著者

三好 寿 牧野 清

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.25, no.1, pp.33-43, 1972

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The lowlands of southwestern islands of Okinawa are dotted with many blocks of coral which were quarried and conveyed from the reef on the floor of the sea, by the giant tsunami of April 24, 1771. We investigated the distribution of blocks in Ishigaki Island. We chose the third biggest block in this island, the approximate weight of which is 750 tons. It lies some 2.5 kilometers away from the nearest coast line, and its location reaches some 30 meters above sea level. We pierced a tunnel through the base of this huge block, which is the hardest to be imagined to have been conveyed by the tsunami, and demonstrated that this block takes no root. In the opinion of some persons, these blocks are the negro heads of the erosion type. But our tunnel crushed down this opposition. One is apt to feel that this capacity of the tsunami is rather fantastic in view of wave dynamics. But, for example, the giant wave observed in Lituya Bay (Alaska) in 1958, the energy of which was ascertained accurately, could have conveyed the supposed coral pillar whose cross section is some 27.3mm<SUP>2</SUP>, to the same position of the above-mentioned block, losing only 0.73% of its wave energy.<BR>Then we considered the action of the tsunami of 1771 upon the tied-island called Funakuy&acirc; in Ishigaki Island. We confirmed that it is traditionally said that the northern part of this island has never been isolated from the main part of the island.

著者

相田 勇

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.28, no.4, pp.449-460, 1975

被引用文献数

3

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On May 21, 1792, a gigantic collapse of Mt. Mayuyama in Shimabara Peninsula, Kyushu, occurred. Following this event, a severe tsunami of about 10 meters in height was generated by the landslide and attacked the coast of Ariake-kai, killing more than 14, 500 persons. Many historical documents tell us the phenomena of this tsunami in fair details, so that we attempted to reconstruct a numerical model of the tsunami consistent with the historical data. In the numerical computation, a finite difference method with a leap-frog system is adapted, and two kinds of source input are tried; one is the prescrived water mass transport normal to shore line and the other the vertical displacement of sea bottom. When the transport of 18, 000m³/min (current speed-20m/sec) per unit length of shore on the center line of landslide area is assumed to be continued during 2 to 4 min, the computed waves agree fairly well with the real tsunami behaviors, the height of tsunami in various places along the coast and the order of the maximum crest in the sequence of a wave train. Therefore, it seems probable that the extraordinary flow of water normal to the shore occurred by some physical mechanisms of the mountain collapse.<br>The energy of this tsunami is estimated to be about 5&times;10¹⁹erg, and this is about 1/100-1/1000 of the available potential energy of the slided material due to the collapse of the mountain. It is significant that the tsunami energy is several times larger than that of the 1968 Hyuganada Earthquake (<i>M</i>=7.5). The wave spreaded over a wide area and gave distructive damages to the coast more than 120km on both side of Ariake-kai.

著者

羽鳥 徳太郎

出版者

公益社団法人 日本地震学会

雑誌

地震. 2輯 (ISSN:00371114)

巻号頁・発行日

vol.51, no.2, pp.203-210, 1998-10-15

参考文献数

19

被引用文献数

1

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The generating frequency of the North-West American tsunamis is relatively lower than that of the South American region, but there are historical records of a large tsunami accompaning with the January 1700 earthquake (<i>M</i> 9) in the Cascadia subduction zone (SATAKE <i>et al.</i>, 1996). In the present paper, tsunami magnitudes on the Imamura-Iida scale, <i>m</i>, are investigated by using the diagram of wave-height attenuation with distance. The regional characteristics of tsunami magnitudes are discussed in relation to earthquake magnitudes, <i>M</i>_s, during the period from 1899 to 1997. The tsunami magnitudes in the South-East Alaska to Canada region are nearly normal compared to earthquakes with similar size in the other Pacific regions, and the 1899 Yakutat tsunami being <i>m</i>=3 is the largest. The magnitude values in the California region are mostly <i>m</i>=0 or less (amplitude: 50-100cm), but those of a few tsunamis vary by the faulting mechanism. For example, the magnitude value of the 1906 San Francisco tsunami accompaning with a strike-slip earthquake (<i>M</i>_s=8.3) is <i>m</i>=-4. On the contrary, that of the 1927 Lompoc tsunami caused by a high-angle thrust earthquake (<i>M</i>_s=7.0) is <i>m</i>=1, and this tsunami was observed in Hawaii and Japan. According to the epicenter distribution of the earthquakes (<i>M</i>_s&ge;6.5) since 1812, a seismic gap exists at the segment of 700km off the Washington to Oregon states. It should be considered a region of relatively high tsunami risk.

著者

弘瀬 冬樹 前田 憲二

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.70, pp.21-40, 2017-05-10 (Released:2017-09-07)

参考文献数

32

被引用文献数

1 1

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Frequency-magnitude distributions are generally expressed by the Gutenberg-Richter (G-R) law. However, frequency-magnitude distributions are sometimes a convex-upward curve rather than a straight line, departing from the G-R law. An η value originally introduced by Utsu (1978) is an indicator that represents the degree of deviation from the G-R law. We investigate η values before and after six M7-9 class mainshocks off the Pacific coast of eastern Japan. The η values tend to become small (i.e., the distribution deviates from the G-R law) before the mainshocks, and then increase (i.e., recovering to the G-R law). Taking this characteristic into account, we suggest a simple and challenging earthquake forecast model based on η values. Probability gain of the optimized forecast model by a retrospective test becomes 2.24-3.03, and the alarm rate and the truth rate become 100% and 0.14-0.47%, respectively. According to the result of the forecast model applied to the latest seismicity, we should pay attention to seismicity off the coast southeast of Kanto district.

著者

斎藤 正徳

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.17, no.1, pp.40-55, 1964-03-25 (Released:2010-03-11)

参考文献数

57

著者

山口 林造

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.17, no.1, pp.28-39, 1964-03-25 (Released:2010-03-11)

参考文献数

66

著者

竹内 均

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.17, no.1, pp.24-27, 1964-03-25 (Released:2010-03-11)

参考文献数

33

著者

佐藤 泰夫

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.17, no.1, pp.14-23, 1964-03-25 (Released:2010-03-11)

参考文献数

37

著者

加藤 祐三 森 宣雄

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.48, no.4, pp.463-468, 1996-03-12 (Released:2010-03-11)

参考文献数

10

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The records on a disastrous earthquake of July 25, 1882, southern Okinawa Island were discovered for the first time from nine archives. The most important are: “Okinawa-nisshi” written by Hatakeyama, a secretary of prefectural governor Uesugi; “Ryukyu-iki-nisshi” written by Ozaki, high official, dispatched from the central government to inspect a political situation in the Okinawa Prefecture; the official diary of the Okinawa Prefecture; and, the official document from the Okinawa Prefecture to the central government. Synthesizing these records, the earthquake happened between 1 and 2a. m., on July 25th, 1882, and aftershocks were intermittent for seventy days following. While there were no casualties, 500 stone walls were broken in Naha City. Analysing these records, the seismic intensity of this earthquake was probably 5. The reason why this earthquake was not discovered for about one hundred years is, firstly, the records of “Kyuyo”, an official document of the Ryukyu Kingdom, had already stopped, because the Kingdom was ruined three years before the earthquake, and secondly, the Japanese earthquake observation system was insufficient at the time of the earthquake.

著者

飯田 汲事

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.24, no.3, pp.266-274, 1971 (Released:2010-03-11)

参考文献数

32

被引用文献数

2 2

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There have been developed a number of relations between seismic wave energy E and the magnitude M of an earthquake. The general form of the relation is written as logE=α+βM. in which α, β are constants and M is the surface-wave magnitude. A number of relations were presented as given in Table 1 where α and β are listed. The relationship between α and β seems to keep linearity as shown in Fig. 1. This relation can therefore be expressed as α=(26.10±0.91)-(9.60±0.72)β for 5.3≤M≤8.5 (1) α=(19.11±0.70)-(4.59±0.40)β for -2.1≤M≤5.3 (2) An energy-magnitude relation for large earthquakes having magnitude larger than 5 seems to be different from that for small earthquakes having magnitude smaller than 5.The lines expressing (1) and (2) intersect at the point α=12.66, β=1.40. Thus, a new magnitude-energy relation which is appropriate for both large and small earthquakes is obtained as logE=12.66+1.40M. By using the relations between α and β in (1) and (2), seismic efficiency factor f was obtained as 0.04-0.90 from some examples.

著者

渡辺 偉夫

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.21, no.4, pp.293-313, 1969-02-25 (Released:2010-03-11)

参考文献数

30

被引用文献数

2

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Table of tsunamis which occurred in and near Japan was prepared. The table consists of two parts. One part (Table 1) is the table of tsunamis caused by earthquakes, vocanic eruptions and landslides which occurred in and near Japan. Another one (Table 2) is the table of tsunamis which occurred in the Pacific Ocean and additionally invaded Japan and its vicinity.1) Table 1.The contents of the table are:a) Sequential numberb) Date in the Christian and Japanese Calendar (Time in Japanese Standard Time)c) Location of tsunami source or epicentral region together with longitude, latitude and depth of hypocenterd) Magnitude of earthquakee) Grade magnitude of tsunami by Dr. A. IMAMURA and Dr. K. IIDAf) Description of earthquake and tsunami.Magnitude of earthquake, and longitude, latitude and depth of hypocenter were taken from the “Rika-nenpyo (1968)”, the “Catalogue of major earthquakes which occurred in and near Japan, supplementary volume No. 1 (1958), No. 2 (1966) and No. 3 (1968)” and the “Zisin-geppo (1968)”.2) Table 2.The contents of the table are:a), c) and f) The same content as the Table 1b) Date in the Christian Calendar (Time in Greenwich Mean Time)e) Grade magnitude of tsunami occurred in the Pacific Ocean and invaded Japan and its vicinity.Magnitude of earthquake, and longitude, latitude and depth of hypocenter were taken from the “Seismicity of the Earth and Related phenomena (1954)” and the report of the U. S. Coast and Geodetic Survey.

著者

宇津 徳治

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.31, no.2, pp.129-135, 1978-07-31 (Released:2010-03-11)

参考文献数

7

被引用文献数

2 1

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Discrimination of foreshock sequences from earthquake swarms is an important problem in earthquake prediction. In this paper, the magnitudes of the largest, the second largest, and the third largest shocks in an earthquake swarm or foreshock sequence are denoted by M1, M2, and M3, respectively, and Japanese shallow earthquake swarms and foreshock sequences (with M1-M2≤0.6 and M1≥5.0 for 1926-64 or M1≥4.5 for 1965-77) are classified according to the values of M1-M2 and M1-M3, and the time sequence of the shocks of M1 and M2. If we select the earthquake swarms and foreshock sequences satisfying the following conditions, the highest proportion of foreshock sequences to earthquake swarms is achieved. The conditions are: (1) 0.4≤M1-M2≤0.6, (2) M1-M3≥0.7 (or M3 is too small to be determined), and (3) the shock of M2 precedes the shock of M1. The numbers of foreshock sequences and earthquake swarms selected under these conditions are 10 and 17, respectively, while the total numbers of foreshock sequences and earthquake swarms are 13 and 232, respectively. It is confirmed that the above criterion is also effective, if it is used during the course of an earthquake sequence.

著者

細山 謙之輔

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.5, no.2, pp.45-48, 1952-06-15 (Released:2010-03-11)

参考文献数

6

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Secular change of latitude was compared with those of some geophysical phenomena. It was found that there existed an intimate correlation between the secular displacement of the earth's mean pole and the change of height of mean sea levels of the Atlantic Ocean and Pacific Ocean.On the other hand, the Chandlerian amplitude and period showed a parallel change with the amplitude of tidal variation of latitude.In both cases a geoid pulsation may be postulated.

著者

翠川 三郎

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.47, no.3, pp.333-340, 1994-10-14 (Released:2010-03-11)

参考文献数

54

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In order to deepen understanding of the characteristics of near-field ground motion, case histories of upthrow of objects during 21 earthquakes are reviewed. The fault distance to the site where the upthrow was observed becomes larger with increase of the earthquake magnitude. The area where the upthrow was observed roughly corresponds to that of the J. M. A. intensity VII which is X or greater in the M. M. scale. The upthrown objects are boulders, stone mouments, human bodies, small structures and wooden houses, with limitation in size. In case of the boulder, one on a shallow socket of surface soil and with the diameter of approximately 50cm tends to have a large displacement. These facts may suggest the soil-object interaction system with a limited vibration period causes a large response of the object and the resulting upthrow under strong shaking of the M. M intensity X or greater.

著者

大滝 壽樹 吉田 康宏 神定 健二

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.66, no.2, pp.27-30, 2013-09-19 (Released:2013-10-16)

参考文献数

6

著者

杉崎 隆一 志知 龍一

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.31, no.2, pp.195-206, 1978-07-31 (Released:2010-03-11)

参考文献数

21

被引用文献数

1 1

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The utility of the ratios of He/Ar and N2/Ar of fault gases as an earthquake precursor was discussed and examined. The ratio of helium to argon produced in the lithosphere remains rather constant (≅10) for the past several hundred million years irrespective of rock types. The ratio in the lithospheric air amounts to 105 times higher than that of the atmospheric air (5.7×10-4). The lithospheric air released by the formation of cracks and migrated by the stress in rocks prior to earthquakes, therefore, can be easily detected by means of the ratio. The N2/Ar ratio is also expected to be a useful parameter of a lithospheric air, because the ratio in natural gases and volcanic gases is generally higher than that of the atmospheric air. These ratios do not change a dilution process by other gases such as CH4 and CO2, and accordingly the ratios are more useful parameter of lithospheric air than a single element. The ratios of He/Ar and N2/Ar are gas-chromatographically measured without vacuum processes, temperature and pressure corrections and other complicated treatments.The result of successive measurement, since 1976, of the ratios in a fault at Inuyama Crustal Movement Observatory, Nagoya University, indicated that the ratios continuously fluctuated and the peak in the variation of the ratios of He/Ar and N2/Ar appeared prior to the most felt earthquakes in Nagoya (M≥4). The peaks of He/Ar preceeded those of N2/Ar for all events, which might be attributed to the difference in diffusion velocity of He and N2 through capillary cracks. The time lag of N2/Ar peak in case of the large earthquake is longer than that of the others. These features emerged in the variation of the ratios can possibly provide a practical mean of predicting earthquakes.

著者

岡村 行信

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.71, pp.185-199, 2019

被引用文献数

5

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<p>An active fault map of Japan Sea was compiled based mainly on bathymetric data and seismic profiles that cover shelves to slopes between 4 to 150 km from the coasts of Japan Islands. The seismic profiles using air guns as seismic sources revealed active faults that have slipped during the last 104 to 106 years. In addition, high-resolution seismic profiles using a boomer as the seismic source were obtained along seaward extensions of onshore active faults in shallow sea areas less than 150 m below sea-level, and activity of the faults during the last 104 years was identified. In northeastern Japan Sea, to the northeast of the Noto Peninsula, many reverse faults accompanying large hanging wall anticlines (>750 m uplift) are concentrated in two N-S trending fault zones along the Okushiri and Sado ridges. Earthquakes larger than M 7.5 in 1940, 1964, 1983 and 1993 occurred in these fault belts. Three NE-SW trending fault zones cross the N-S trending fault zones and disrupt the structure of the N-S fault zones. In the offshore area from the Noto Peninsula to the Tango Peninsula, active reverse faults accompanying smaller hanging anticlines (<375 m uplift) are identified in a zone trending subparallel to the coasts. In addition, NW-SE to N-S trending strike-slip and reverse faults extend from onshore to offshore. In the offshore area to the west of the Tango Peninsula, E-W and NW-SE trending active strike-slip faults are identified. The former faults developed in about 40 km wide zones sub-parallel to the coast, and the later faults are located landward of the E-W trending fault zones. Some of the later faults are extensions of onshore active faults. Unknown active faults may exist in shallow sea area along coasts where have not been thoroughly investigated. Displacements of the faults during the last 106 years are large in northeastern Japan Sea and decrease to the southwest, while slip rates of these faults during the last 104 years are inferred to have smaller differences. These faults have the potential of future earthquakes, while there is not enough data to evaluate the activities of these faults.</p>

著者

吉田 明夫 小林 昭夫 塚越 利光

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.58, no.4, pp.401-406, 2006-03-31 (Released:2010-03-11)

参考文献数

23

被引用文献数

1

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Areal strain increased noticeably in the region around the northern boundary of the Izu Peninsula in September to December 2000 when a lot of low-frequency earthquakes occurred beneath Mt. Fuji. In the same time the seismic activity in eastern Yamanashi Prefecture became low. Since increase of the areal strain indicates reduction of the pushing force of the colliding Izu block, the decrease of seismicity in eastern Yamanashi Prefecture is easily understood. Further, because diminution of the tectonic stress beneath Mt. Fuji implies reduction of the confining pressure in the magma reservoir, we think it is probable that degassing took place in the magma to build up high pressure in the focal region near the chamber which caused the remarkable activity of the low-frequency earthquakes. We suggest the noticeable increase of the areal strain in late 2000 might be produced by a mechanical separation of the Izu block from the Philippine Sea plate or detachment of the crust of the Izu block as proposed by Seno (2005).

著者

平松 良浩 小阪 大

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.65, no.3, pp.251-254, 2013

被引用文献数

1

著者

島津 康男

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.8, no.2, pp.67-74, 1955-10-20 (Released:2010-03-11)

参考文献数

4

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Chemical structure of the earth's mantle is discussed under the assumptions that (1) chemical equilibrium and hydrostatic equilibrium are attained; (2) it is isothermal and incompressible. Based upon these assumptions, the distribution of chemical elements would be controlled by differences in their chemical affinities as well as by gravitational separation due to their density differences. Calculation of the equilibrium distribution of FeO-MgO-Fe-SiO2 system, it is concluded that FeO would increase with depth, reach maximum at a depth of several hundred kilometers, and then would decrease toward the earth's center. This result suggests the origin and the physical property of Jeffrey's 20° discontinuous layer.