著者

島崎 邦彦

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.25, no.1, pp.24-32, 1972-07-30 (Released:2010-03-09)

参考文献数

7

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Occurrence of destructive earthquakes in Tokyo area during historical time has been investigated by several authors. Possibility of 69-year as well as 36-year periodicity of earthquake occurrence was proposed on the basis of periodgram analyses. A basis of these hypotheses is Schuster's criterion which is applicable only to any one harmonic term obtained from a random sampling. Although the above periodicities are obtained by applying the criterion to the largest of the harmonic terms, the writer believes that, in order to test the largest, we must adopt Fisher's test.A periodgram of a discrete time series of the earthquake frequency is computed for the Tokyo area. It is shown that the periodicity corresponding to its greatest peak is not statistically significant by Fisher's test at significance level 0.1.

著者

川勝 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.43, no.3, pp.447-450, 1990-09-24 (Released:2010-03-09)

参考文献数

10

被引用文献数

1

著者

長宗 留男

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.33, no.1, pp.71-78, 1980-03-25 (Released:2010-03-11)

参考文献数

7

被引用文献数

1

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The epicentral distribution of aftershocks shows that the source region of the Izu-Oshima-Kinkai Earthquake of January 14, 1978 (origin time: 12h 24m 38.6s, 34°46′N, 139°15′E, depth: 0km), consisted of two areas, i. e., the area in the sea between Izu-Oshima and the Izu-Peninsula, spreading to the west from the epicenter of the main shock, and the one in the Izu-Peninsula, extending to the westnorthwest direction from the east coast of the peninsula.On the other hand, it has been pointed out that the earthquake was a multiple shock, and that the second event took place about 6sec after the occurrence of the main shock (first event). The location of the second event, however, was somewhat undefinitely.The records of the JMA 59-type electromagnetic seismographs were examined for locating the origin of the second event.From the readings of the first arrivals of P-waves, the origin for the second event was estimated as follows:Origin time: 12h 24m 44.5s (5.9sec after the occurrence of the main shock), Location: 34°46′N, 139°00′E (approximately 23km west of the epicenter of thee main shock), Depth: 0km.It appears that the second event occurred at a place linking two source areas mentioned above, when the rupture which started at the origin of the main shock and propagated westwards, deviated its direction of propagation to the westnorthwest.

著者

堀 貞喜

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.2, pp.203-213, 1997-08-28 (Released:2010-03-09)

参考文献数

36

被引用文献数

2

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The upper mantle earthquakes occurring within the Philippine Sea plate subducting beneath the Kanto district, Japan, were investigated for their hypocentral distribution and focal mechanisms. Earthquakes located above the double seismic plane, which is formed in conjunction with the subducting motion of the Pacific plate, were picked up on a graphic display with an “on-map selection” method. Hypocentral parameters were re-determined with removing stations far from the epicenter and with introducing station corrections to the observed arrival time data. Based on the relocated hypocenters, the focal mechanism solutions were also re-determined. Examining the hypocentral distribution in detail, we found that the earthquakes occurring within the Philippine Sea plate are classified into three groups and that their focal regions form a triple-layered structure. The earthquakes in Group I, which are located at the uppermost part of the slab, were found to occur in the oceanic crust of the Philippine Sea plate from their waveform analysis. The focal mechanism analysis showed remarkable difference between the earthquakes in Groups II and III. The down-dip compression type events are predominant for the earthquakes in Group II, while most of the focal mechanisms in Group III showed the earthquakes are occurring under the down-dip extension. We proposed a model to explain the earthquake mechanism within the Philippine Sea plate, where the “forced unbending” by the underlying Pacific plate causes compressional and extensional stress fields in the upper and lower portion of the slab, respectively.

著者

茂木 清夫

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.3, pp.478-482, 1982-09-25 (Released:2010-03-11)

参考文献数

5

著者

小嶋 啓介 荒井 克彦

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.52, no.1, pp.213-218, 1999-06-30 (Released:2010-03-11)

参考文献数

116

著者

宇佐美 龍夫 関田 康夫 勝間田 明男 芦谷 公稔 鹿島 薫 橋口 能明 木下 幹夫 伊藤 純一

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.37, no.3, pp.506-510, 1984-09-25 (Released:2010-03-11)

参考文献数

10

被引用文献数

2

著者

溜渕 功史 山田 安之 石垣 祐三 高木 康伸 中村 雅基 前田 憲二 岡田 正実

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.62, no.4, pp.193-207, 2010-03-15 (Released:2012-03-26)

参考文献数

26

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We found eight M 5.1 characteristic earthquakes regularly occurring since 1966 on the plate boundary between the Eurasian plate and the Philippine Sea plate near Miyakojima Island, the Ryukyu Arc, Japan. The quake recurrence interval was 5.89 years in average, and the standard deviation was only 0.73 years. The accumulating stress presumably ruptured the same asperity enclosed by the creeping zone repeatedly. Also, we found three other groups of small repeating earthquakes of M 4, which occurred close to the hypocenters of the M 5 events. Those groups also occurred regularly and we can consider them to be ‘characteristic’ earthquake sequences. Now, we called those groups A, B, and C. It is not clear whether groups A and B had an intrinsic recurrence interval or if they influenced each other. However, two events of group C occurred within one week after the M 5 quakes, indicating that the M 5 events triggered the group C events whose asperity had suffcient strain energy. No earthquake exceeding M 7, which could change the recurrence intervals, has been observed on the subduction zone around the Ryukyu Islands. Therefore, there should be numerous characteristic earthquake sequences in other areas of the Ryukyu district. We expect that the next M 5 earthquake at 50 km depth on the plate boundary near Miyakojima Island will occur between September 2012 and July 2014 with 70% probability, using the small-sample theory with a log-normal distribution model. Moreover, the M 5 event may be accompanied by an M 4 quake that could rupture the asperity of group C within one week.

著者

武尾 実 阿部 勝征 辻 秀昭

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.32, no.4, pp.423-434, 1979-12-25 (Released:2010-03-11)

参考文献数

33

被引用文献数

1 3

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The source parameters of the Shizuoka earthquake (M=6.3) of July 11, 1935, are determined mainly on the basis of the close-in long-period seismograms. The epicenter and focal depth are redetermined at 35.0°N, 138.4°E and 27km. This earthquake represents a left-lateral strike-slip faulting on a plane dipping 70° toward 15°SE with a dimension of 11km(length)×6km(width). The average dislocation, rise time and stress drop are determined to be 1m, 1sec and 70 bars, respectively. The faulting at the depth of about 20km is very rare in Japan; because most of the major strike-slip events in Japan occurred near the ground surface. The theoretical ground motions expected from the above dislocation parameters are consistent with the leveling data and with the field data on the collapsed structures in the epicentral area.

著者

勝間田 明男 橋田 俊彦 三上 直也

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.52, no.1, pp.81-89, 1999-06-30 (Released:2010-03-11)

参考文献数

32

被引用文献数

2

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Old seismograms of the Tokyo earthquake in the Meiji era (June 20, 1894) were analyzed to retrieve source parameters. This earthquake gave considerable damage on the Tokyo metropolitan area. The focal depth was estimated to be about 50km or about 80km from S-P times of several seismograms observed at Tokyo. The magnitude, which was calculated from data of maximum amplitudes, was 6.6. The focal mechanism and the seismic moment were inferred from waveform fitting with seismograms observed by a Ewing-type strong motion seismograph and a Gray-Milne-Ewing-type seismograph. The estimated moment is 1-3×1018Nm (Mw=6.0-6.3). The earthquake is considered to have a nearly vertical nodal plane with N-S strike, and to have occurred in the Pacific plate or the Philippine Sea plate. Stress drop of the event was larger than the average value in the region.

著者

石橋 克彦

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.36, no.4, pp.668-671, 1983-12-25 (Released:2010-03-11)

参考文献数

17

被引用文献数

2

著者

田中 貞二 横田 治彦 岩田 孝行

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.41, no.2, pp.283-285, 1988-06-25 (Released:2010-03-11)

参考文献数

5

被引用文献数

3

著者

竹下 徹 奥平 敬元

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.4, pp.453-467, 1995-01-24 (Released:2010-03-11)

参考文献数

79

被引用文献数

1

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Dynamics and thermal modeling in low-pressure/high-temperature metamorphic belts (LPMs) are reviewed. LPM found in the world is formed under such P-T conditions that the pressure is lower than that of the aluminosilicate (Al2SiO5) triple point (about 400MPa), and the peak temperature ranges between 500 and 700°C. Such anomalously high temperatures at relatively shallow depth indicate that the geothermal gradient in the upper crust exceeded 50°C km-1 at the time of LPM formation. Although the steady state geothermal gradients in the upper crust necessary for the formation of LPM could be reached by continuously supplying a huge amount of magma in the upper crust [OXBURGH and TURCOTTE (1971)], such a steady state model is unlikely because of no observation of entire melting of the lower crust which is the outcome of the steady state model. Rather, transient heat sources such as the intrusion of magma, circulation of hot fluid, subduction of young oceanic plate or spreading ridge and convective thinning of the mantle lithosphere have been proposed to be the possible heat sources for LPM. Based on the heat transfer calculations, the duration of high-temperature condition by the intrusion of magma which is several kilometer wide, is less than 1Ma, and that by the circulation of hot fluid is poorly constrained. Even in the thermal model where the highest-temperatures in the country rocks attained by the intrusion of magma are assumed to be recorded as the metamorphic temperatures, the volume of magma necessary for the formation of LPM is more than 50% of the total volume of the crust [HANSON and BARTON (1989)]. Among these thermal models of LPM, subduction of young oceanic plate or spreading ridge is a likely model of LPM, not only because there are many occurrences of LPM evolved from accretionary sedimentary piles at trench, but because the ridge subduction can cause volcanism in the forearc [e. g., DELONG et al. (1979)] in addition to the anomalous heat supply to sediments from the asthenosphere. In order to further constrain the dynamics and thermal model of LPM in future, the P-T path and the duration of low-pressure type metamorphism must be accurately estimated petrologically, and the relative timing between metamorphism and deformation must be thoroughly investigated.

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.36, no.1, pp.83-107, 1983-03-25 (Released:2010-03-11)

参考文献数

63

被引用文献数

2

著者

松村 正三

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.2, pp.267-269, 1987-06-25 (Released:2010-03-11)

参考文献数

5

著者

馬場 久紀 飯塚 進 浅田 敏

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.143-153, 1994-08-14 (Released:2010-03-11)

参考文献数

25

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We studied the seismic activity in and around Iriomotejima Island, SW Ryukyu Arc, Japan, during the period from January 1992 through May 1993. In particular, two earthquake swarms, namely, the swarm which occurred off the SW coast of Iriomotejima Island late in August (SW swarm) and that occurred in the NW region of the Island in the middle of September 1992 (NW swarm), were investigated in detail in this paper. The data used in this study were restricted to “felt earthquakes” whose amplitudes were larger than 1gal. As a result, the number of events was not so large, but homogeneous in time and space.The spatial and temporal characteristics of these seismic activities are summarized as follows;1) A high swarm activity in the SW region continued several days. The focal zone extended to the NW-SE direction.2) The focal region of NW swarm migrated from off the NW coast of the Island to the inland area and then expanded to the surrounding areas.3) The focal zones extend in the NW-SE direction. And the vertical distribution of hypocenters shows a sharp seismic boundary plane. This is consistent with the predominant direction of the fault strikes and lineaments in this region.4) Some of the remarkable features observed in the later phases appear to represent reflected waves. These features suggest a possibility of the existence of sharp reflectors such as a magma reservoir beneath the region. However, no signs were seen for any surface volcanic activity.In consequence, it is considered that these earthquake swarms occurred under the stress field acting in the wide area of the SW Ryukyu Arc.

著者

高波 鉄夫 島村 英紀 本谷 義信

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.33, no.3, pp.269-287, 1980-09-25 (Released:2010-03-11)

参考文献数

12

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An earthquake swarm began south off Hakodate city on October 23, 1978. At the beginning, a seismological survey was temporarily set up in order to investigate a microearthquake activity in the neighbourhood of Minami-Kayabe which is about 30km northeast of the source area of the swarm.Seismicity around there were monitored by a seismological network of tripartite composed of a routine station ESH (Esan) of the Hokkaido University and two temporary unattended stations in which the portable long-period cassette tape recorders were equipped. These temporary observation systems were the OBS (Ocean bottom seismographs) which were modified for the land use.It is not a common experience that a temporary network caught the detail of the initiation of a swarm.In the first stage, the source area of the swarm is concentrated in a region of about 4×8km2 of area with a north-south trend. Several weeks later another concentrated area is added at several kilometers southeast of the former region. Therefore, we can refer to the former in early about 40 days at the beginning stage of the whole activity off Hakodate which has been active for more than a year.Item of the present paper is concentrated to the result of our seismological observation at the early stage of a relatively short period from October 23 through the end of November 1978.In the first stage of about 40 days, the activity can be further divided into three periods. In the first period, which is five days since the appearance, very small shocks gradually increased in number.When the number of earthquakes increased abruptly the second period began. It is midday of October 27, 1978. This was the most active period in the first 40 days.The third period began on October 29, when the activity began decreasing.The m-values of Ishimoto-Iida's equation were, m=2.8 for the first period, m=1.6 for the smaller events and m=2.0 for the larger events in the second period, respectively, by the monitored records of ESH. The value for the third period could not been obtained easily for the difficulty in applying the Ishimoto-Iida's relationship.For the large earthquakes (250μ kines-2500μ kines in the maximum velocity amplitude), the m-value was obtained by the records at the nearest station OBS-1 for the period from Oct. 25 through Nov. 8, 1978. Its value was m=2.8.No earthquake with magnitude more than 3.5 occurred during the first 40 days though the total number of the recorded earthquakes is about 3700 or more.

著者

寺島 敦 松本 利松

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.1, pp.81-88, 1984-03-25 (Released:2010-03-11)

参考文献数

11

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In June and August of 1980 two separate swarms of microearthquakes occurred in the proximity of the Tavera Reservoir, Dominican Republic. The earthquakes were located along the Tavera Fault that runs through Tavera Reservoir. These swarms were observed after abrupt changes of water level occurred. A gradual increase of water level during the period of September through November, however, did dot produce induced earthquakes except sporadic events despite the fact that the highest water level surpassed the peak elevations of two abrupt changes. It was inferred from these observations that the induced seismicity was sensitive to the abrupt changes, especially a rapid draw-down of water level rather than or in addition to the water level itself. The foci of the second swarm in August was distributed adjacent to the area occupied by the first swarm in June, implying that the rock fracture propagated from one zone to another during these two active swarm sequences.

著者

中村 浩二 荒井 賢一

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.48, no.4, pp.451-461, 1996-03-12 (Released:2010-03-11)

参考文献数

6

被引用文献数

2

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A tsunami was generated by the 1994 Hokkaido Toho-Oki earthquake and was observed at tidal stations on the Pacific coast of the Japanese Islands. It was observed also at several tidal stations on Hokkaido coast of the Okhotsk Sea, where the arrival of the initial wave was recorded earlier than the expected time: for example, the initial motion of the tsunami was recorded at Utoro 17 minutes after the mainshock, while that the theoretically expected tsunami arrival time from the source in the south sea region of Shikotan Island is 80 minutes after it. We tried to estimate the location of the source of the early coming waves by drawing the inverse refraction diagram from each station. We suggest two probable locations of the source; one is the area 80 kilometers north of Abashiri, and the other is the area 40 kilometers north of the tip of Shiretoko Peninsula. The seismic activity at both of those areas is poor. So, we cannot judge that the early coming waves were generated by some another events. Both of those areas are situated in the continental slope regions and with steep slopes. We suppose that a land slide at either of those areas caused the early coming waves.

著者

弘瀬 冬樹 中村 綾子 長谷川 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.55, no.3, pp.249-260, 2002-12-15 (Released:2010-03-09)

参考文献数

27

被引用文献数

11

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We found a clear b-value variation associated with the rupture of asperities based on investigations of spatial and temporal distributions of frequency-magnitude relation for earthquakes in the northeastern (NE) Japan subduction zone. We used the Tohoku-University earthquake catalogue in the period from January 1, 1981 to October 3, 2001 after correcting artificial magnitude shift and removing artificial events. Spatial distribution of b-value is compared with the locations of asperities estimated on the plate boundary east off NE Japan. Estimated b-value decreases with increasing depth. Anomalously high b-values are observed in two areas off-Iwate and off-Fukushima regions, and asperities do not intrude into them. Temporal variation of b-value for presently analysed six asperities shows a remarkable increase in b-value after the rupture of each asperity. Then the b-value decreases gradually. These observations suggest that b-value reflects the stress change occurring in the vicinity of the asperities.