著者

鈴木 康弘 池田 安隆 渡辺 満久 須貝 俊彦 米倉 伸之

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.42, no.2, pp.151-159, 1989-06-24 (Released:2010-03-11)

参考文献数

17

被引用文献数

5 2

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Many active faults trending N-S along basin-mountain boundaries are recognized in Northeast Japan, but only a few of them have experienced surface faulting in historical time; most of them seem to have been quiescent in the past several hundred years or more. Thus earthquakes are anticipated to occur from these active faults in the near future. To detect the recurrence intervals of faulting, which can be obtained by the excavation study, is indispensable for the long term prediction of earthquakes.We excavated a trench at Kitasakai, Sakata City, across the Kannonji fault, one of the eastern boundary faults of the Shonai plain, Northeast Japan, in order to reveal its late Holocene activity including a possible faulting event associated with the Shonai earthquake (M=7.0) of 1894 A. D., which caused severe damage along this fault.Our excavation has revealed that (1) the last surface faulting event on the Kannonji fault occurred in a period from 2, 500 years B. P. to 1894 A. D., and that (2) no surface faulting occurred (at least at the trenching site) in association with the Shonai earthquake of 1894. Careful examination of historical records, however, strongly suggests that the earthquake of 1894 was also generated from this fault; it is likely that thick, unconsolidated sediments prevented the rupture from propagating up-dip to the surface. These results indicate that the interval between the last two earthquakes originating from the Kannonji fault is less than 2, 500 years. It could be 1, 000 years, because the event revealed by excavation is possibly correlated to the historically-documented earthquake of 850 A. D..

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.38, no.1, pp.1-12, 1985-03-25 (Released:2010-03-11)

参考文献数

15

被引用文献数

2 18

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The N-S extensional strain field in the Kyushu is understood as the result of the crustal deformation caused by the rifting and the spreading of the Okinawa Trough which crosses the Central Kyushu in the E-W direction. The spreading velocity and the spreading direction of the Okinawa Trough in the Kyushu have been estimated as 1.4cm/a and N-S direction, respectively, by the analysis of the distance survey. The horizontal and the vertical crustal movements, the normal active faults, the gravity anomaly, the volcanism, and the fault plane solutions of the earthquakes in the Shimabara Peninsula suggest that the Unzen Volcanic Graben is an active rift of the Okinawa Trough. The beginning of the spreading of the Okinawa Trough in the Kyushu has been estimated to be during the period from 0.8Ma to 0.5Ma B. P. by the spreading velocity and the width of the Unzen rift. The distributions of the active faults, the low gravity anomaly belts, the hypocenters of the shallow earthquakes and their fault plane solutions suggest that Okinawa Trough in the Kyushu consists of the three rifts whose strikes are E-W direction and the three transform faults like shear fault zones whose strikes are the NE-SW direction.

著者

宮川 康平 中西 一郎 三浦 勝美 田中 聡

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.51, no.1, pp.113-121, 1998-07-03 (Released:2010-03-11)

参考文献数

18

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The Geiyo earthquake occurred on June 2 in 1905 in the western Seto Inland Sea between the Honshu and Shikoku Islands, Japan. The seismograms of the earthquake obtained at the stations of Central Meteorological Observatory were newly found at Earthquake Research Institute of the University of Tokyo. They are recorded by the Omori seismometers and tromometers, which are superior to former seismometers with respect to continuous recording. For the estimation of the magnitude and source mechanism from the seismograms, we digitize 3 records, which are Hongo EW component, Hitotsubashi EW component and Tokyo tromometer. We have to know the response of the Omori seismometer to estimate the ground motion during the earthquake. In order to know the frequency characteristics of the seismometers, we calculate their Fourier amplitude spectra. The spectra of the Hongo EW component and Hitotsubashi EW component show clear peaks which may be considered as the natural periods of the seismometers. The natural periods of Hongo EW component and Hitotsubashi EW component are about 60s and 25s, respectively. The damping constant estimated from the free oscillation record of Omori seismometer at Ishinomaki observatory is less than 0.01, and the friction is 1.7mm.

著者

竹内 均 金森 博雄

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.21, no.4, pp.317-317, 1969-02-25 (Released:2010-03-11)

被引用文献数

1

著者

瀬野 徹三

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.29, no.2, pp.197-200, 1976-05-15 (Released:2010-03-11)

参考文献数

9

著者

瀬野 徹三

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.30, no.3, pp.253-264, 1977-12-05 (Released:2010-03-11)

参考文献数

18

被引用文献数

1

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In the previous paper (SENO, 1977), the method of calculation of the recurrence time interval of great earthquakes in the Nankai and the Sagami trough regions was improved and refined. The recurrence time interval T and the value d (so-called recovery ratio) were estimated at the several sites on the seismic crustal movement areas along these troughs.In the present paper, the vertical crustal movement observed by precise levellings and the defomation of the Holocene terraces in the south Kanto district are reexamined because the deformation of the coastal terraces have some complicated relations with the seismic crustal deformations in this region.In the Shonan district, the deformation of the Holocene terraces is attributed to the crustal deformation associated with the 1923 Taisho type earthquakes and the recurrence time T of 180-400 years and the value d of 0.25-0.50 are obtained. In the southern Boso peninsula, the deformation of the Holocene terraces is divided into two: the crustal deformation associated with 1923 type earthquakes and that caused by the fault off the Boso peninsula which moved at the time of the 1703 Genroku earthquake. The recurrence time T and the value d for this fault off the Boso peninsula are estimated to be 950-2500 years and 0.20-0.54, respectively.

著者

松浦 充宏

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.53-62, 1991-07-24 (Released:2010-03-11)

参考文献数

36

被引用文献数

4

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Geophysical models are generally estimated from observed data by using some criterion. In most cases observed data are inaccurate, insufficient and inconsistent. To deal with such data we must introduce a new criterion in place of the classical least-squares criterion. The history of the development of inversion theory in geophysics is the history of quest for the new criterion. From such a standpoint we review the development of inversion theory in the last score.In a series of papers published in 1967, 1968 and 1970, G. Backus and F. Gilbert introduced the concept of model resolution and formulated the geophysical inverse problem as the problem of compromising reciprocal requirements for model resolution and estimation errors in some natural way. This was the starting point of the fruitful development of inversion theory in geophysics. Various criteria to compromise model resolution and estimation errors have been proposed in the early part of the 1970s, but the objectivity of these criteria were not clear. At the end of the 1970s D. D. Jackson introduced the concept of prior information about unknown model parameters and combine two reciprocal criteria for model resolution and estimation erros in a natural way. Jackson's approach for linear inversion, which is based on the minimum variance criterion, has been soon exteded to nonlinear cases by A. Tarantola and B. Valette and also by D. D. Jackson and M. Matsu'ura on the basis of probability theory. The geophysical data inversion is now understood as the process of extracting new information from observed data, combining it with prior information about model parameters, and constructing the more clear image of a physical model.

著者

三雲 健 大塚 道男 尾池 和夫

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.23, no.3, pp.213-225, 1970-09-28 (Released:2010-03-11)

参考文献数

17

被引用文献数

1

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The focal mechanism of 20 microearthquakes in the Wakayama region have been determined from the seismograms recorded at ten temporary stations and eight routine network stations covering the region.The hypocenters of the earthquakes have been determined for five different crustal models (with a continuously varied velocity profile), to estimate the accuracy of their location and the emergent angle of seismic rays at the focus. The radiation pattern of P wave first motions for the 15 shocks, which was corrected for an appropriate crustal structure, can be interpreted by the double-couple type mechanism with dipping nodal planes.The average of the maximum pressure axes is oriented nearly horizontally along the N70°W-S70°E direction, while the axes of the maximum tension show a steep dip in many cases. If a slip dislocation is assumed to be a likely model of the earthquakes, the source would be thrust faulting with a predominant component of dip slip. The other five earthquakes shows, however, the radiation pattern inconsistent with the double-couple type mechanism.

著者

石川 有三 尾池 和夫

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.35, no.2, pp.171-181, 1982-06-25 (Released:2010-03-11)

参考文献数

31

被引用文献数

3

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Ten reservoir induced earthquakes were investigated. The relation between the dam height and the maximum magnitude of the induced earthquake was found. We show that there are the magnitude limit of earthquake related with the dam height. The Shenwo earthquake, this was only one exception of this relation, wasn't far from the 1975 Haicheng earthquake. It occurred only 43 days before the Haicheng earthquake. We think the Shenwo earthquake occurred in the precursory period of the Haicheng earthquake. So we concluded that it occurred under the special tectonic condition just before the large earthquake.Fault plane solutions for reservoir induced earthquakes were also compared with those for natural ones. We got the result that the directions of P-axis and T-axis for induced earthquakes were not always same to those for natural ones. So, we concluded that induced earthquakes occurred in the faults which were weakened by the permeated water rather than in the faults which were easily dislocated by the tectonic force. Large aftershocks of the Xinfengjiang earthquake were investigated and we showed the examples of the shock induced by loading and unloading.The b-values for the aftershocks of induced earthquakes were calculated, but we got only one b-value for natural one which could be compared to induced one and there was no significant difference between them.

著者

山田 功夫 深尾 良夫 石原 靖 青木 治三

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.42, no.1, pp.21-31, 1989-03-25 (Released:2010-03-11)

参考文献数

9

被引用文献数

3

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Since late 1986, we have been operating a three-component set of STS seismometers (STS-1) at Inuyama Observatory, Nagoya University, Japan. This is a preliminary report of the two years observation. The STS-1 seismometer equips with three component BRB (BRoadband Band) outputs and three component LP (Long Period) outputs. The lowpass filtered LP outputs are digitized and recorded continuously at a sampling interval of 10s in a dynamic range of about 120dB. These continuous data have been used so far to determine seismic moment or centroid moment tensor of large Japanese earthquakes. The BRB output is recorded on an event recordering system, where the BRB and LP outputs after an eight-pole analog anti-aliased filtering are digitized and recorded for 50 minutes at sampling intervals of 0.1 and 0.4s, respectively. The dynamic range of this system is limited at present by the A/D converter to about 90dB. The triggered BRB data have been used so far to determine the source time functions of large Japanese earthquakes, which suggest the occurrence of backswing of fault motion. To maintain the horizontal component instruments in a stable condition, a care must be taken for variation of atmospheric pressure. The results of the analyses indicate a unique importance of nearby observation of large earthquakes by broadband, wide dynamic range and high precision seismometers such as the STS instruments.

著者

池田 隆司 笠原 敬司 伊藤 健治 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.4, pp.549-557, 1984-12-25 (Released:2010-03-11)

参考文献数

4

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In order to obtain information on the underground structure around the Karasuyama-Sugaonuma fault, we carried out a temporary observation for artificial explosions which were blasted at four sites in Saitama and Ibaraki Prefectures in March 1982. Crossing the southern part of the fault, seven seismometers were deployed on an east-west striking observation line 30km long. For three of the explosions, good records were obtained at all the stations. Travel time analyses provided three layers; apparent p-wave velocities in the layers are 1.7km/sec, 2.8-3.1km/sec and 6.1km/sec from top to bottom. Travel times for the 6.1km/sec layer jump near Sashima-cho, Ibaraki Prefecture, where the western branch of the fault is supposed to lie. For the wave propagating through the topmost layer between the eastern and western sides of the north-south striking fault, a systematic difference in the wave form was observed. Those observed features strongly suggest that not only the basement layer (VP=6.1km/sec) but also upper layers are displaced or fractured by the Karasuyama-Sugaonuma fault.

著者

都司 嘉宣

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.34, no.3, pp.401-411, 1981-10-25 (Released:2010-03-11)

参考文献数

18

---

In the early morning of Dec. 31, 1703 (Genroku 16), an enormous earthquake with magnitude of 8.2 occurred in the south sea region of the Kanto District. It is well known that after the occurrence of the earthquake a huge tsunmi was generated, and that the coasts of the Boso Peninsula, the north coasts of Sagami Bay, and the east coasts of the Izu Peninsula were seriously damaged.Recently several old documents of the Genroku tsunami were also discovered on the coasts of the Tokai district, the Kii peninsula, and the Shikoku Island. In two towns, Nishina and Toi, on the west coast of the Izu Peninsula, inundation height was estimated 3 meters, and the residential areas of these towns were slightly submerged. At Miho village in Shimizu city on the west coast of Suruga Bay, residential areas were intermittently submerged for more than ten days, and the people took refuge in higher places. On the mouth district of the Lake Hamana, seaside banks were eroded, and the mouth of the lake became broader. Thirty-three large junks out of 36 anchored at the open sea of Arai town near the lake, were wrecked. In Ono town on the Chita Peninsula inside the Bay of Ise, a garden of Naiku shrine was washed and eroded, where inundation height was about 2 meters. Tsunami was also noticed at the port of Nagoya. Miwasaki and Taiji towns and Haida village on the south east coast of the Kii peninsula were seriously damaged in spite of the long distance from the tsunami origin. In these places 46 houses were washed away in total and the observed tsunami climbed up to 3 or 5 meters. Tidal irregulaity was also noticed in several ports of Kochi Prefecture on the Shikoku Island.

著者

檜垣 強

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.1, pp.93-100, 1973-06-30 (Released:2010-03-11)

参考文献数

4

---

A pulse-like minute oscillation happened to be recorded simultaneously at the four temporary seismic stations installed 2.5-9.0km apart each other, near Kumamoto city. The oscillation lasted only half a second which appears to be too short against the common understanding of earthquake phenomena. Amplitude is incredibly small as well.However, there are a few evidences to support that it is an “earthquake.” It is followed by an earthquake of moderate size, the observed time intervals between two events being about 18 seconds at every stations. The observed directions of initial P motion are reversed between these two events at every stations suggesting that they are physically connected. The hypocenter of this micro-earthquake can be accurately located by seismic technique.The provisional estimation of its magnitude has shown that it is less than -3.

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

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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

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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

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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

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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

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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

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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).