

---

西暦232 ± 10年の晩夏にニュージーランド北島タウポ火山で起こった噴火は,過去5,000年間において地球上で起こった噴火のなかでもっとも強力なものであった。噴火は数日から数週間継続し,5つの明確な降下火砕堆積物(ユニットY1~Y5)に続いて,非常に爆発的な噴火による低アスペクト比イグニンブライト(ユニットY6)が堆積した。降下火砕堆積物の内,ユニットY1,Y3およびY4は水蒸気プリニー式噴火によって形成され,Y2とY5はプリニー式噴火であった。Y5とY6は一連の噴火で形成され,非常に強いY5噴火による噴煙柱は高度35-40 kmに達し,それが崩壊することによって非常に高速(600-900 km/h)で高温(最高500°C)の火砕密度流が発生し,ユニットY6が堆積した。このイベントによる堆積物は噴火後十数分で北島中央部の約20,000 km2に及ぶ範囲を覆い尽したと考えられる。また一連の噴火によるマグマ噴出量は約35 km3と見積もられている。この噴火による周辺環境への影響は甚大であり,現代においても農業などの土地利用において火山ガラスを多く含み,コバルトなどの微量元素に枯渇した土壌への対策が必要となっている。

著者

武山 尚生 高橋 佑歌 永田 祥平 澤木 佑介 佐藤 友彦 丸山 茂徳 金井 昭夫

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.129, no.6, pp.899-912, 2020-12-25 (Released:2021-01-18)

参考文献数

56

被引用文献数

2

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The origin of eukaryotic organisms is one of the most important questions in biology. So far, it has been suggested that eukaryotes are phylogenetically related to Archaea. Indeed, recent progress in archaeal genomic biology seems to have accurately determined the exact position of Archaea in the birth of the Eukaryota. In particular, identifying groups of archaeal species, such as the superphylum TACK and the Asgard archaea, has shown that primitive genes for eukaryotic signature proteins (ESP) already existed in the genomes of these archaeal species. Some ESPs are especially important, including actin and tubulin in the cytoskeleton and the ESCRT complex, which is involved in nuclear membrane formation. There have been many reports that eukaryotic intracellular organelles, such as mitochondria and chloroplasts, evolved from specific symbiotic bacteria. Moreover, eukaryotic genes are disrupted by intronic sequences, which must be removed or “spliced” and the exons connected after the primary transcript is generated, to make a mature functional mRNA. Recently, it has been suggested that the self-splicing factor in both bacterial and archaeal genomes, called “group II intron”, may cause gene disruption. In this review, the frontiers of genome biology are summarized in terms of the importance of prokaryotes (both Archaea and Bacteria) for the origin of Eukarya. From an Earth history perspective, how the increase in atmospheric oxygen concentration at 2.4-2.0 billion years ago may have contributed to the rise of the eukaryotes is discussed.

著者

田中 圭 中田 高 松浦 律子 田力 正好 松田 時彦

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.127, no.3, pp.305-323, 2018-06-25 (Released:2018-08-02)

参考文献数

49

被引用文献数

1 1

---

Kambara Jishinyama (earthquake-mound) located on the west bank of lower reach of the Fujikawa river, is widely believed to be a mound that was tectonically formed at the time of the 1854 Ansei Tokai earthquake. Using old maps and aerial photogtaphs, geomorphological changes around Kambara Jishinyama before and after the earthquake are examined. The Fujikawa river frequently flooded and the course on its west bank changed especially after construction of the Karigane-zutsumi (big bank) in order to protect farmland on its east bank. The area around the lower reach of the river was surveyed in 1803 for the Dai Nihon Enkai Yochizu large-scale map, which is the so-called Ino-Daizu. On that map, the river was at almost the same location as its present course. The historical road map (Kaido-Ezu) of Tokaido, which was the trunk road connecting Edo and Kyoto, illustrated in the same period as Ino-Daizu, shows that the Fujikawa river shifted its course close to the foot of river terraces at the west bank. Due to lateral erosion of the river, part of the Tokaido between the towns of Iwabuchi and Kambara collapsed several times. Subsequently, the road was diverted to the new route via Shinzaka as shown on the 1:20,000 scale topographic map published in 1890. A micro-landform classification map of the alluvial lowland of the west bank of the Fujikawa river based on interpretations of aerial photographs taken in 1952 and 1953 reveals that Kambara Jishinyama was located on one of the former mid-channel bars in the braided channels of the river before the 1854 Ansei Tokai earthquake. The earthquake caused a large landslide that dammed the Fujikawa river for a short period at the foot of Shiratori-yama to the north of Iwabuchi. The discharged flood water changed the river course close to the present stream. Geomorphic evidence for tectonic uplift does not exist around Kambara Jishinyama. The Koike river, a small stream flowing in the former main stream of the Fujikawa river, abandoned at the time of the Ansei Tokai earthquake, concordantly flows into the present main stream of the Fujikawa river showing that co-seismic uplift did not take place at the west bank. We conclude that Kambara Jishinyama was not tectonically formed by the earthquake, but is a product of the river course change.

著者

横瀬 久芳 佐藤 創 藤本 悠太 Maria Hannah T. MIRABUENO 小林 哲夫 秋元 和實 吉村 浩 森井 康宏 山脇 信博 石井 輝秋 本座 栄一

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.1, pp.46-68, 2010-02-15 (Released:2010-05-21)

参考文献数

80

被引用文献数

7 20 1

---

To understand the submarine volcanism surrounding the Tokara Islands, a submarine topographic analysis and 67 dredge samplings were carried out. Prior to the submarine investigations, we reviewed comprehensively geological and geophysical data on this region and confirmed the complexity of both volcanic activity and tectonic setting of the Tokara Islands. In contrast to the homogeneous subaerial volcanic rocks comprising predominantly two-pyroxene andesite lava flows, the dredged samples vary from basaltic andesite to rhyolite in composition. Furthermore, we reveal that dacitic and rhyolitic pumices are abundant and broadly distributed throughout the submarine area. The recovered volcanic rocks were mainly subangular to angular cobble-boulder fragments of lava, scoria, and variably vesiculated pumice. Volcanic rocks with hornblende phenocrysts occur only north of the Tokara strike-slip fault, which is a major tectonic element of volcanism. The pumices can be classified into three categories based on the size and abundance of the phenocrysts: aphyric pumice, fine-grained porphyritic pumice, and coarse-grained porphyritic pumice. Occurrences, such as amount in a dredge, shape without extensive abrasion, large fragment size, and bulk rock chemical compositions of the major pumice fragments suggest that they are in situ, rather than originating as drifted pumice or air fall, exotic pyroclastic fragments derived from the four super-eruptions of Kyushu Island. Because dredged samples contained fresh volcanic glass in the groundmass, and are not covered by iron-manganese oxide crust, they appear to have originated from the Quaternary eruptions. Indeed volcanic islands have developed above the submarine erosional terraces (indicated as knick points at approximately 110 m in depth), which is assumed to have formed during the last glacial age. K-Ar age dating on the representative pumice samples resulted in ages of 0.60 ± 0.20 Ma and < 0.2 Ma, respectively. These newly obtained submarine data support that acidic volcanisms occurred around the submarine calderas during the Mid-Pleistocene age.

著者

宮原 ひろ子

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.119, no.3, pp.510-518, 2010-06-25 (Released:2010-08-30)

参考文献数

20

被引用文献数

4 3

---

The relationship between solar activity and climate change in the past can be examined using proxy records. Variations of solar activity can be reconstructed based on carbon-14 in tree rings, which are produced by galactic cosmic rays modulated by the solar wind, while climate change can be reconstructed from changes of tree-ring growth rate or content of stable isotopes in ice cores from the polar region. A comparison of solar activity and climate change at the Maunder Minimum in the 17th century and the Early Medieval Maximum Period in the 9-10th century suggests that the sun plays an important role in climate change even on a decadal time scale. The characteristic variations detected in climate change suggest the mechanism of solar influence on climate involves galactic cosmic rays. Variable features of eleven-year and twenty-two year cycles of solar activity and consequent variations of cosmic rays are possible origins of complex variations of climate change on decadal to multi-decadal time scales. We summarize variations of solar activity and cosmic rays during the past 1200 years and their possible influence on climate change.

著者

Michael J. GROSSMAN 財城 真寿美 三上 岳彦 Cary MOCK

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.4, pp.457-470, 2018-08-25 (Released:2018-10-05)

参考文献数

34

被引用文献数

2

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歴史文書は,気象官署による測器を用いた公式気象観測が開始される以前の台風復元において,貴重な情報源となる。本稿では,1877年の日本(北海道,本州,四国,九州)に影響をおよぼした台風について,詳細な情報を含む5つの資料(1:日本で出版された英字新聞,2:歴史天候データベース,3:日本の灯台気象観測記録,4:イギリスおよびアメリカ合衆国の船舶の航海日誌,5:中央気象台の気象観測表)の検証を行った。そしてこれらすべての資料から,1877年において日本に上陸もしくは接近した4つの台風事例(6月11日,7月26-27日,8月25-27日,10月11日)が明らかとなり,歴史文書は,日本における暴風雨の位置,移動経路,風速,気圧,被害などに関する詳細な情報を含んでいることが裏づけられた。歴史文書に記録された台風に関する情報は,台風の襲来頻度や強度,挙動に関する理解を,気象観測や台風観測の詳細な数値データが十分に得られない過去の時代にまで,さかのぼる可能性を有しているといえる。

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.100, no.4, pp.628-641, 1991-08-25 (Released:2010-11-18)

参考文献数

53

被引用文献数

3 5

---

A brief review of paleomagnetic studies in the Philippine Sea and Izu-Bonin arc including the recent Ocean Drilling Program (ODP) results was made to clarify the present status and problems of the study on the tectonic evolution of the Philippine Sea plate. Paleomagnetic directions observed from the onland and marine areas on the Philippine Sea plate consistently show progressive increase of inclinations with time since the Eocene, and show large (30°-100°) clockwise deflections of declination in Eocene to middle Miocene rocks. These results suggest large clockwise rotation and northward drift of the whole Philippine Sea plate. This paper critically reviews all the models which have been proposed for the tectonic evolution of the Philippine Sea plate and proposes two possible reconstructions which can explain the paleomagnetic results.

著者

岩森 光 中村 仁美

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.1, pp.118-127, 2012-02-25 (Released:2012-03-05)

参考文献数

30

被引用文献数

4 5

---

The generation and migration of geofluids in subduction zones are discussed for the subducting slab and the overlying mantle wedge and crust in terms of theoretical models and observations. Theoretical models include several mechanisms of fluid migration, e.g., Rayleigh-Taylor instability, Stokes ascent, channel flow, and porous flow, whose characteristic lengths and velocities differ significantly. As a result, these mechanisms may occur in different settings within subduction zones. We compare seismic and geochemical observations with the model of fluid migrations, based on which a typical fluid fraction within the mantle wedge is estimated to be 0.1 to 1 vol.%. Accordingly, it is suggested that fluid migration within the mantle wedge is driven by the buoyancy of the fluid, rather than being dragged by the flow of solid matrix. This suggests the fluid rises vertically. In the shallow part of the mantle wedge and within the arc crust, in particular the upper crust, the channel flow seems to be dominant. However, the relationship between these channels and the surface exits observed as volcanoes and hot spring systems is unclear. To better understand fluid distribution and migration, we need to incorporate more observations (e.g., electrical conductivity structure) and models (e.g., models of petrological and thermal structures).

著者

河本 大地

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.5, pp.775-785, 2011-10-25 (Released:2012-01-17)

参考文献数

40

被引用文献数

12 7

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Arguments on geoparks and geotourism have grown heated in recent years. However, few people can understand what “geo” means. This study considers how to share viewpoints of “geo” to build sustainable regional societies from a geographical perspective. First, the author defines geotourism as a type of ecotourism mainly focusing on the Earth's scientific resources. Second, the author argues that the concept of regional diversity proposed by the Japanese Geographical Union in 2005 is the core of Geography. The author has this concept connect the three existing concepts of the geosphere: biodiversity, cultural diversity, and geodiversity. Then, the author discusses promoting geotourism with the concept of regional diversity and familiar geographical views that are important for building sustainable societies. A geographical approach is inevitable for showing the relationship between our lives and “geo”. Humankind will have a better future by locating the geotourism as the main practice of “Earth Science for Society,” which was the slogan of the International Year of Planet Earth 2007-2009 (IYPE), and sustaining activities to develop ways of looking at “regional diversity”.

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.37, no.2, pp.69-84, 1925-02-15 (Released:2010-10-13)

参考文献数

31

著者

武内 寿久祢

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.5, pp.666-667, 1996-10-25 (Released:2009-11-12)

著者

田中 宏幸

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.125, no.5, pp.647-659, 2016-10-25 (Released:2016-11-18)

参考文献数

28

被引用文献数

2 2

---

Atmospheric and anti-electron neutrinos generated inside the solid Earth (geoneutrinos) are potentially powerful tools for imaging the Earth's interior, in order to visualize the spatial distribution of the density of uranium and thorium concentrations. This review is limited to neutrino imaging techniques. Observations of atmospheric neutrinos and geoneutrinos have been reviewed previously and are not discussed here. An elementary introduction to neutrino generation on the Earth and propagation through matter opens the review. After reviewing neutrino tracking methods in the context of today's views of technological developments, the current experimental limits on neutrino imaging are presented. A technique to confront the standard Earth model is discussed in the conclusion. Neutrino imaging of the Earth has been pursued at IceCube. It is fair to mention that it has opened the possibilities of this new elementary particle technique for the first time.

著者

松岡 憲知

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.125, no.1, pp.63-90, 2016-02-25 (Released:2016-03-22)

参考文献数

108

被引用文献数

6 5

---

Following the development of high-resolution imaging, digital elevation models, thermal and hydrological data, and onsite ground information during the early period of the 21st century, the periglacial geomorphology of the Martian surface advanced rapidly. Images can even resolute meter-scale landforms, enabling identification of most periglacial features and analysis of their global distributions and detailed morphologies. This review focuses on progress in research covering permafrost distribution, patterned ground, possible heave and subsidence features, lobate debris forms, and slope-lineated features during the last decade. Most of the Martian high-latitude surface is underlain by ice-rich ground called the latitude-dependent mantle (LDM), which favors permafrost-related features possibly developed under warm-humid conditions during past high-obliquity periods or partially s,till active under the present cold-dry conditions. Thermal contraction cracking is likely to prevail in the LDM, resulting in high-centered, flat-top polygons, possibly underlain by sublimation-type wedges or sand wedges that prevail at high latitudes. The surface patterns change into subdued or peak-top polygons toward the mid-latitudes, probably reflecting long-term sublimation of the LDM. Some researchers attribute stone circles to sorting due to freeze-thaw, but the features are much larger than candidates on the Earth. Small isolated domes with concentric cracks or craters at the top may include pingos, which also prevail at high- to mid-latitudes. Asymmetrical scalloped depressions may result from sublimation or thawing of the LDM, but there is a debate between pole-ward and equator-ward slope retreats. Lobate debris aprons may originate from creep of ice-rock mixtures or debris-covered glaciers, but the distinction between the two origins is unclear, as in the long-lasting debate on terrestrial candidates. Some thin, smaller debris lobes at high latitudes resemble stone-banked solifluction lobes on the Earth, which may indicate the occurrence of seasonal freeze-thaw cycles in the recent past. Time-series images indicate active slope features, including gullies, slope streaks, and recurrent slope lineaes that develop below cliffs. These active features may originate from outflows of brine that thaws far below the melting point of water ice.

著者

菊地 徹

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.67, no.2, pp.94-103, 1958-06-30 (Released:2009-11-12)

著者

鶴岡 弘 大竹 政和

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.111, no.2, pp.256-267, 2002-04-25 (Released:2009-11-12)

参考文献数

34

被引用文献数

2 6

---

We conducted a numerical simulation to clarify the effects of the earth tide on earthquake occurrence. In the simulation, fault planes, having different initial stresses, are loaded by constantly increasing tectonic stress and cyclic stress due to the earth tide. Earthquakes are assumed to occur when the shear stress reached a certain threshold level. The result of the simulation indicates that the tidal effect on earthquake occurrence is strongly controlled by the ratio of stress change rate between earth tide and tectonic stress accumulation; earthquakes concentrate near phase angle 0° (maximum tidal stress) when the ratio is large, and they are distributed with a peak around-90° (maximum acceleration of tidal stress) when the ratio is small. This phase selectivity is very similar to the observations of tidetriggered earthquakes reported so far, and rock failure experiments under cyclic loading, suggesting that our approach may provide an important clue for clarifying the physical mechanism of tidal triggerings of earthquakes. Schuster's test has been widely used for detecting tidal effect on earthquake occurrence. However, it is shown by the numerical simulation that the result of a test strongly depends on the size of a data set when earthquakes have phase selectivity by nature, and that Schuster's p-value is not appropriate to represent the strength of tidal effects. Alternatively, we propose to use α, which is the amplitude of a sine curve fitted to the frequency distribution of earthquakes against phase angle, to evaluate the strength of tidal effects. We also emphasize that the effect of ocean loading is an important component of the earth tide, and cannot be neglected in a study of tidal triggerings of earthquakes.

著者

荒井 章司

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.392-410, 2010-04-25 (Released:2010-07-06)

参考文献数

87

被引用文献数

7 9

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Various characteristics of podiform chromitites, an enigmatic mantle rock member, are reviewed in this article. Chromitites are composed of chromian spinel, with the general formula (Mg, Fe2+)(Cr, Al, Fe3+)2O4, and silicates (mainly olivine). The Fe3+ content is generally very low, being less than 0.1 to all trivalent cations, in mantle chromian spinels. The Mg/(Mg + Fe2+) ratio (= Mg#) changes inversely with the Cr/(Cr + Al) ratio (= Cr#), which increases with an increase of degree of partial melting of mantle peridotites. The Cr# of chromian spinel is generally higher than 0.4 (generally 0.6 to 0.8) in podiform chromitites, varying widely from 0.1 to 0.9 in the mantle peridotite. The podiform chromitite forms pod-like bodies (dimensions of up to 1.5 km × 150 m for an individual pod) with a dunite envelope, totally set within mantle harzburgite. In well-preserved ophiolites, they occur in the uppermost mantle, especially in and beneath the Moho transition zone, which is dominated by dunite. The Cr# of chromian spinel is relatively low (0.4 to 0.6) around the Moho transition zone, and high (>0.6) at deeper levels in the mantle section. Chromitites are denser and less anisotropic in Vp than peridotites, and the Vp is 8.5 to 9 km/sec depending on the proportion of chromian spinel, and higher in the former than in the latter.  The podiform chromitite has been interpreted to be one of melt/rock interaction products within the uppermost mantle harzburgite; hybridization of relatively Si-rich melt formed by the breakdown of orthopyroxenes of the wall harzburgite and subsequently supplied primitive melt cause oversaturation in chromian spinel, giving rise to formation of chromitite with a dunite envelope. The fractionated melt leaving high-Cr# podiform chromitite is possibly of arc-magma affinity. Chromitites with low-Cr# (0.4 to 0.6) chromian spinel can be in equilibrium with MORB. Recently found ultra-high pressure minerals, such as diamond, moissanite, Fe-silicides and Ni-Fe-Cr-C alloys, within chromian spinel of podiform chromitites make the genetical history of chromitites highly enigmatic. A new story, which incorporates the genesis and involvement of these highly reducing, ultra-high pressure minerals, is required.

著者

西野 寿章

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.298-314, 2014-04-25 (Released:2014-05-16)

参考文献数

46

被引用文献数

3

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The purpose of this paper is to clarify the history and the characteristics of electric utility companies in Tokyo. In 1887, the first electricity supply company in Japan was established in Tokyo. In 1933, there were 818 electric utility companies. Before World War II, two or more electricity supply companies supplied one region, and there was tough competition to supply electricity to the Tokyo area. In 1938, the principle of free competition was replaced by nationwide management by the pre-war military government. Tokyo Electric Power Company was established in Tokyo by the Potsdam government ordinance in 1951, and the right to supply electricity to a region was limited to one company. Disproportionate electricity demand and amount of power generated is a historical characteristic of electric utility companies operating in Tokyo. The rate of self-sufficiency of electricity in Tokyo was 15 percent in 1931, and it was three percent in January 2012. The power generation and electric supply system began to be discussed after the nuclear plant disaster caused by a major earthquake on March 11, 2011 at Fukushima. In August 2011, the Tokyo Metropolitan Government Office began to examine constructing a large-scale power plant fueled by natural gas.As the population of Japan decreases, revenues will decline. Before World War II, Tokyo City's managed electric utility obtained high earnings constantly. These high earnings were a very important and stable source of income for the local government. The system of the electric utility companies in Japan before World War II could provide a model for a reorganized electricity supply system in the future.

著者

國松 豊

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.6, pp.798-815, 2002-12-25 (Released:2009-11-12)

参考文献数

102

被引用文献数

2 3

---

The human lineage is a branch of the huge evolutionary tree of the Hominoidea, which today includes ourselves, chimpanzees, gorillas, orangutans, and gibbons. All extant hominoids, except for the single world-wide species Homo sapiens, are now endangered and restricted in their distribution to tropical/subtropical forests of Africa and Southeast Asia. However, hominoids were once a more flourishing group millions of years ago. In the Miocene, there were various kinds of hominoid primates, and their distribution was much wider than today, from the southern tip of Africa through Arabia, to Europe in the west and through India to China in the east. It is from this great diversity of Miocene hominoids that the earliest human ancestors emerged, probably during the Late Miocene. The first part of this article provides readers with general information about extant hominoids. The second part is devoted to Miocene fossil hominoids with emphasis on African fossils. Although the main subject of this article is fossil hominoids, some recent findings of early hominids are also mentioned to at the end.

著者

河合 研志 内出 崇彦

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.128, no.3, pp.465-475, 2019-06-25 (Released:2019-07-11)

参考文献数

23

被引用文献数

1

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Teaching materials on determining epicenters using P-wave lateral polarity data were produced. These materials are intended for use in secondary and advanced education and only require inexpensive tools such as a ruler and a protractor; they do not require specialized software or devices. The materials consist of PDF files containing three-component waveform data before and after P-wave arrivals for 929 small events recorded at Hi-net stations in the Hida region, central Japan, from February 1 to April 30, 2011. A P-wave lateral polarity analysis using the two horizontal components provides information on seismicity in the Hida region before and after the March 11, 2011 off the Pacific coast of Tohoku Earthquake. Students can discuss temporal changes in the underground stress state based on their analyses. Depending on the grade and science education level of students, the time-series waveform data allow them to conduct additional exercises such as error analyses and epicenter determinations using S–P differential travel time, as well as geophysical interpretations of results.

著者

早川 裕一 松倉 公憲

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.4, pp.521-530, 2003-08-25 (Released:2009-11-12)

参考文献数

26

被引用文献数

7 11 1

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The mean recession rate of Kegon Falls is examined, estimating original location and age. Two locations (LI and LII) at which the waterfall originated are estimated based on the distribution of Kegon lava, while the age of origination is considered to be the same as that of the Kegon lava eruption, i.e., 20, 000 years ago. Two values of the mean recession rate obtained are 0.018 m/y for the case of LI and 0.10 m/y for the case of LII. On the other hand, the recession rate can be evaluated, as an order estimation, using the empirical equation of the authors (Hayakawa and Matsukura, Earth Surf. Process. Landforms, 28, 2003), which shows relationships between the recession rates of waterfalls and the ratio of the erosive forces of rivers to bedrock resistance. The values of parameters used in the index of force/resistance ratio are obtained from existing data and field measurements for Kegon Falls. Substituting them into the equation, the recession rate is calculated to be in the order of 0.009-0.019 m/y. This result suggests that the recession rate for the case of LI is suitable for Kegon Falls.