著者

鷺谷 威

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.111-120, 1999-06-30 (Released:2010-03-11)

参考文献数

17

被引用文献数

2 3

---

Conventional triangulation and leveling data are analyzed to estimate crustal movements associated with the 1948 Fukui earthquake and its fault model. Horizontal displacement vectors at 84 triangulation points and vertical displacements of 82 leveling benchmarks are inverted to estimate slip distribution on the fault plane. Although two surface traces of faults were found after the earthquake, most of the seismic moment was released from a main fault on the west, and an eastern sub-fault played only a complementary role. The dip angle of the main fault is not well constrained. However, geodetic data are fairly consistent with an assumption of a vertical fault. Estimated fault mechanism is mostly left-lateral strike slip with the maximum slip of 6m. The seismic moment of the Fukui earthquake is estimated as 2.4×1019Nm (Mw=6.8), which is consistent with another estimation based on seismic data. The Fukui earthquake was comparable to the 1995 Kobe earthquake in its size, but the heterogeneity of slip distribution is different each other. The Fukui earthquake fault had a much longer preparatory period before the 1948 event, and fault strength might be completely recovered before the earthquake, which resulted in a rather homogeneous slip distribution. In the case of the 1995 Kobe earthquake, a short recurrence time along the Rokko-Awaji fault after the 1596 Keicho-Fushimi earthquake might result in a rather heterogeneous slip distribution.

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.21, no.2, pp.142-143, 1968-08-30 (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.5, no.10, pp.607-626, 1933-10-15 (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.29, no.2, pp.179-190, 1976-05-15 (Released:2010-03-11)

参考文献数

12

---

The source mechanisms of eight tsunamis generated off Fukushima, the Pacific side of northeast Japan, in May to November 1938 are re-studied, making use of tide gauge records. The source areas for each tsunami inferred from the inverse refraction diagrams are shown in the bathymetric charts. The source locations moved to the north direction along the continental shelf, and the north end was in contact with the source area of the tsunami at Nov. 3, 1936. Among these tsunamis, three tsunamis were recorded in a downward direction at Onahama located near the sources, but other tsunamis began with an upward motion. According to the seismic wave data, the tsunamis of downward and upward initial motions correspond to the normal and reverse fault earthquakes, respectively. Tsunamis accompanied by earthquake of the normal fault type were generated later than those for the reverce fault earthquakes, and these source areas are located in the deep sea-bottom side. The source lengths of tsunami are 60-130km, corresponding to earthquake magnitude. A whole length from north to south ends of the sources is 200km.The calculated sea-level disturbances at the sources for each tsunami are in the range of 10-50cm which the heights nearly agree with the seismic fault models. The whole volume of the displaced water in the tsunami sources is 13×1015cm3 which is comparable to that of the 1968 Tokachi-oki tsunami (tsunami magnitude of Imamura-Iida scale m=2.5).

著者

佐藤 隆司 楠瀬 勤一郎 長 秋雄 木山 保 山田 文孝 相澤 隆生

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.50, no.1, pp.57-65, 1997-05-28 (Released:2010-03-11)

参考文献数

22

---

Crustal stress measurements by the hydraulic fracturing method were carried out using a 1000m- and a 100m-deep boreholes drilled at Inagawa town, Hyogo prefecture, where earthquake swarm activities with very shallow hypocenters have intermittently occurred since July 1994. On borehole televiewer record, borehole breakouts were clearly observed at a number of depth intervals of the 1000m-deep borehole. The borehole breakout data as well as the hydraulic fracturing data was used to estimate orientation of the maximum horizontal compressive stress.Magnitudes of the horizontal stress down to 700m in depth are comparable to the standard stress gradients with depth in western Japan derived by TANAKA (1986). On the other hand, the maximum and minimum horizontal compressive stresses at about 950m in depth are about 70MPa and 40MPa, respectively, which are about twice as large as the standard stress gradients with depth in western Japan. The maximum horizontal compressive stress below 600m in depth is generally oriented E-W to NW-SE.

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.41, no.4, pp.613-614, 1988-12-25 (Released:2010-03-11)

参考文献数

5

被引用文献数

1

著者

市橋 正生

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.64, no.1, pp.23-32, 2011-08-25 (Released:2011-10-18)

参考文献数

24

被引用文献数

1

---

The relationship between the days of earthquake in Japan and its vicinity and the Be-7 concentrations in the surface air at Takasaki were statistically analyzed. A day when one or more earthquakes of M 5 or greater occurred in Japan and its vicinity was defined as a “day of earthquake”. Earthquakes which were deemed aftershocks were not included in the analysis. In order to avoid the effect of seasonal variation, the residuals obtained by deducting 31-day moving averages from Be-7 concentrations and those obtained by deducting the ‘21-day’ moving averages of the periods from −15 to +0 days and from +11 to +15 days were analyzed. The ‘21-day’ moving averages were also calculated to avoid the effect of aftershocks. Rank-sum tests of the residuals showed that the Be-7 concentrations decreased from the 31-day and ‘21-day’ moving averages on days of earthquake. A binomial test showed that there were significantly more days of earthquake when the Be-7 concentrations were smaller than the medians of Be-7 concentrations for the 31-day periods (from 15 days before to 15 days after days of earthquake) than those when the Be-7 concentrations exceeded the medians. These suggest that the Be-7 concentrations decrease on days of earthquake. It is noted that the Be-7 concentrations on days of earthquake decreased on days of both precipitation and non-precipitation, respectively.

著者

阿部 勝征

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.3, pp.369-377, 1999-12-25 (Released:2010-03-11)

参考文献数

46

被引用文献数

13

---

A method for determining the tsunami magnitude Mt from tsunami run-up heights is developed by using the Abe's (1989) relation which has been employed for estimating run-up heights from earthquake magnitudes. The magnitude Mt is estimated from the relation, Mt=2logHm+6.6, where Hm is the maximum value of the local-mean run-up height in meters and the logarithmic mean of heights is taken over a distance of about 40km along a coast. Except for unusual events, the moment magnitude can be estimated from Mw=Mt-2C, where C=0 for tsunamis in the fore arc and C=0.2 for tsunamis in the back arc. For 12 large tsunamis that occurred around Japan from 1894 to 1998, Mw estimated from Mt is found to be essentially equivalent to that estimated from seismic waves. The present method is applied to determining Mt for 21 historical tsunamis that occurred around Japan on and after the 15th century. There are 13 large tsunamis with Mt=8 or over for the period from 1498 to 1893.

著者

杉山 雄一

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.43, no.3, pp.439-442, 1990-09-24 (Released:2010-03-09)

参考文献数

18

被引用文献数

4

著者

橋本 学

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.521-530, 1996-03-12 (Released:2010-03-11)

参考文献数

23

被引用文献数

2 3

---

We calculate static stress changes for the fault model derived from geodetic data before and after the magnitude=7.2 Kobe earthquake of January 17, 1995 in order to examine the possible correlation between changes in seismicity in the surrounding regions and stress changes.The Coulomb failure function (CFF) for right lateral slip on NE-SW or nearly E-W trending vertical faults may increase in the north of the Arima-Takatsuki Tectonic Line, where the activation of seismicity is observed. CFF for left lateral slip on NW-SE trending vertical faults may also increase around the Yamasaki fault, northwest of Kobe, which is consistent with the activation of seismicity there. In the northern Kinki district, where seismicity became a little bit lower, CFF is predicted to decrease. CFF may change a little in the Wakayama region, where significant seismicity changes are not observed.The Kobe earthquake may have loaded the Arima-Takatsuki Tectonic Line, segments of the Median Tectonic Line in Wakayama and Tokushima and westward dipping thrusts in the Osaka plane. Therefore we should carefully monitor the crustal activity around these tectonic lines.

著者

阿部 邦昭

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.49, no.1, pp.11-17, 1996-05-24 (Released:2010-03-11)

参考文献数

8

---

Focusing effect of islands on the 1983 Nihonkai-chubu (central part of the Japan Sea) earthquake tsunami was identified at eight coasts facing to islands from peak formations of the maximum inundation heights. Defining parameters of the peak height (H) at a coastal focus, the background average height (H0), the peak width (Wd), the coastal focus distance from the island (L) and the island size (L0), we discussed relations among them. As the result peak width Wd is approximated asWd/L0=0.43 (L/L0)1.0Amplification ratio H/H0 is about 1.5 for islands of epicentral distances smaller than 400km and shows an increase with the epicentral distance for islands of epicentral distances larger than 400km. These facts are explained as a focusing effect of islands on tsunamis, in which incident wave, refracted in a sloped region around the island after divided into two, superposes on each other in the back side. In islands distant from the source the incident wave is coherent and the amplification ratio increase. The amplification ratio and relative peak width are compared with those in the another focusing effect, previously found on the 1993 Hokkaido nansei-oki earthquake tsunami. The similar proportionality of peak width and amplification ratio between two tsunamis suggest that the amplification is caused by the same mechanism.

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.50, no.3, pp.291-302, 1997-12-12 (Released:2010-03-09)

参考文献数

37

被引用文献数

1

---

The 1782 August 23 Ten'mei Odawara earthquake, magnitude 7.2-7.3, is one of the three M7-class earthquakes that occurred beneath the Odawara area on the northwestern coast of Sagami Bay, the Pacific coast of central Japan, since the 17th century. Two other events, the 1633 Kan'ei and 1853 Ka'ei Odawara earthquakes, were definitely accompanied by tsunamis and their rupture zones are estimated to have lain just beneath Odawara, a seashore city in the area, extending both inland and offshore directions. This estimation is in agreement with the fact that the 1633 and 1853 earthquake ground motions at Odawara were very strong. On the other hand, the 1782 Ten'mei Odawara earthquake had been considered to have been non-tsunamigenic after critical readings of historical documents by a few investigators, and its source region had been inferred to be situated inland north of Odawara city. TSUJI (1986), however, claimed that the 1782 earthquake generated a tsunami and estimated that the tsunami height was 4 m at a fishing village, Ajiro, based on the examination of two newly found historical documents. He estimated a nearly 30 km-long tsunami source region south off the Odawara coast in addition to the inland rupture zone. Tsuji's interpretation yields a north-south extent of faulting too long to be consistent with an M7-class earthquake. It also conflicts with the fact that the 1782 earthquake ground motion was not the heaviest at Odawara, which strongly suggests that Odawara was not just above the rupture zone. TSUJI (1986) reported at the same time that Atami, a seaside town between Ajiro and Odawara, was not struck by a tsunami in 1782, which seems unreasonable from the viewpoint of tsunami behavior; actually, at the time of the 1633 earthquake the estimated tsunami height at Atami was 4-5 m, whereas that at Ajiro was 3-4 m. Whether the 1782 Ten'mei Odawara earthquake generated a tsunami or not is very important for not only the estimation of its rupture zone, but also the seismotectonics of the series of Odawara earthquakes. TSUJI (1986) drew his conclusion by very intricate interpretation of two historical documents which don't give any explicit description of a tsunami at Ajiro in 1782 at all. In this paper I reexamine the two documents more carefully and address the difficulties in Tsuji's conclusion. By referring to various materials describing the history of Ajiro village from the 17th to the mid-19th centuries, I clarify that TSUJI (1986) misread vague, rather general, descriptions of huge waves due to storms as a tsunami. Thus, I reject the suggestion that the 1782 Ten'mei Odawara earthquake generated a tsunami, and I conclude that its source region is inland north of Odawara city.

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.12, pp.336-341, 1943-12-18 (Released:2010-11-17)

被引用文献数

1

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.24, no.4, pp.369-371, 1972-01-31 (Released:2010-03-11)

参考文献数

2

著者

都司 嘉宣 上田 和枝 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.51, no.1, pp.1-17, 1998-07-03 (Released:2010-03-11)

参考文献数

48

被引用文献数

3

---

From midnight of January 27, 1700 to noon of the next day, abnormal sea level changes were recorded at several locations on the Pacific coast of Japan. We previously interpreted these as tsunamis from a giant earthquake in the Cascadia subduction zone, off the west coast of North America. In this paper, we report our detailed examinations of the original documents recording the tsunamis, including the reliability of the documents themselves. The tsunamis were described in six independent documents, mostly local government records. No one was injured or killed at any location. In Miyako, 20 houses were burned and 13 houses were destroyed by the tsunami. At Otsuchi, a few houses and rice paddies were damaged. In Tanabe, the government storage house was inundated. The tsunamis were first noticed just before midnight of the 27th at Miyako and Otsuchi, and the next morning at the other localities. We estimated the tsunami heights from descriptions in the documents, after accounting for tide levels and vertical crustal movements of coasts since 1700. The latter correction is difficult and the uncertainty is large. The estimated tsunami heights were: 4m at Kuwagasaki, 3.2m at Tsugaruishi, both in Miyako, 3.3m at Otsuchi, 1m at Nakaminato, 1.0-1.7m at Miho, and 3.3 and 5.4m at two locations in Tanabe. We also examined the weather records for January 26-29 and found no abnormal description, ruling out the possibility of meteorological origin. Lack of regional earthquakes on these days and the tsunami height distribution indicate that the tsunami came across the Pacific Ocean. We then estimate the tsunami magnitude, Mt, for each possible tsunami source around the Pacific. The result shows that the size of earthquake that generated the tsunami was M9 wherever the source was. We examined historical data and paleoseismological results in the possible regions and confirmed that the tsunami source was the Cascadia subduction zone, and that the origin time was around 9PM on January 26, 1700 local time.

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.19, no.3, pp.226-227, 1966-12-25 (Released:2010-03-11)

参考文献数

2

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.61, no.Supplement, pp.357-364, 2009-07-31 (Released:2013-11-21)

参考文献数

96

被引用文献数

1 2

---

History of studies of intraslab seismicity and its generation mechanisms, since the work by Wadati, is reviewed. Through the initial stage of studies of morphology of the intraslab seismicity, there followed the stage of discussion of focal mechanisms and terminal depths by mechanics and temperature of the slab. In 1970s, double seismic zones were discovered and their generation mechanisms were discussed in terms of bending or thermal stresses. In recent years, to overcome a difficulty that very high pressure prevents intraslab seismicity, dehydration embrittlement and phase transformation have been invoked for the mechanisms of intermediate and deep earthquakes, respectively. If the intermediate seismicity represents dehydration, it may give us a key to understand the distribution of fluids to the upper plate and to the seismogenic interplate thrusts, and finally to understand tectonics and volcanism in subduction zones.

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.2, no.5, pp.326-328, 1930-05-15 (Released:2010-11-17)

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.35, no.3, pp.427-433, 1982-09-25 (Released:2010-03-11)

参考文献数

2

被引用文献数

2

---

An anomalous crustal uplift was observed at the west coast of Boso Peninsula. The crustal uplift began at the same time as the mining of mountain rock which began about ten years ago.It seems that the crustal uplift is the result of the elastic recovery deformation of the earth's crust caused by the man-made surface unloading.An elastic modulus of the uppermost earth's crust estimated by the total amounts of crustal uplift and mined rock is about 1-2×1011dyne/cm2.

著者

大見 士朗 和田 博夫 伊藤 潔

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.54, no.3, pp.415-420, 2001-12-25 (Released:2010-03-11)

参考文献数

8