著者

松本 剛 木村 政昭

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.45, no.4, pp.417-426, 1993-03-24 (Released:2010-03-11)

参考文献数

20

被引用文献数

5

---

Historical record shows that a large-scale tsunami named “the Great Meiwa Tsunami” or “the Yaeyama Earthquake Tsunami” occurred on 24th April 1771 in the sea region of Miyako and Yaeyama Islands, westernmost part of Ryukyu District caused by a large earthquake and the tsunami inundated up to the inside of the islands. Swath bathymetric survey in this area was conducted by the use of SEABEAM and HS-10 systems on board the Research Vessels KAIYO and YOKOSUKA, in November 1990, April 1991, January and April 1992. Precise topographic contour map was completed in the area of 22°40′N-24°10′N, 122°50′E-126°20′E, including the westernmost part of the Ryukyu Trench and tsunami source area (around 24.0°N, 124.3°E). The survey area is classified into five different topographic domains which are arranged zonally. Those are:Zone 1: north of 24°00′N, which is characterised by the distribution of well developed submarine canyons along the southern coasts of Yaeyama Islands.Zone 2: 23°40′N-24°00′N, which is characterised by deep sea fans and its large-scale subsidence edged by steep scarp near 23°55′N-24°00′N, 124°10′E-124°20′E. The observed relative height of the depression is about 200-300m.Zone 3: south of 23°40′N on the landward slope of the trench, which is characterised by quite complicated topography such as several escarpments and ridges and troughs of which trend is not clearly recognized.Zone 4: trench axis area with depth about 6500-6600m, which is characterised by broad plain. Maximum width of the axial plain is about 40km.Zone 5: seaward slope of the trench, which is characterised by horsts and grabens which are samely distributed in the sea area of the south of Okinawa Island. The strike direction of the horsts and grabens is NW-SE off Miyako Islands, and WNW-ESE off Yaeyama Islands.The 1771 Meiwa Tsunami is considered to be originated by the large-scale subsidence of the deep sea fans which is composed of soft sediment derived from the submarine canyons just north of the fans, and the wave might be propagated along the canyons from the position of the tsunami source.Tention of N-S direction is suggested by the topographic features in the survey area, and the tention stress in this area is considered to be the origin of the large-scale subsidence which induced the tsunami.

著者

高橋 浩晃 笠原 稔

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.2, pp.115-130, 2004-12-27 (Released:2010-03-11)

参考文献数

62

被引用文献数

2

---

The Tokachi-oki earthquake (MJMA8.0) occurred on September 26, 2003 (JST) off southeastern Hokkaido, Japan. We investigate the seismic activity before and after the mainshock using hypocenter catalogues produced by Japan Meteorological Agency and Hokkaido University. A decline of seismic activity and a seismic gap in the asperity of the 2003 earthquake had been clearly recognized from the early 1990's to just the mainshock faulting. Similar low seismicity had been observed before the former 1952 Tokachi-oki earthquake (MJMA 8.2). These facts may reflect that the plate boundary fixed loosely has become tight coupling during one seismic cycle. A relatively low seismicity patch during the interseismic phase corresponds to the asperity. This suggests that interseismic seismic activity is strongly controlled by existence of the asperity. The aftershock region of the 2003 earthquake is approximately 160km by 160km, which is slightly smaller than that of the 1952 earthquake. This feature is in good agreement with the slip distributions of the 1952 and 2003 earthquakes estimated from tsumani waveform inversions. Large aftershocks are located out of the asperity, which may reflect the stress status in and around the asperity. Remarkable triggered seismic activity has begun just after the mainshock along the volcanic front in the eastern Hokkaido.

著者

奥村 晃史 下川 浩一 山崎 晴雄 佃 栄吉

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.425-438, 1994-03-14 (Released:2010-03-11)

参考文献数

25

被引用文献数

9 19

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The middle section of the Itoigawa-Shizuoka Tectonic Line (Middle ISTL) is an active fault system that extends NW-SE for 50km from Matsumoto to Kobuchizawa, in central Japan. The Middle ISTL is characterized by high average slip-rate reaching 8 to 10mm/yr during the Late Pleistocene and Holocene. This is one of the highest slip-rate reported from active faults on land in Japan. Empirical relation between slip-rate and recurrence time indicates that the Middle ISTL may rupture more than once a thousand year. The previously known recurrence time estimates of 3500 to 5000 years were significantly longer than the expected recurrence time. The last faulting event on the Middle ISTL most likely occurred in 841 A. D. according to historic record and paleoseismological works. Since the elapsed time is about 1152 years, the estimation of recurrence time is critical to evaluate the potential of next earthquake. In order to know the history of recent faulting events, we excavated the Gofukuji fault, the northernmost segment of the Middle ISTL at Namiyanagi, south of Matsumoto. Investigation of 6 trenches, 3 test pits and topography around the trenches brought following results. The ages of three most recent faulting events are 445-1386 A. D., 150-334 A. D., and 839-189 B. C. The recurrence time is between 111 and 1236 years. Assuming the correlation of the last event with the 841 A. D. event, the recurrence time is estimated to be 338 to 1172 years. Average recurrence interval in this case ranges 515 to 840 years. The elapsed time of 607 to 1152 years is probably longer than the recurrence time. The average slip rate of the fault since c. a. 6000 B. C. is 9.4±4.5mm/yr left-lateral. The left-lateral coseismic slip during the last event is estimated as 7.5±1.5m.

著者

佐藤 春夫

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.85-97, 1991-07-24 (Released:2010-03-11)

参考文献数

94

被引用文献数

3

---

Seismic waves are refracted, diffracted and/or reflected by random inhomogeneities which exixt in the real earth medium. Coherent phases have been well studied especially for the structure study of the lithosphere, where discrete impedance contrasts are supposed. Array obsevations made it possible to measure the precise velocity structure by tomography. Complementary to such a deterministic approach, the random inhomogeneous structure of the earth medium has been statistically studied, where a focus is put on the systematic change in amplitudes of incoherent phases of seismic waves. A latter part of S coda first attracted seismologists to its systematic decay in amplitudes, which offered the way to evaluate quantitatively the short wavelength components of randomness since coda waves are excited due to their large angle scattering. Several models have been proposed to simulate the excitation of coda waves: a single scattering model; a diffusion model; and an energy flux model. The scattering coefficient g which characterizes the coda excitation and coda Q-1 which characterizes the decay in coda amplitude have been often measured in various areas in the world as tectonic parameters. The energy conservation law suggests that the excitation of coda waves mean the reduction in amplitude of direct waves: the seismic energy of direct waves flows into a coda portion with the increase in propagation distance. Scattering due to random structure has been considered as a dominant mechanism of attenuation. Frequency dependence of attenuation and coda excitation has been studied in relation with the spectral structure of randomness. Recent observations report that Qs-1 decreases with frequency for frequency higher than 1Hz. A theoretical model predicts that Qs-1 is proportional to the reciprocal of frequency when the randomness is characterized by the exponential autocorrelation function. The separation of intrinsic loss and scattering loss from total attenuation is one of the most important subject. Seismic waves which are pulse-like in time when radiated from the hypocenter collapse with travel distance. Such a characteristic has been studied in relation with the diffraction and multiple forward scattering due to long wavelength components of velocity inhomogeneities. The parabolic approximation well explains the broadening of seismogram envelope and the delay in the maximum amplitude arrival from the onset of direct wave. We have to examine seismograms of not only a short time window around the direct wave but a long time window starting from the direct wave to the end of coda. That is, it is very necessary to make more sophisticated models for full seismogram envelopes adopting the difference in randomness related to seismo-tectonics.

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.28, no.4, pp.461-471, 1975-12-10 (Released:2010-03-11)

参考文献数

14

被引用文献数

6

---

Adding mareographic data at the Kuril Islands, the source areas of the 1973 Nemuro-oki tsunami and the 2nd tsunami accompanying the largest aftershock on June 24, 1973 are reanalyzed. The result is the same as shown in the preliminary report: The source length of the 1973 Nemuro-oki tsunami is 130km long parallel to Nemuro Peninsula and the area is 7.2×103km2. The source length of the 2nd tsunami is 100km which is longer than the aftershock area reported by NOAA, and the western half of the source area seems to overlap with the source area of the first tsunami.The 3rd tsunami of Sept. 27, 1974 was observed with small amplitude at Hanasaki. The estimated source area of this tsunami is within the source area of the 1973 tsunami. The 4th tsunami of June 10, 1975 was generated by an earthquake with the magnitude of about 7 (JMA), but the tsunami magnitude was relatively large. According to the author's method based on the attenuation of tsunami height with distance, the tsunami magnitude (Imamura-Iida scale) is m=1.5. This magnitude is the same grade to that of the 1973 Nemuro-oki tsunami. The estimated source area falls inside the source area of the 1969 Shikotan tsunami. The source length is about 100km long and its area is 6.3×103km2. The sea-bottom of this area may be uplifted, judging from the initial motion of the tsunami observed at Hokkaido and Sanriku.The source areas of the tsunamis generated after the 1973 Nemuro-oki tsunami moved to the north-eastern direction along the continental slope. Within the source area of the 1969 Shikotan tsunami, many tsunami sources are located. On the contrary, there is a remarkable gap of the tsunami source area between the 1952 Tokachi-oki and the 1973 Nemuro-oki tsunamis. The source area of the 1973 tsunami occupies only the eastern half of the 1894 tsunami source. The area to the south-west of the 1973 tsunami may be considered a region of relatively high tsunami risk.

著者

髙橋 利昌 浅野 彰洋 大内 泰志 川崎 真治 武村 雅之 神田 克久 宇佐美 龍夫

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.60, no.3, pp.193-217, 2008-02-15 (Released:2013-08-20)

参考文献数

40

被引用文献数

1 1

---

The major earthquakes of M=7 class, so-called Geiyo earthquake, have occurred in the subducted slab of the Philippine Sea plate under Aki-nada and Iyo-nada sea. The upper surface of the Philippine Sea plate is located in the depth from 40-45km in this region. Five Geiyo earthquakes can be found in 1649, 1686, 1857, 1905, and 2001 since 17th century. Magnitudes M of the older 4 events were larger than 7, while that of the last one is 6.7 in JMA (Japan Meteorological Agency) scale. Magnitudes and locations of focal regions of them were redetermined from seismic intensity data by the method of an attenuation curve fitting and of the seismic intensity inversion. Optimal magnitudes of old events were obtained between 6.7 to 6.9. This results show the old 4 events have almost the same magnitude as the 2001 event. One of the possible reasons why the former values were overestimated is that the empirical relation between magnitude and isoseismal area from inland shallow earthquakes was applied to determine the magnitude of the historical intraslab events such as Geiyo earthquakes.

著者

平原 和朗

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.2, pp.291-306, 1990-06-24 (Released:2010-03-11)

参考文献数

107

被引用文献数

1

---

Seismic tomography has revelaed the three-dimensional structure of Earth's interior in several scales, which has improved our understanding of geophysical and geological processes in the Earth. The present paper reviews three-dimensional inversion methods of seismic body-wave data, stressing the technical details encountered in actual analyses of travel time data. Especially, the paper gives the detailed description of the formulation of three-dimensional inversion problems, the parameterization of structure, the technique of parameter separation, and solving methods of observational equations with resolution analyses (a matrix and interative back-projection methods).

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.47, no.2, pp.183-183, 1994-08-14 (Released:2010-03-11)

参考文献数

2

著者

岩田 孝仁 浜田 信生

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.39, no.4, pp.621-634, 1986-12-25 (Released:2010-03-11)

参考文献数

18

被引用文献数

1 1

---

In the present study, we have accumulated most complete seismological data and reinvestigated the seismicity associated with the 1944 Tonankai earthquake. Because of poor observation and social difficulty during the World War II, incompleteness and insufficiency in observational data resulted in rather obscure view about the actual process and mechanism of the earthquake. Number of aftershocks and their location accuracy reported by existing studies seem to be dissatisfactory for detailed discussion.We found some observational data that are still available but have not been used yet, then, we applied a modern hypocenter location method to the newly compiled data and succeeded in increasing the number of accurately located aftershocks more than twice. The followings are important findings of the study.The mainshock initiated from the bottom of the fault plane, in the south-west corner of the focal region. This feature is in accordance with the results of some previous studies. Most of aftershocks concentrated in the vicinity of the Shima spur, which extends south-east from the Shima peninsula to the Nankai trough. Temporal broadening of the aftershock region toward south-east along the spur is recognized and this trend seems to continue over 40 years until now. Distribution of aftershocks around Shionomisaki, the southern top of the Kii peninsula, may suggest some overlapping of the focal regions of the Tonankai and the 1946 Nankaido earthquake. Aftershock activity or induced seismicity is also recognized in the middle part of Shizuoka prefecture where some seismologists assume the focal region of a future interplate earthquake, so called Tokai earthquake. Seismicity around the southern Izu peninsula may represent an induced activity along one of the active faults which strikes southeast from the peninsula. Other induced seismic activity in inland area of central Honshu indicates a large extent of the effect of the interplate earthquake on the tectonic environment of the mentioned area. This study will contribute to gain better understanding of the process and mechanism of the Tonankai earthquake.

著者

神田 茂

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.15, no.2, pp.143-145, 1962-06-30 (Released:2010-03-11)

著者

今村 明恒

出版者

公益社団法人 日本地震学会

雑誌

地震 第1輯 (ISSN:00371114)

巻号頁・発行日

vol.16, no.5, pp.103-104, 1944-05-18 (Released:2010-11-17)

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.26, no.2, pp.204-205, 1973-10-30 (Released:2010-03-11)

参考文献数

8

被引用文献数

1

著者

佐竹 健治

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.44, no.Supplement, pp.99-112, 1991-07-24 (Released:2010-03-11)

参考文献数

82

被引用文献数

1

---

Recent studies on tsunamis are reviewed. Theoretical studies on tsunami generation and propagation have been done both on coupled and decoupled systems of ocean and solid earth. Both approaches are proved to be equivalent. Hydrodynamic formulation, on the basis of decoupling model, is discussed in detail. Several models have been proposed for the mechanism of tsunami earthquakes that produce abnormally large tsunamis compared to seismic waves. After the 1983 Japan Sea tsunami, some progress has been made on tsunami research. Among them are re-examination of tide-gauge system, studies on free oscillation of the Japan Sea and newly developed inversion technique of tsunami waveforms to estimate complex fault motion. Large-scale realistic computation of tsunamis can be made very rapidly and has potential usage for tsunami warning system. These seismology-related problems are described.

著者

飯尾 能久 松本 聡 松島 健 植平 賢司 片尾 浩 大見 士朗 澁谷 拓郎 竹内 文朗 西上 欽也 廣瀬 一聖 加納 靖之 儘田 豊 宮澤 理稔 辰己 賢一 和田 博夫 河野 裕希 是永 将宏 上野 友岳 行竹 洋平 Bogdan ENESCU

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.463-475, 2006-03-31 (Released:2010-03-11)

参考文献数

44

被引用文献数

1 2

---

The 2004 Mid Niigata Prefecture Earthquake (MJMA 6.8) occurred on 23 October 2004. The mainshock was followed by four aftershocks with MJMA≥6.0. This earthquake is located in the Niigata-Kobe Tectonic Zone in which large strain rates (>0.1ppm/y contraction) have been observed by GPS data. We deployed three temporary online seismic stations in the aftershock area. Combining data from the temporary stations and from permanent stations around the aftershock area, we determined aftershock locations, and estimated the structures and the stress change in and around the aftershock region. Based on these results, we suggested a generating process of the 2004 Mid Niigata Prefecture Earthquake supposing that a very weak region exists in the weak zone in the lower crust just beneath the seismogenic fault.

著者

加藤 祐三

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.40, no.3, pp.377-381, 1987-09-25 (Released:2010-03-11)

参考文献数

6

被引用文献数

2

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In Ishigaki Island, the southern Ryukyu Islands, there are many blocks consist of coral limestone. These are considered to be thrown onto the island by Yaeyama Seismic Tsunami in 1771 and so called “tsunami-ishi (means tsunami-stone)”. Based on a distribution of these tsunami-ishi, a record, in archives, saying that the run-up height of the tsunami was 85 meters has been admitted. Or according to the maximum height of the distribution, an assertion that the run-up height is 55 meters has been made.There are two kinds of blocks for these tsunami-ishi. One is genuine tsunami-ishi which is evidently thrown on the island by the tsunami. The other consists of the Pleistocene Ryukyu Limestone block. It cannot be determined whether the existence of these blocks is a result of the tsunami, or not. These coral blocks can be distinguished from each other by its components, either aragonite or calcite. That is to say, when the coral of a block consists of aragonite, it should be a genuine tsunami-ishi. When calcite, it should be a Ryukyu Limestone block. Since the research, made by this method, found out that the maximum height of the distribution of the genuine tsunami-ishi was 25 meters, it is inferred that the run-up height was a little higher than 25 meters.In Miyara Bay of Ishigaki, there is also a block about 100 tons in weight clung by some small coral whose 14C-age corresponds with that of Yaeyama Seismic Tsunami. The 14C-age of this block itself is 2980BP. This suggests that, between at least 3000 years ago and 1771 of Yaeyama Seismic Tsunami, there was no such huge tsunami which could have thrown this large block at Miyara coast. Since, among the genuine tsunami-ishi, the 14C-age of coral of a block, distributing at the altitude of 25 meters, which is the highest altitude for this particular block, is 1810BP, this block is inferred to have been thrown by the tsunami and the value of a little higher than 25 meters is considered to indicate the maximum height of Yaeyama Seismic Tsunami.

著者

吉田 真吾 加藤 尚之

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.58, no.3, pp.231-246, 2005-12-25 (Released:2010-03-11)

参考文献数

44

被引用文献数

1

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This paper reviews studies on the relation between the eventual earthquake size and its rupture nucleation size. Although a large number of studies have been made in order to find whether the seismic nucleation phase depends on the eventual earthquake size or not, this subject is still in controversy. Several recent papers have reported that the duration of the seismic nucleation phase scales with the final rupture size, and that the scaling relation can be explained by rupture nucleation models. These studies suggest that larger preslip occurs before a larger earthquake. On the contrary, other papers have reported that the seismic nucleation phase is independent of the earthquake size; earthquakes of all sizes initiate in a similar manner. Adding to these existing studies, we perform a numerical simulation of sliding behavior on a fault assuming two asperities of different sizes. The result shows that when the rupture of the small asperity triggers the rupture of the large asperity, short term preslip occurs at the small asperity, and the magnitude of the preslip does not depend on the eventual earthquake size. However, intermediate-term aseismic slip which occurs around the main asperity depends on the eventual earthquake size.

著者

〓刀 卓 青井 真 中村 洋光 藤原 広行 森川 信之

出版者

日本地震学会

雑誌

地震. 2輯 (ISSN:00371114)

巻号頁・発行日

vol.60, no.4, pp.243-252, 2008-03-31

被引用文献数

5

著者

今村 明恒

出版者

公益社団法人 日本地震学会

雑誌

地震 第1輯 (ISSN:00371114)

巻号頁・発行日

vol.12, no.5, pp.220-222, 1940-05-25 (Released:2010-11-17)

著者

一窓庵

出版者

公益社団法人 日本地震学会

雑誌

地震 第1輯 (ISSN:00371114)

巻号頁・発行日

vol.7, no.9, pp.496-497, 1935-09-15 (Released:2010-03-09)

著者

久保寺 章 岡野 健之助

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.13, no.4, pp.210-218, 1960-12-25 (Released:2010-03-11)

参考文献数

5

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The seismic waves due to the great nuclear explosions in the central Pacific Ocean (Bikini Atoll) in June and July 1958 were recorded by routine seismographs at the Abuyama Seismological Observatory of Kyoto University.The remarkable result was that we found a new kind of wave-group which has the following properties on the records of long-period seismograph. The wave in this group is of a period 9 to 1 minute and its propagation velocity is about 300m/s. The arrival time is about 3 hours later than that of seismic P-wave. These properties are similar to those of the microbarographic oscillations produced by the nuclear explosions, and the phenomena can hence be attributed to the effect of atmospheric pressure fluctuations upon the inertia mass of the seismograph.