著者
阿部 壽 菅野 喜貞 千釜 章
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.43, no.4, pp.513-525, 1990-12-24 (Released:2010-03-11)
参考文献数
21
被引用文献数
4 5

It is known that great Sanriku tsunamis sometimes hit the Sendai Plain in the north part of the Honshu Island in Japan. Among those great tsunamis, the field investigation had been rarely carried out about the tsunami of July 13th, 869 (11th year of the Jogan Era) because of the lack of the materials of old documents. We carried out the field investigation of the height of this tsunami in the Sendai Plain on the basis of the archaeological view and the sedimentologic examination. The former method is based on the archaeologist's judgement whether historic relics have the trace buried by the running water or not. We estimated the inundated area from the result of the survey for the 8 points in the Sendai Plain. In the latter method, we dipped the test pit and observed the soil layer of the side wall minutely to find the sand layer being supposed to be carried by the tsunami from the dune. Moreover to analyze the character of the sand layer, we made the physical examination, the chemical analysis and the measurement of the age by 14C method. From the results of these investigations, the height of the Sanriku Jogan 11 earthquake-tsunami (A. D. 869) is estimated as 2.5-3m at the point 3km from the coastline in the Sendai Plain. Finally we checked it with the social and geographic circumstances at that time, and we got the result that the estimated height is not inconsistent with the record of this tsunami.
著者
三浪 俊夫 久保寺 章
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.30, no.1, pp.73-90, 1977-04-05 (Released:2010-03-11)
参考文献数
19

An earthquake swarm started its activity in the northern somma of the Aso caldera on January 20, 1975. In the course of the earthquake swarm activity, on January 23, an earthquake of magnitude 6.0 representing the largest one among the whole earthquake swarm took place. After this earthquake, the activity of the earthquake swarm declined gradually until the end of January. By using available data obtained from all the seismological stations in the Kyushu district, 120 foci of these earthquake swarm were determined with fairly a high accuracy.Analysing the time variation of the frequency of earthquakes, the migration of their foci, the variation of b-values, and so on, it was found that these features seen in the earthquake swarm were having quite a similar character in the fracturing of the stressed rocks.1) The b-values showed fairly a large differrence in the two periods, i. e. before and after the largest earthquake. Before the earthquake, b=0.73 while after the earthquake b=1.01.2) The series of the earthquake swarm activity can be divided into 6 stages, from the consideration of the migration of the earthquake foci or their characters. The temporal change in the spatial distribution of these foci was noteworthy. In the early stage of the activity a void space (seismicity gap) was observed in the central part of the area in which many foci were distributed. In the next stage, small earthquakes began to take place inside of the above mentioned void space, then at last the largest earthquake occurred at the edge of the void space.3) A volume of the void space may be taken to be 1.8×1017cm3 from the locations of foci during the stage II and the ultimate stress energy that can be stored up in the void space until a break-down takes place can be estimated to be 5.65×1020 erg. According to the relation between the energy of an earthquake and its magnitude i. e. log E=11.8+1.5M, the magnitude of the largest possible earthquake M=5.97 is obtained. This value agrees with the magnitude which has been determined from the maximum amplitude on the seismograph of the above mentioned largest earthquake (M=6.0) among the whole swarm.4) Considering the migration of the earthquake foci, it may be concluded that this earthquake swarm activity have not been related to a volcanic activity of the Volcano Aso.
著者
多田 堯
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.37, no.3, pp.407-415, 1984-09-25 (Released:2010-03-11)
参考文献数
28
被引用文献数
1 11

The repeated triangulation surveys have revealed the conspicuous N-S extentional strain field in the central Kyusyu. This strain field has been caused by the horizontal crustal movement that the triangulation stations in both the sides of the Beppu-Shimabara Graben have moved away each others to the N-S direction. The Beppu-Shimabara Graben strikes across the central Kyusyu to the E-W direction. The gravity anomaly, the seismological data and other geotectonic data support the idea that the Beppu-Shimabara Graben is a rift of the crust and the north-eastern terminal part of the Okinawa Trough which is the active back arc basin of the Ryukyu Arc and is spreading to the N-S direction. Therefore, it is concluded that the N-S extentional crustal deformation in the central Kyusyu has been caused by the rifting and the spreading of the Okinawa Trough. In other words, the Kyusyu is rifting and spreading to the N-S direction along the Beppu-Shimabara Graben. The spreading ratio is estimated to be about 15mm/a from the horizontal crustal deformation.
著者
高山 博之 吉田 明夫
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.57, no.4, pp.409-418, 2005-03-20 (Released:2010-03-11)
参考文献数
12

When a larger earthquake than the preceding ones occurs successively in a clustered activity, it seems a further larger earthquake is apt to be observed afterwards (Yoshikawa et al., 2000). We investigate alarm rate, success rate, and probability gain for the occurrence of an earthquake with M5 or larger in such sequential activities. We use the JMA catalogue during the period from 1995 to 2000. First, we select out clusters of shallow (depth≤30km) earthquakes withM≥2.5 in and around Japanese islands. We name the first earthquake in a cluster E0, and the one larger than E0 that occurs first in the succeeding activity E1, and term such clusters that contain E1 earthquake E1-class clusters. E2 earthquake and E2-class clusters are defined in the similar way. We calculate the alarm rate, the success rate and the probability gain, when M≥5 earthquakes are forecasted using E1-class clusters and E2-class clusters, respectively. We also examine how the alarm and success rates change when criterion of selecting clusters and upper limit of distance and time interval are varied. It is shown that, for E1-class clusters, the alarm rate is 24 to 30% and the success rate is about 5%. For E2-class clusters, the alarm rate is 10 to 15% and the success rate is 10 to 14%, and we get a value as large as 5702.2 for the probability gain in the best case that both the criterion and the upper limit of selecting clusters are set to be 5km-5days. The large values of the alarm and success rates and the probability gain indicate that the algorithm for forecasting M5 earthquakes proposed in this paper is practically effective as well as statistically significant.
著者
川辺 岩夫
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.44, no.Supplement, pp.341-364, 1991-07-24 (Released:2010-03-11)
参考文献数
98
被引用文献数
3

Hydro-geochemical anomalies associated with large earthquakes are reviewed and discussed from the viewpoints of (1) the response of confined groundwater to minute deformations of crustal rocks, (2) ground-water anomalies related to earthquake source mechanisms, (3) origins of groundwaters and dissolved gases in them, and (4) factors to cause groundwater gas anomalies.Theoretical models for deformations of water-saturated porous or cracked rocks under the undrained condition indicate that compressive and extensive stress changes induce increasing and decreasing changes in the pore water pressure, respectively. The pore pressure change is to be the same order of the external stress change, but the maximum change of pore pressure cannot exceed the stress change. These are consistent with observed responses of confined groundwaters to the earth tides.Coseismic groundwater anomalies accompanied by the 1946 Nankaido earthquake and the 1923 Great Kwanto earthquake are directly related to their residual fields of megathrusting faults. Preseismic groundwater anomalies of these great earthquakes commonly suggest that megathrusting fault motions began to start preceding main seismic events.Chemical compositions of groundwater gases are controlled by admixing of the dissolved atmospheric air with the subsurface gases enriched in CH4, He and others. Groundwater gas anomalies can be described by the change in mixing ratio of the two different gases and/or by the compositional change of the admixing subsurface gas itself. Such an admixing process could be affected by anomalous pore pressure distributions induced by the deformation of crustal rocks related to earthquakes. H2 gas anomalies are distinctive among subsurface gas anomalies reported so far, but the origins are not fully understood. The characteristics of H2 anomalies are discussed.
著者
溜渕 功史 山田 真澄 Stephen WU
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.67, no.2, pp.41-55, 2014-09-30 (Released:2014-11-25)
参考文献数
25
被引用文献数
3 4

The extremely active seismicity after the 2011 off the Pacific Coast of Tohoku Earthquake (Tohoku Earthquake) caused serious issues for the Earthquake Early Warning (EEW) system in Japan. Multiple concurrent earthquakes generated many false alarms due to the failure of correctly determining the source location. In this study, we propose a method to distinguish multiple concurrent events for EEW. We used the outputs of a B-delta method and principal component analysis, together with P-wave arrival times and amplitudes of triggered stations. The information of non-triggered stations is also used to constrain the locations. We constructed a likelihood function using the source parameters and solved this optimization problem using the particle filter. The appropriate choice of a likelihood function improves the accuracy of the location determination, and the probabilistic framework evaluates the uncertainty of the hypocenters. We applied this method to 72 events for which warnings were issued after the Tohoku Earthquake. The performance of EEW was greatly improved, reducing the false alarms from 22 to 0. The percentage of inaccurate warnings was also reduced from 66% to 6%.
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.30, no.2, pp.179-185, 1977-08-05 (Released:2010-03-11)
被引用文献数
1 6

Two kinds of probabilities p1 and p2 are considered in connection with the earthquake prediction, p1 is the probability that a prediction will be successful, and p2 is the probability that an earthquake will be predicted. Both “prediction” and “earthquake” have been defined by some criteria X and Y, respectively. The status of the prediction based on each observational element can be indicated by a point on the p1-p2 plane. The effectiveness of the prediction is related to p1 and p2 by an equation in the form E=p2(a-b/p1)-c where a, b and c are constants. If two or more observational elements are considered, p1 and p2 for the combined elements are calculated from p1 and p2 for each element under some assumptions. Formulas for such calculation have been derived. In these formulas the probability p0 that a random prediction (under criterion Y) will be successful plays an important role. For example, if a prediction is done when precursorlike anomalous phenomena are observed for two independent elements A and B, the probability of successful prediction is given by p1(A ∩ B)=1/1+(1/Ap1-1)(1/Bp1-1)/(1/p0-1) where Ap1 or Bp1 is the p1-value for element A or B alone. The effectiveness of the multielement prediction is discussed by using these formulas.
著者
武村 雅之
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.46, no.4, pp.439-455, 1994-03-14 (Released:2010-03-11)
参考文献数
29
被引用文献数
1

Aftershock activities for two days after the 1923 Kanto earthquake is reinvestigated from the data of S-P time, maximum amplitude, and its period, which are newly measured on the records at the Gifu observatory. 34 aftershocks with magnitude M from 5.0 to 7.5 are identified on the records. According to locations of epicenters of aftershocks inferred from the S-P times, most of large events concentrated in the vicinities of western or eastern ends of the rupture area of the main shock. The first aftershock activity started in the western region immediately after the main shock at about 12:00 on the 1st of September and included two M=7 class events, whose magnitudes are newly determined from maximum amplitudes in vertical component of these records. At about 12:40, aftershocks began to occur in the eastern region. The next activity began at 13:00 in the western region again. From 17:00 on the 1st to 11:00 on the 2nd of September, the activity was quiet. The largest aftershock of M=7.5 and its related events occurred in the eastern region after this quietness. Then, the activity returned to the western region again at about 21:00. It is found that the number of M≥6 aftershocks is 16 for two days, which is meaningfully larger than that for the other M=8 class events in and around Japan.The natural period of the vertical component of the seismograph was about 1s, while those of the horizontal components were about 5s. Therefore, the ratio γ of maximum amplitude in vertical component to those in horizontal components is used as a parameter which show a frequency characteristic of seismic waves from each aftershock. All the aftershocks in the eastern region have low-frequency characteristics, which show smaller γ values, comparing with those in the western region. We also found some aftershocks of which wave forms are similar to those of recent events occurring in the same region. These results indicate that the aftershock activities included the same type events as we can find in the recent seismicity and suggest that the locations of epicenters of the aftershocks inferred in the present study are proper.
著者
奥村 晃史 井村 隆介 今泉 俊文 東郷 正美 澤 祥 水野 清秀 苅谷 愛彦 斉藤 英二
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.50, no.appendix, pp.35-51, 1998-03-31 (Released:2010-11-17)
参考文献数
25
被引用文献数
7

The Itoigawa?Shizuoka tectonic line active fault system (ISTL) is one of the longest and the most complex active fault systems on land in Japan with very high activity. The system comprises the northern (55 km long east dipping reverse faults), the middle (60 km long left-lateral strike-slip faults), and the southern (35 km long west-dipping reverse faults) sections. The estimates of the average slip rate range 2 to over 10 m/103 yr in the system. This high slip rate and probable quiescense of the system exceeding 1150 years indicate the possibility of a surface faulting event in the near future. Since historic and instrumental records of seismicity along the ISTL is very poor, geological study on the paleoseismology of the ISTL has an important clue to evaluate the long-term seismic risks of the fault zone. In 1995 and 1996 the Geological Survey of Japan opened six exploratory trenches in the fault system and the results from the three in the northern section are reported in this paper. The Hakuba trench on the Kamishiro fault brought four earthquake events since 6738 BP (dendrocorrected radiocarbon age in calendar year) with the average recurrence interval to be between 1108 and 2430 years. The last event here postdates 1538 BP. The Omachi trench exposed the last event after 6th to 7th century AD and before 12th century at the latest, Only one event after 3rd to 4th century AD was identified in the Ikeda trench. The timing of the last event from each trench is between 500 and 1500 BP, which interval coincides with the timing of the last event in the middle section as well as the 841 AD or 762 AD earthquake reported in historical documents. The dating of the upper age limit of the last event is not precise enough to correlate the event with any of known earthquake. The recurrence interval of the northern section, however, is significantly longer than that of the Gofukuji fault. The difference in the recurrence time from one section to another is concordant with the difference in the apparent slip rate.
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.28, no.3, pp.303-311, 1975-10-10 (Released:2010-03-11)
参考文献数
13
被引用文献数
1 1

A correlation has been found between intermediate earthquakes in Hida (the region around the city of Takayama) and shallower earthquakes in central Kwanto (the region around the city of Tokyo). Among 61 earthquakes of M≥5.5 in central Kwanto during the 51 years from 1924 through 1974, 37 earthquakes occurred in the one-year periods centered by the times of 16 earthquakes of M≥5.0 in Hida. The probability that 37 or more earthquakes in central Kwanto occur during those periods (total length=14.46 years) is 1.5×10-7, if the Kwanto earthquakes are distributed randomly in time. It seems impossible that the smallness of this probability is wholly attributed to some effects other than the true correlation, such as the selection of data, the clustering of earthquakes, etc. The correlation suggests the mechanical connection between the two seismic regions, which belong to the same segment of the Pacific plate underthrusting at the northeastern Japan arc.
著者
武村 雅之 諸井 孝文 八代 和彦
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.50, no.4, pp.485-505, 1998-03-13 (Released:2010-03-11)
参考文献数
96
被引用文献数
1 2

Two types of earthquakes have occurred in and around Japan, which have resulted in severe damages. They are inter-plate earthquakes in subduction zones around the Japan Islands, and intra-plate earthquakes in the upper crust beneath the mainland of Japan. The faults associated with intra-plate earthquakes usually exist within a depth of 20km. Six intra-plate earthquakes causing a toll of more than 1, 000 lives have occurred since the end of the 19th century. The faults responsible for these events were estimated from the trains of surface fault breaks and the measured crustal deformations. Three intra-plate earthquakes with magnitude M larger than 7, which killed more than 200 people, have also occurred in the same period. Their causative faults have also been estimated. Many reports of damage surveys of the above nine intra-plate earthquakes were examined to investigate conditions necessary for generating strong ground motion with seismic intensity I=VII (very disastrous) in the Japan Meteorological Agency (JMA) scale, and to elucidate characteristics of strong ground motion with I=VII. According to the original definition of the JMA scale, I=VII (very disastrous) corresponds to “Collapse of more than 30% of wooden houses”. The data on damage to wooden houses for the nine events show that the area of I=VII extends up to 5km on both sides of the fault in the case of faults through mountainous region. On the other hand, in the case of earthquake faults lying underneath basins, where sediments have accumulated from the Late Pleistocene to Holocene, the area of I=VII extends over a wider area and occasionally fills the whole basin. The ground condition is seen to be an important factor in generating strong ground motion with I=VII. A similar result is obtained from an examination of the 1923 Kanto earthquake near source region with the thrusting fault at a depth shallower than 20km. The Kanto earthquake is one of the typical disastrous inter-plate earthquakes in Japan. The data on the directions of simple bodies that have overturned and collapsed wooden houses in the proximity of earthquake faults indicate that systematically larger ground motions occur in a direction normal to the strike than parallel to it irrespective of the type of faulting. The effective periods for these simple bodies and wooden houses are estimated to be in the range of 0.3sec to 1.5sec. These results indicate that the dominant strong ground motion in the direction normal to the strike plays an important role in generating the severe damages in regions hit by intensity I=VII.
著者
広瀬 一聖 川崎 一朗 岡田 義光 鷺谷 威 田村 良明
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.53, no.1, pp.11-23, 2000-07-25 (Released:2010-03-11)
参考文献数
23
被引用文献数
1 3

科学技術庁防災科学技術研究所の関東・東海地域の地殻変動連続観測記録を, BAYTAP-G [ISHIGURO and TAMURA (1985)] を用いて解析し, 1989年12月9日, 南関東一帯で, 時定数約1日の傾斜ステップが生じたことを見いだした.データの観測数が少ないので, インバージョンにおける自由度を減らすため, 傾斜ステップの震源はフィリピン海プレートの上面の非地震性スベリと仮定し, ISHIDA (1992)によるフィリピン海プレートの上面にそって0.1度ごとに, 断層の走向, 断層の傾斜, スリップの方向, 食い違いの大きさの4つのパラメーターをフリーに, 断層面モデルを求あるインバージョンを行った.その結果, 次のことがわかった. 断層面の主要部分がFig. 7のように東京湾に分布し, ほぼ北に向かって約13度で低角に傾く, 下盤のスリップ・ベクトルの方向北60度西の, フィリピン海プレートの沈み込みと大局的に調和的な断層面モデルが得られた. 解放されたモーメントは約0.7×1018Nm (Mw5.9相当) であった. ただし, 統計的検定からは, 東京湾中央部ではなく東京湾周辺である可能性も存在する.震源核 (サイレント・アースクェイク) の発生予測を行うには, その発生法則が重要である. しかし, 日本列島周辺のスロー・アースクェイクやサイレント・アースクェイクの発見事例は数個しかないので, 発生法則などを議論するには時期尚早である. スロー・アースクェイクやサイレント・アースクェイクなど間欠的非地震性すべりの経験を蓄積することが, 地震短期予知研究の戦略として重要であろう.1989年12月の事例ではS/Nの良い記録が少なく, フィリピン海プレート上端という条件を付けざるをえなかったとか, インバージョンによって得られた断層の位置の分解能など, 残された問題もあるが, 本研究で得られた知見は, 発展し始めたばかりの「非地震性すべりを組み込んだプレート境界ダイナミクス研究」や, 地震予知研究などの関連諸分野の研究にとって, 意義ある一ステップとなるであろう.
著者
松浦 律子
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.1, pp.1-7, 2012-09-28 (Released:2012-10-26)
参考文献数
17
被引用文献数
6

There are several European historical materials on Tensho Earthquake, which occurred on Jan. 18, 1586 in the south-western part of Chubu district. The through research of those materials revealed that all the information of Tensho earthquake was originated from letters written by L. Frois in October 1586 at Shimonoseki Port, Yamaguchi Prefecture as the annual report of missionary in Japan. Since a letter was hand-copied, edited, and translated to Italian or Latin from Portuguese in the late 16th century, there derived some versions of descriptions on damage of the earthquake. The letter in the Portuguese version published in Evora, Portugal in 1589, and the remained copies of the manuscript of "Japanese History" by Frois are only two reliable sources. From those credible European materials, it is apparent that there was the common talk in Kyoto after Tensho earthquake of Tsunami damage along the northwestern coast of Japan. However, it is no more than a rumor.
著者
瀬野 徹三
出版者
SEISMOLOGICAL SOCIETY OF JAPAN
雑誌
地震 第2輯 (ISSN:00371114)
巻号頁・発行日
vol.64, no.2, pp.97-116, 2012-01-25 (Released:2012-02-20)
参考文献数
83
被引用文献数
7 9

Great earthquakes have historically occurred along the Nankai Trough. It has been said that they ruptured part or whole of characteristic fault planes A, B, C, D, and E repeatedly. However, there are a number of enigmas for their occurrence. Major ones are as follows. The 1944 Showa-Tonankai earthquake occurred only 90 years after the 1854 Ansei earthquakes. The 90-year period seems short compared with other time intervals of the historical earthquakes. The Tonankai earthquake did not rupture fault plane E west of the Suruga Trough, by some unknown reasons. The Tokai earthquake anticipated at fault plane E has not occurred yet since the Ansei-Tokai event even if a slow slip event occurred recently near the downdip end of its rupture zone. In this study, I propose a model to solve these enigmas. I characterize a fault plane of a great earthquake into a seismic-b.eq, a tsunami-b.eq, and a geodetic-b.eq, in which seismic waves, tsunamis, and crustal deformations are dominantly generated, respectively. I compare these different bands of rupture zones between the 1944 Showa-Tonankai and 1854 Ansei-Tokai earthquakes, the 1946 Showa-Nankai and 1854 Ansei-Nankai earthquakes, and the 1707 Hoei and other earthquakes, using seismic intensity data and previous studies on asperities, tsunamis, and crustal deformations. It is found that the Ansei-Tokai and Showa-Tonankai earthquakes scarcely shared their seismic-b.eqs. The tsunami- and geodetic-b.eqs of the Ansei-Tokai earthquake extended to the west of its seismic-b.eq, and was shared by, but did not cover the seismic-, tsunami- and geodetic-b.eqs of the Showa-Tonankai earthquake. It cannot thus be said that the Ansei-Tokai earthquake ruptured fault planes C+D+E or that fault plane E was left unbroken after the Showa-Tonankai earthquake. The occurrence of these two earthquakes is rather complementary from a viewpoint of the seismic-b.eq. The seismic-b.eq of the Ansei-Nankai earthquake also seems to have been different from and was located further north than that of the Showa-Nankai earthquake. On the other hand, the Hoei earthquake had a seismic-b.eq similar to those of the Showa earthquakes. I group historical great earthquakes into the Ansei-type or the Hoei-type, which has a seismic-b.eq similar to either of the Ansei or Hoei earthquake. It is likely that the Ansei-type earthquakes are the 684 Hakuho, 1096 Eicho-1099 Kowa, 1498 Meio, and 1854 Ansei earthquakes and recurred with a ∼400-year period, and that the Hoei-type earthquakes are the 887 Ninna, 1361 Shohei, 1707 Hoei, and 1944 Tonankai-1946 Nankai earthquakes and recurred with a ∼350-year period. Since the Showa-Tonankai earthquake was complementary to the Ansei-Tokai earthquake, the 90-year period between the two events is not a recurrence time and it is natural that the Showa-Tonankai did not rupture fault plane E. It is also natural that the next Tokai earthquake did not occur even if the slow slip event occurred at its downdip end, because it is expected to occur at least ∼200 years after present, because the earthquake precedent the Ansei-Tokai event would be the 1498 Meio earthquake.
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 第2輯 (ISSN:00371114)
巻号頁・発行日
vol.29, no.4, pp.355-363, 1976-12-15 (Released:2010-03-11)
参考文献数
5
被引用文献数
2 2

The Kalapana tsunami was generated off the south coast of Hawaii Island, accompanying the earthquake of magnitude Ms=7.2 (NOAA), at 14h 48m (GMT), Nov. 29, 1975. Some features of this tsunami are investigated on the basis of tide gauge records of NOAA and Japan, adding the reports of the US field investigation.Tsunami magnitude of the Imamura-Iida scale is decided as m=2, judging from the tsunami heights observed near and distant fields. The initial motion of the tsunami waves was in an upward direction at the whole Hawaiian stations, suggesting the uplift of the sea-bottom in the tsunami source area. The source dimension of tsunami is inferred to be 70km along the south coast of Hawaii Island, and the area is 2.2×103km2. By applying the corrections for the refraction and shoaling from the inundation heights at the Hawaii Island, the average vertical displacement of 1.2m would be occurred in the source area. The tsunami energy of approximately is 1.6×1020 ergs. According to statistical relation, the present tsunami is large compared with the earthquake magnitude.The tsunami fronts arrived in NE Japan at about 7h 40m after the occurrence of the earthquake. The maximum double amplitude is 20-30cm with the period of about 15min and the amplitude is relatively higher than that in SW Japan. It is noticed that the wave rays emitting the tsunami source concentrate in the Kuril Islands.
著者
宇津 徳治 関 彰
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.7, no.4, pp.233-240, 1955-03-30 (Released:2010-03-11)
参考文献数
28
被引用文献数
6 11

The after-shock regions of 39 shallow earthquakes which took place in and near Japan (Table 1) are determined and the relation between thier areas and the magnitudes or energies of main-shocks is investigated. If we assume that the logarithm of the area A (km2) and the magnitude M are in linear relation, i. e., logA=aM+b (Fig. 2-3), the constants a and b become as follows, a=1.02±0.08, b=-4.01±0.57 (for 39 total earthquakes)a=0.93±0.08, b=-3.18±0.61 (for 23 oceanic earthuakes)a=0.85±0.10, b=-3.05±0.72. (for 16 land earthquakes)From the relation between M and E (erg), we get A∝Em, where m≈1/2, then E/A∝A∝√E, this means that the surface density of energy increases as the energy increases.