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.

著者

中西 一郎

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.59, no.3, pp.237-238, 2007-03-15 (Released:2013-08-05)

参考文献数

21

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.15, no.9, pp.217-224, 1943-09-18 (Released:2010-11-17)

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.8, no.6, pp.309-311_1, 1936-06-15 (Released:2010-03-09)

著者

奥澤 保 塚原 弘昭

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.53, no.3, pp.241-253, 2001-03-25 (Released:2010-03-11)

参考文献数

31

被引用文献数

5

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Many small earthquakes occurred in the Matsushiro area in a period from 1965 to 1967. This is called “Matsushiro Earthquake Swarm”. The swarm earthquakes are interpreted as a result of deep ground water intrusion into the focal area. At the hardest time of the crustal movement, water flow from pre-existing springs increased, and many new springs appeared along a hidden fault zone formed by the swarm earthquakes. Some of springs are still alive and have peculiar chemical compositions. The deep ground water must have caused the earthquake swarm. We show the characteristics of the deep ground water through analyzing chemical composition. Our measured data and many published data show that the deep ground water obtains Ca2+ from rocks and loses Na+ during its upwelling migration through the fault zone of Matsushiro Swarm Earthquakes. The data also show that the major components of Cl- and (Na++Ca2+) have a liner relation in concentrations, although every spring water has different concentrations of Cl- and (Na++Ca2+). It is interpreted in terms of mixing deep ground water with shallow ground water at defferent ratios. The concentrations of the major ions of the deep ground water are estimated from both of our measured data and compiled data using the liner relation, e. g., Na+: 310meq/l, Cl-: 330meq/l. Analysis of our measured data also reveals that the small temporal variation in the concentration of Ca2+ in a short period such as several months is attributable to the reaction between the ground water with CO2 and surrounding rocks.

著者

山科 健一郎 中村 一明 福留 高明 佐藤 魂夫 田中 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.38, no.1, pp.81-91, 1985-03-25 (Released:2010-03-11)

参考文献数

18

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Based on a few tens of photographs, height change of Kyuroku-shima Island, which locates very close to the focal region of the Japan Sea earthquake (M=7.7) on May 26th, 1983, is analyzed. 1) The island and adjacent small islets are considered to have subsided by about 30-40cm associated with the 1983 earthquake. The average offset obtained by 13 reliable photographs is 32±9cm. 2) Precursory deformation and secular change of the height were not found during 1964 through 1982. No detectable deformation was caused by largest aftershock (M=7.1) on June 21, 1983, and other aftershock activity. 3) Coseismic tilt and local collapse were not observed in the island. 4) In some cases, a height can be inferred even from snapshots with the error less than several percents. Crustal uplift and subsidence more than 10-20cm may be possible to be detected photographically at the seashore and lakeside.

著者

伊藤 潔 梅田 康弘 黒磯 章夫 村上 寛史 飯尾 能久

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.2, pp.301-311, 1986-06-25 (Released:2010-03-11)

参考文献数

16

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The source characteristics of the Japan Sea earthquake, May 26, 1983 (M=7.7) is inferred from the seismic observation system with wide-frequency and large-dynamic range at the Abuyama Seismological Observatory. The duration of oscillation of the long-period low-gain seismogram (T0=25s) is much longer than those of other earthquake with nearly the same magnitude and nearly the same epicentral distance, which implies that the earthquake is a multiple shock. The relationship between a multiple shock and duration of oscillation is more clearly indicated in the figure of double amplitude envelope to eliminate the difference in amplitude by magnitude and focal mechanism. This simple method is applicable to detect multiple shocks in seismograms at one station, especially in historical seismograms with a few instrumental records.Seismograms of the main shock of the Japan Sea earthquake recorded by Wiechert seismographs and those of middle-period (T0=10s) low-gain velocity seismographs show a clear onset of the second event at about 22 seconds after the first arrival. Since no such second arrival is seen on the seismograms of the aftershocks at the same station, the phase is not a crustal phase but a P-wave arrival of the second event of the main shock.The main shock recorded by the middle-period low-gain velocity seismograph contains more complicated high frequency waves than the largest aftershock. This indicates that the rupture process of the main shock is much complicated compared with that of the aftershock. Further, comparing the spectrum of the first event of the main shock with that of the second event, the average amplitude at a low frequency (5-10 s) of the first event is smaller than the second event, while that at high frequency (1-2s) is larger than the second event. This suggests that the main shock is composed of double events of different rupture type; the rupture of the first event is smaller and radiated much high frequency waves than the second event.

著者

海野 徳仁 伊藤 喜宏 五十嵐 俊博 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.53, no.3, pp.263-268, 2001-03-25 (Released:2010-03-11)

参考文献数

25

被引用文献数

2 3

著者

石橋 克彦 佐竹 健治

出版者

日本地震学会

雑誌

地震 (ISSN:00371114)

巻号頁・発行日

vol.50, pp.1-21, 1998-03

被引用文献数

10

著者

加藤 研一 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.49, no.1, pp.75-83, 1996-05-24 (Released:2010-03-11)

参考文献数

27

被引用文献数

1

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Direction of rupture propagation φ and fault length L for the 1994 Sanriku-Haruka-Oki earthquake are evaluated from the azimuthal dependence in duration of strong ground motion observed at eleven stations along the Pacific coast of Tohoku and Hokkaido region. After defining the strong motion duration D as the time interval between onset of S wave and 85% of cumulative power curve derived from 5 to 10Hz band-pass filtered accelerogram, the azimuthal dependence of D is examined. We find that D systematically shows directivity: D is the shortest at northern part of Tohoku and the longest at southern part of Tohoku and eastern edge of Hokkaido. By making use of the directivity on observed strong motion durations, we apply the method by IZUTANI and HIRASAWA (1987) to deducing φ and L together with VR/β, where VR and β are rupture velocity and S wave velocity. Assuming that rupture initiated from the epicenter determined by the Japan Meteorological Agency (JMA), we obtain L/VR=53, VR/β=0.62, and φ=W9°N (case 1). This result indicates that the rupture was headed toward northern part of Tohoku, and terminated near the western end of aftershock area. Detailed source-process inversion [for example, SATO et al. (1996)] suggests that main rupture nucleated near the center of aftershock area, corresponding to the epicenter determined by Harvard University. We redo the calculation assuming that the rupture initiated from the Harvard epicenter, then resulting in L/VR=28, VR/β=0.71, and φ=W18°N (case 2). This result also indicates that the rupture propagated toward northern part of Tohoku, and terminated at the western end of aftershock area. SATO et al. (1996) suggest that this earthquake consists of threestage rupture process: the first and the second sub-events corresponding to JMA and Harvard epicenter, respectively, and the third sub-event located near the western end of aftershock area at the distance of about 50km from Hachinohe city. The location where rupture terminated in both cases of this study is consistent with the location of the third sub-event, confirming that the rupture extended to the western end of aftershock area.

著者

力武 常次

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.4, pp.451-466, 1989-12-24 (Released:2010-03-11)

参考文献数

10

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Anomalous phenomena precursory to the 1891 Nobi earthquake of magnitude 8.0 are collected mostly based on the existing results of the enquiry investigation conducted soon after the earthquake. Precursor data amounting to 202 in number become available along with their precursor times. They are rumbling or detonation, anomalous animal behaviour, earthquake light, changes in underground water/hot springs and so on.It appears that the number of earthquake precursor tend to increase at about 100 days before the main shock. About 10 days preceding the shock, the increasing rate becomes much accelerated reaching a frequency peak having a precursor time of 1 day or so. Such a tendency of precursor appearance is much the same as that for the 1923 Kanto, 1944 Tonankai and 1978 Izu-Oshima Kinkai earthquakes although slight differences may be observed. The tendency that the number of precursor decreases as the distance between the epicenter and an observation spot increases is also confirmed.In light of these precursors detected by human sense in association with the Nobi earthquake as well as other large earthquakes in Japan, attention should be paid to precursors of this class along with geophysical precursors in future earthquakes.

著者

草野 富二雄 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.43, no.4, pp.459-469, 1990-12-24 (Released:2010-03-11)

参考文献数

20

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Aftershock activity of the 1987 Chiba-ken Toho-oki earthquake (M6.7) is investigated using JMA data. It is found that aftershocks during two weeks just after the main shock occurred mostly in a region to the east side of the fault plane which is nearly north-south direction with a steep dip to the east. However, aftershock activity in the area to the west side of the fault plane became high since the beginning of January 1988. The contrast between spatial distribution of aftershocks in December 1987 and that after January 1988 is conspicuous. The later activity was concentrated to a rather small area and the largest aftershock occurred on 16 January in the active region. The mechanism of the largest aftershock was reverse type in contrast to the mechanism of the main shock which was strike slip type. Further, pattern of temporal decrease of aftershock activity deviated notably from the Omori's formula when the later activity was started. All these characteristics suggest that most earthquakes which occurred in the region to the west of the fault plane of the main shock after January 1988 are not the so-called aftershocks in a narrow sense, but that they represent an appearance of a new fracture, which occurrence might be caused by the stress concentration due to the fault motion of the main shock. The phenomenon that aftershock activity in the either one side against a fault plane is higher than that in the other side is frequently observed, even for fault motions of strike slip type. It is interesting to note that seismicity before the main shock was also asymmetrical, i. e. it was active in the region to the west of the fault plane of the 1987 earthquake. The seismicity in the recent one year also seems to be active in the west region. These features may show that the western block to the fault plane has taken a positive part in the accumulation process of stress in the focal region of the 1987 Chiba-ken Toho-oki earthquake.

著者

井上 直人 田中 靖之 伊藤 陽之 岩野 祥子 北田 奈緒子 福田 洋一 竹村 恵二

出版者

日本地震学会

雑誌

地震. 2輯 (ISSN:00371114)

巻号頁・発行日

vol.57, no.1, pp.45-54, 2004-08-25

著者

伊東 敬祐

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.157-167, 1998-03-31 (Released:2010-11-17)

参考文献数

40

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Earthquakes are complex phenomena. The notion of self-organized criticality (SOC) is recently used to explain various kinds of seismological relations expressed as power-laws, such as the size-distribution, the fractal spatio-temporal distribution and the decay of aftershocks. It is often claimed that earthquakes are not predictable if they are critical phenomena It is true that they are not predictable if the earth is at exact criticality. The notion of SOC. however, is not static but is dynamic. The crust gently approaches criticality and breaks down to generate a large earthquake. There are a variety of SOC models of earthquakes. In all of them, most of small and intermediate earthquakes occur while the system is at subcritical state approaching the exact criticality. Large earthquakes mostly occur near the criticality or at the supercritical state. Therefore, large earthquakes differ from small and intermediate ones even in the statistically scale-free SOC models. Large earthquakes in nature also are expected to be unusual events occurring at critical or supercritical states at which physical properties are extemely abnormal. Different SOC models exhibit different precursor phenomena before large events, as observed precursors differ from event to event. There cannot be universal methods to predict every large earthquake, but individual large earthquakes can be expected to have some precursors. It may be careless to reject observed precursors on a reason that they were not always observed before large earthquakes.

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.29, no.2, pp.117-126, 1976-05-15 (Released:2010-03-11)

参考文献数

17

被引用文献数

1

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A fault model of the 1974 Izu-Oki Earthquake was studied by the vertical crustal movement and the distribution of the after shocks.An assumed fault type is the right lateral pure strike slip, and the fault parameters are as follows, length=15km, width=8km, dip angle=75°, and dislocation=130cm.The stress field in the southern part of the Izu peninsula deduced from this fault motion is the north-south directional compressive field. This stress field represents that the Izu peninsula is compressed from south to north by the movement of the Philippine Sea Plate.