著者

飯塚 進

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.4, pp.365-374, 1976

被引用文献数

1

---

There is a remarkable discrepancy in the previous results on the temporal variations in seismic wave velocities related with the Matsushiro earthquake swarm that have been studied by many investigators. A result from the <i>V_p</i>/<i>V_s</i> method shows co-seismic anomaly, while all the data from the P-residual method indicate precursory anomaly.<br>To make clear the cause of this discrepancy, temporal changes in <i>V_p</i>/<i>V_s</i> ratio was reexamined by using the different set of data source from previous studies. Two kinds of velocity anomalies, namely, precursory and co-seismic or post-seismic anomaly were detected as the same as in the previous investigations.<br>Combining the present data with the data from previous studies, it was inferred that the precursory anomaly in seismic velocities might occur mainly in the zone of lower crust to the uppermost mantle, while the co-seismic or post-seismic anomaly might occur in the upper part of crust whose depth is not greater than 10km, underneath at and adjacent area of the Matsushiro earthquake swarm. In other words, the anomalous zone must have migrated from the deeper parts to the upper crust about the time when the swarm began.<br>The origin of these two anomalies were interpreted by a new model which takes thermal effects into consideration for earthquake occurrences.

著者

長谷川 昭 堀内 茂木 植木 貞人 西澤 あずさ 松澤 暢 海野 徳仁 堀 修一郎 稲盛 隆穂 松本 聡 浜口 博之 高木 章雄 田中 和夫 鈴木 将之 末広 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.42, no.2, pp.161-169, 1989-06-24 (Released:2010-03-11)

参考文献数

17

被引用文献数

1 1

---

A seismic refraction experment was carried out around the Bandai volcanic area, the southern part of the Tohoku District, by using a large capacity (9 liter air chamber) marine airgun. Shallow crustal structure (down to about a 4km depth) obtained along the 30km-length profile shows the swelling of the second layer with P-wave velocity more than about 4.0km/s just beneath Bandai volcano in parallel to the surface topography. The swelling of the second layer by about 1km is in good agreement with that of the basement estimated from the Bouguer anomaly.Seismic signals from the surrounding telemetered stations of Tohoku University at epicentral distances from 10km to 230km, are continuously recorded during the airgun experiments. In the stacked records we can detect the clear first P arrivals from the airgun shots at the stations with distances ranging up to 150km, which shows the usefullness of the marine airgun for studying the crustal structure on land. Anomalously late P arrivals or unclear P arrivals are observed for the ray paths which cross active volcanoes. This result and the shallow crustal structure obtained along the refraction profile suggest the existence of the anomalous zone beneath Bandai volcano at depths deeper than about 4km.

著者

小林 昭夫 弘瀬 冬樹 堀川 晴央 平田 賢治 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.70, pp.221-231, 2018

被引用文献数

2

著者

那須 信治

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.34, no.special, pp.123-134, 1981-09-25 (Released:2010-11-17)

被引用文献数

1

著者

小山 順二 都筑 基博

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.66, no.4, pp.83-95, 2014-03-25 (Released:2014-05-20)

参考文献数

59

被引用文献数

1 1

---

After the 2011 Tohoku-oki megathrust earthquake of Mw 9.0, we observed tens of thousands of inland and volcanic earthquakes all over the Japan Islands, which are not confined within the aftershock area of off the Pacific coast of Tohoku region. This reminds us to evaluate the earthquake activity in a much wider sense, discarding an ordinary idea of the foreshock-mainshock-aftershock activity within a limited aftershock area of a particular earthquake. There occurred several megathrust earthquakes worldwide in the last one hundred years. We have studied their significant events before and after the earthquakes based on our new hypothesis on the earthquake generating zone with the distinct difference between Along-dip Double Segmentation (ADDS) and Along-strike Single Segmentation (ASSS). In summary, some of significant aftershocks (larger than Mw 7.5) of ADDS megathrusts are those (Type I) in and near outer-rises, where some are dip-slip normal faultings and some are strike-slip faultings within subducting oceanic plates with component of normal fault. These outer-rise earthquakes are considered to be controlled by the slab-pull of descending slabs of oceanic plates induced by the reduction of plate couplings by megathrusts. In addition, some are also significant (Type II) along the plate interfaces within aftershock areas and those extending aftershock areas similarly to the corresponding megathrusts. On the other hand, aftershocks of ASSS occurred in and near corresponding aftershock areas and significant and or disastrous outer-rise events are rare. Some large (not significant) inland earthquakes are also known for both ADDS and ASSS megathrusts. All these results are not dependent on whether the subduction geometry is oblique or orthogonal.

著者

竹内 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.27, no.3, pp.274, 1974-09-30 (Released:2010-03-11)

参考文献数

2

著者

表 俊一郎

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.15, no.5, pp.101-113, 1943

著者

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.4, pp.645-652, 1986-12-25 (Released:2010-03-11)

参考文献数

6

被引用文献数

2

---

We observed ultramicroearthquakes with a magnitude (J. M. A. scale) down to -3, by the highly sentitive aftershock observation of the Western Nagano Prefecture Earthquake of Sep. 14, 1984 (M=6.8).The seismometer used is a 2Hz velocity-type transducer with flat response up to about 1kHz. Signals were recorded continuously on an analog data recorder. The overall frequency response of the observation system is flat from 2 to about 270Hz (-3dB point). Its highest sensitivity for the ground velocity was 18300V/(cm/s).About 10, 000 earthquakes were recorded for the period of the observation. From them, the shocks of which S-P times <0.6s were chosen and analyzed. The total number of the earthquakes analyzed is 183. Their frequency-magnitude distribution and frequency-S-P time distribution were investigated. The earthquakes analyzed are distributed in magnitude down to -3. Their S-P times are distributed down to 0.05s.

著者

岩城 麻子 岩田 知孝 関口 春子 浅野 公之 吉見 雅行 鈴木 晴彦

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.61, no.4, pp.161-173, 2009

---

We studied the source model and the underground velocity structure model for quantitative estimation of long-period (3-20s) ground motion in the Oita Plain due to a hypothetical Nankai earthquake. First, the deep subsurface velocity structure of the Oita sedimentary basin was validated by a long-period ground motion simulation of the 2000 western Tottori earthquake records. The simulated waveforms reproduced the amplification and duration of the observed waveforms and peak periods of pseudo response spectra at strong motion stations both in and out the Oita Plain reasonably well. Then we combined the subsurface velocity structure with a crustal velocity structure and performed long-period ground motion simulations of a Nankai earthquake by a three-dimensional finite-difference method. The source model has a total area of 34,000 km<SUP>2</SUP> with total seismic moment of 6.24&times;10<SUP>21</SUP> Nm (<I>M</I><SUB>W</SUB> 8.5). In addition to the scenario in which rupture propagates from the east (east-hypo model) that have been generally accepted, we investigated another from the west (west-hypo model). For the east-hypo model, the maximum amplitudes of the simulated horizontal ground motion in the Oita plain was three to four times as large as that on a rock site beside the plain. Especially in the bay area, the maximum ground motion reached 100cm/s and the pseudo velocity response spectra at period 6-8s were more than 400cm/s. On the other hand, the ground motion simulated by the west-hypo model was roughly one fifth smaller than that by the east-hypo model. It is also pointed out that in the east-hypo model simulation, the seismic waves generated by the two asperities near to the Oita plain are enlarged due to the directivity effect and amplified and prolonged by the sedimentary basin structure.

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. 2輯 (ISSN:00371114)

巻号頁・発行日

vol.49, no.1, pp.85-88, 1996-05-24

参考文献数

15

被引用文献数

3

著者

河野 俊夫 仁田 交市 松本 聡 堀内 茂木 岡田 知己 開原 貴美 長谷川 昭 堀 修一郎 海野 徳仁 鈴木 将之

出版者

日本地震学会

雑誌

地震. 2輯 (ISSN:00371114)

巻号頁・発行日

vol.46, no.2, pp.85-93, 1993-09-24

参考文献数

30

被引用文献数

8

著者

齊田 時太郎

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.6, no.6, pp.318-325_1, 1934-06-15 (Released:2010-03-09)

著者

三好 寿 牧野 清

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.33-43, 1972

---

The lowlands of southwestern islands of Okinawa are dotted with many blocks of coral which were quarried and conveyed from the reef on the floor of the sea, by the giant tsunami of April 24, 1771. We investigated the distribution of blocks in Ishigaki Island. We chose the third biggest block in this island, the approximate weight of which is 750 tons. It lies some 2.5 kilometers away from the nearest coast line, and its location reaches some 30 meters above sea level. We pierced a tunnel through the base of this huge block, which is the hardest to be imagined to have been conveyed by the tsunami, and demonstrated that this block takes no root. In the opinion of some persons, these blocks are the negro heads of the erosion type. But our tunnel crushed down this opposition. One is apt to feel that this capacity of the tsunami is rather fantastic in view of wave dynamics. But, for example, the giant wave observed in Lituya Bay (Alaska) in 1958, the energy of which was ascertained accurately, could have conveyed the supposed coral pillar whose cross section is some 27.3mm<SUP>2</SUP>, to the same position of the above-mentioned block, losing only 0.73% of its wave energy.<BR>Then we considered the action of the tsunami of 1771 upon the tied-island called Funakuy&acirc; in Ishigaki Island. We confirmed that it is traditionally said that the northern part of this island has never been isolated from the main part of the island.

著者

相田 勇

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.449-460, 1975

被引用文献数

3

---

On May 21, 1792, a gigantic collapse of Mt. Mayuyama in Shimabara Peninsula, Kyushu, occurred. Following this event, a severe tsunami of about 10 meters in height was generated by the landslide and attacked the coast of Ariake-kai, killing more than 14, 500 persons. Many historical documents tell us the phenomena of this tsunami in fair details, so that we attempted to reconstruct a numerical model of the tsunami consistent with the historical data. In the numerical computation, a finite difference method with a leap-frog system is adapted, and two kinds of source input are tried; one is the prescrived water mass transport normal to shore line and the other the vertical displacement of sea bottom. When the transport of 18, 000m³/min (current speed-20m/sec) per unit length of shore on the center line of landslide area is assumed to be continued during 2 to 4 min, the computed waves agree fairly well with the real tsunami behaviors, the height of tsunami in various places along the coast and the order of the maximum crest in the sequence of a wave train. Therefore, it seems probable that the extraordinary flow of water normal to the shore occurred by some physical mechanisms of the mountain collapse.<br>The energy of this tsunami is estimated to be about 5&times;10¹⁹erg, and this is about 1/100-1/1000 of the available potential energy of the slided material due to the collapse of the mountain. It is significant that the tsunami energy is several times larger than that of the 1968 Hyuganada Earthquake (<i>M</i>=7.5). The wave spreaded over a wide area and gave distructive damages to the coast more than 120km on both side of Ariake-kai.

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. 2輯 (ISSN:00371114)

巻号頁・発行日

vol.51, no.2, pp.203-210, 1998-10-15

参考文献数

19

被引用文献数

1

---

The generating frequency of the North-West American tsunamis is relatively lower than that of the South American region, but there are historical records of a large tsunami accompaning with the January 1700 earthquake (<i>M</i> 9) in the Cascadia subduction zone (SATAKE <i>et al.</i>, 1996). In the present paper, tsunami magnitudes on the Imamura-Iida scale, <i>m</i>, are investigated by using the diagram of wave-height attenuation with distance. The regional characteristics of tsunami magnitudes are discussed in relation to earthquake magnitudes, <i>M</i>_s, during the period from 1899 to 1997. The tsunami magnitudes in the South-East Alaska to Canada region are nearly normal compared to earthquakes with similar size in the other Pacific regions, and the 1899 Yakutat tsunami being <i>m</i>=3 is the largest. The magnitude values in the California region are mostly <i>m</i>=0 or less (amplitude: 50-100cm), but those of a few tsunamis vary by the faulting mechanism. For example, the magnitude value of the 1906 San Francisco tsunami accompaning with a strike-slip earthquake (<i>M</i>_s=8.3) is <i>m</i>=-4. On the contrary, that of the 1927 Lompoc tsunami caused by a high-angle thrust earthquake (<i>M</i>_s=7.0) is <i>m</i>=1, and this tsunami was observed in Hawaii and Japan. According to the epicenter distribution of the earthquakes (<i>M</i>_s&ge;6.5) since 1812, a seismic gap exists at the segment of 700km off the Washington to Oregon states. It should be considered a region of relatively high tsunami risk.

著者

弘瀬 冬樹 前田 憲二

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.70, pp.21-40, 2017-05-10 (Released:2017-09-07)

参考文献数

32

被引用文献数

1 1

---

Frequency-magnitude distributions are generally expressed by the Gutenberg-Richter (G-R) law. However, frequency-magnitude distributions are sometimes a convex-upward curve rather than a straight line, departing from the G-R law. An η value originally introduced by Utsu (1978) is an indicator that represents the degree of deviation from the G-R law. We investigate η values before and after six M7-9 class mainshocks off the Pacific coast of eastern Japan. The η values tend to become small (i.e., the distribution deviates from the G-R law) before the mainshocks, and then increase (i.e., recovering to the G-R law). Taking this characteristic into account, we suggest a simple and challenging earthquake forecast model based on η values. Probability gain of the optimized forecast model by a retrospective test becomes 2.24-3.03, and the alarm rate and the truth rate become 100% and 0.14-0.47%, respectively. According to the result of the forecast model applied to the latest seismicity, we should pay attention to seismicity off the coast southeast of Kanto district.

著者

斎藤 正徳

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.17, no.1, pp.40-55, 1964-03-25 (Released:2010-03-11)

参考文献数

57

著者

山口 林造

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.17, no.1, pp.28-39, 1964-03-25 (Released:2010-03-11)

参考文献数

66

著者

竹内 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.17, no.1, pp.24-27, 1964-03-25 (Released:2010-03-11)

参考文献数

33

著者

佐藤 泰夫

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.17, no.1, pp.14-23, 1964-03-25 (Released:2010-03-11)

参考文献数

37