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.47, no.2, pp.183-183, 1994-08-14 (Released:2010-03-11)

参考文献数

2

著者

岩田 孝仁 浜田 信生

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.39, no.4, pp.621-634, 1986-12-25 (Released:2010-03-11)

参考文献数

18

被引用文献数

1 1

---

In the present study, we have accumulated most complete seismological data and reinvestigated the seismicity associated with the 1944 Tonankai earthquake. Because of poor observation and social difficulty during the World War II, incompleteness and insufficiency in observational data resulted in rather obscure view about the actual process and mechanism of the earthquake. Number of aftershocks and their location accuracy reported by existing studies seem to be dissatisfactory for detailed discussion.We found some observational data that are still available but have not been used yet, then, we applied a modern hypocenter location method to the newly compiled data and succeeded in increasing the number of accurately located aftershocks more than twice. The followings are important findings of the study.The mainshock initiated from the bottom of the fault plane, in the south-west corner of the focal region. This feature is in accordance with the results of some previous studies. Most of aftershocks concentrated in the vicinity of the Shima spur, which extends south-east from the Shima peninsula to the Nankai trough. Temporal broadening of the aftershock region toward south-east along the spur is recognized and this trend seems to continue over 40 years until now. Distribution of aftershocks around Shionomisaki, the southern top of the Kii peninsula, may suggest some overlapping of the focal regions of the Tonankai and the 1946 Nankaido earthquake. Aftershock activity or induced seismicity is also recognized in the middle part of Shizuoka prefecture where some seismologists assume the focal region of a future interplate earthquake, so called Tokai earthquake. Seismicity around the southern Izu peninsula may represent an induced activity along one of the active faults which strikes southeast from the peninsula. Other induced seismic activity in inland area of central Honshu indicates a large extent of the effect of the interplate earthquake on the tectonic environment of the mentioned area. This study will contribute to gain better understanding of the process and mechanism of the Tonankai earthquake.

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.15, no.2, pp.143-145, 1962-06-30 (Released:2010-03-11)

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.26, no.2, pp.204-205, 1973-10-30 (Released:2010-03-11)

参考文献数

8

被引用文献数

1

著者

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.44, no.Supplement, pp.99-112, 1991-07-24 (Released:2010-03-11)

参考文献数

82

被引用文献数

1

---

Recent studies on tsunamis are reviewed. Theoretical studies on tsunami generation and propagation have been done both on coupled and decoupled systems of ocean and solid earth. Both approaches are proved to be equivalent. Hydrodynamic formulation, on the basis of decoupling model, is discussed in detail. Several models have been proposed for the mechanism of tsunami earthquakes that produce abnormally large tsunamis compared to seismic waves. After the 1983 Japan Sea tsunami, some progress has been made on tsunami research. Among them are re-examination of tide-gauge system, studies on free oscillation of the Japan Sea and newly developed inversion technique of tsunami waveforms to estimate complex fault motion. Large-scale realistic computation of tsunamis can be made very rapidly and has potential usage for tsunami warning system. These seismology-related problems are described.

著者

飯尾 能久 松本 聡 松島 健 植平 賢司 片尾 浩 大見 士朗 澁谷 拓郎 竹内 文朗 西上 欽也 廣瀬 一聖 加納 靖之 儘田 豊 宮澤 理稔 辰己 賢一 和田 博夫 河野 裕希 是永 将宏 上野 友岳 行竹 洋平 Bogdan ENESCU

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.58, no.4, pp.463-475, 2006-03-31 (Released:2010-03-11)

参考文献数

44

被引用文献数

1 2

---

The 2004 Mid Niigata Prefecture Earthquake (MJMA 6.8) occurred on 23 October 2004. The mainshock was followed by four aftershocks with MJMA≥6.0. This earthquake is located in the Niigata-Kobe Tectonic Zone in which large strain rates (>0.1ppm/y contraction) have been observed by GPS data. We deployed three temporary online seismic stations in the aftershock area. Combining data from the temporary stations and from permanent stations around the aftershock area, we determined aftershock locations, and estimated the structures and the stress change in and around the aftershock region. Based on these results, we suggested a generating process of the 2004 Mid Niigata Prefecture Earthquake supposing that a very weak region exists in the weak zone in the lower crust just beneath the seismogenic fault.

著者

加藤 祐三

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.3, pp.377-381, 1987-09-25 (Released:2010-03-11)

参考文献数

6

被引用文献数

2

---

In Ishigaki Island, the southern Ryukyu Islands, there are many blocks consist of coral limestone. These are considered to be thrown onto the island by Yaeyama Seismic Tsunami in 1771 and so called “tsunami-ishi (means tsunami-stone)”. Based on a distribution of these tsunami-ishi, a record, in archives, saying that the run-up height of the tsunami was 85 meters has been admitted. Or according to the maximum height of the distribution, an assertion that the run-up height is 55 meters has been made.There are two kinds of blocks for these tsunami-ishi. One is genuine tsunami-ishi which is evidently thrown on the island by the tsunami. The other consists of the Pleistocene Ryukyu Limestone block. It cannot be determined whether the existence of these blocks is a result of the tsunami, or not. These coral blocks can be distinguished from each other by its components, either aragonite or calcite. That is to say, when the coral of a block consists of aragonite, it should be a genuine tsunami-ishi. When calcite, it should be a Ryukyu Limestone block. Since the research, made by this method, found out that the maximum height of the distribution of the genuine tsunami-ishi was 25 meters, it is inferred that the run-up height was a little higher than 25 meters.In Miyara Bay of Ishigaki, there is also a block about 100 tons in weight clung by some small coral whose 14C-age corresponds with that of Yaeyama Seismic Tsunami. The 14C-age of this block itself is 2980BP. This suggests that, between at least 3000 years ago and 1771 of Yaeyama Seismic Tsunami, there was no such huge tsunami which could have thrown this large block at Miyara coast. Since, among the genuine tsunami-ishi, the 14C-age of coral of a block, distributing at the altitude of 25 meters, which is the highest altitude for this particular block, is 1810BP, this block is inferred to have been thrown by the tsunami and the value of a little higher than 25 meters is considered to indicate the maximum height of Yaeyama Seismic Tsunami.

著者

吉田 真吾 加藤 尚之

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.58, no.3, pp.231-246, 2005-12-25 (Released:2010-03-11)

参考文献数

44

被引用文献数

1

---

This paper reviews studies on the relation between the eventual earthquake size and its rupture nucleation size. Although a large number of studies have been made in order to find whether the seismic nucleation phase depends on the eventual earthquake size or not, this subject is still in controversy. Several recent papers have reported that the duration of the seismic nucleation phase scales with the final rupture size, and that the scaling relation can be explained by rupture nucleation models. These studies suggest that larger preslip occurs before a larger earthquake. On the contrary, other papers have reported that the seismic nucleation phase is independent of the earthquake size; earthquakes of all sizes initiate in a similar manner. Adding to these existing studies, we perform a numerical simulation of sliding behavior on a fault assuming two asperities of different sizes. The result shows that when the rupture of the small asperity triggers the rupture of the large asperity, short term preslip occurs at the small asperity, and the magnitude of the preslip does not depend on the eventual earthquake size. However, intermediate-term aseismic slip which occurs around the main asperity depends on the eventual earthquake size.

著者

久保寺 章 岡野 健之助

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.13, no.4, pp.210-218, 1960-12-25 (Released:2010-03-11)

参考文献数

5

---

The seismic waves due to the great nuclear explosions in the central Pacific Ocean (Bikini Atoll) in June and July 1958 were recorded by routine seismographs at the Abuyama Seismological Observatory of Kyoto University.The remarkable result was that we found a new kind of wave-group which has the following properties on the records of long-period seismograph. The wave in this group is of a period 9 to 1 minute and its propagation velocity is about 300m/s. The arrival time is about 3 hours later than that of seismic P-wave. These properties are similar to those of the microbarographic oscillations produced by the nuclear explosions, and the phenomena can hence be attributed to the effect of atmospheric pressure fluctuations upon the inertia mass of the seismograph.

著者

趙 志新 松村 一男 尾池 和夫 石川 有三

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.3, pp.383-396, 1987-09-25 (Released:2010-03-11)

参考文献数

23

被引用文献数

4 4

---

Mutual relations of seismicity in the long period in various regions from North China to Japan trench in East Asia have been analyzed. Time series of events were analyzed in various regions in North China, Korean Peninsula and Japan Island.The seismicity of each region was high in the period from 1550 to 1700. Then quiet period had been lasting until 1900. From 1900 the active period began again and have continued up to the present.Impulsive activities were found in the western part of North China and Japan Islalds in a short time range around 1830 during the quiet period. It seems that short period variations superpose on the long period variation. These short period variations in two regions also correlated to each other.Synchronous variations of seismicity in these regions are implicated in the formation of earthquake generating stress fields from North China to Japan trench under the common tectonic conditions. The release and the accumulation of stresses correspond to the active and quiet period of seismicity, respectively.Correlations among seismicities and stress fields from North China to Japan trench suggest that there is a transmission of the tectonic force from the subduction of the pacific plate along the Japan trench to North China through Korean Peninsula.

著者

八木原 寛 角田 寿喜 宮町 宏樹 後藤 和彦 平野 舟一郎 日野 亮太 金澤 敏彦 海宝 由佳 塩原 肇 渡邊 智毅 望月 将志 根本 泰雄 島村 英紀

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.2, pp.227-239, 1996-08-23 (Released:2010-03-11)

参考文献数

23

被引用文献数

1 1

---

We investigated seismic activity around Tokara Channel north off Amami Oshima, Nansei Syoto (Ryukyu) Islands of western Japan, using 12 ocean-bottom seismographs (OBS), as well as two temporal stations at Yaku Shima and Amami Oshima islands, operated from April 16 to May 10, 1992. One-dimensional velocity structure and station corrections were inverted from P and S times of 51 events provisionally well-located in the OBS network. We then relocated precisely 239 events in the studied region, using the inverted velocity structure and station corrections.Seismicity was highest in an area of about 10km×10km near the trench axis northeast off the OBS network: the largest event of MJMA 5.6 and other 40 events (probably aftershocks) were located at shallow depths. A mechanism solution of normal fault type with a T-axis of NW direction for the largest event was concordant with bending process of the Philippine sea plate. On the other hand, 18 events at depths of about 30km in a small area north of the OBS network were presumably due to interplate thrusting, because a composite mechanism solution for three events was of reverse fault type with a P-axis of ESE direction. A cluster of 17 events at depths from 10km to 25km was found in a southwest area of the network. These shallow events were probably crustal earthquakes within the Eurasian plate.We found an area of very low seismicity in the southeast of the network during the period studied. It is also identified at the nearly same location in the epicenter distribution from 1984 through 1991 obtained by Japanese Meteorological Agency (JMA) and possibly corresponds to the aftershock area of the 1911 Kikaijima Earthquake (M 8.0).Although we could not confirm any discernible alignments of shallow earthquakes along the Tokara Channel which is a notable tectonic line, the dipping angle of the intermediate-deep seismic zone changes discontinuously from about 65° on the north of the channel to about 40° on the south.

著者

小松 正直 竹中 博士 岡元 太郎 中村 武史

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.76, pp.17-30, 2023-05-24 (Released:2023-07-27)

参考文献数

57

---

In this study, we conduct First-motion Augmented Moment Tensor (FAMT) analysis to estimate the source parameters of small-to-moderate suboceanic earthquakes (MJMA 4.5-5.8) occurring off the Okinawa island, Japan, from October 2007 to April 2020. We calculate Green’s functions for a land-ocean unified 3D structure model that includes non-flat complicated land and seafloor topographies, the sediment layers, the oceanic plate and Moho interfaces obtained by compiling with recent seismic survey results. For the inversion, we use velocity waveform data in two period ranges of 4-40 s and 10-40 s and reproduce both the body and surface waves at K-NET and F-net stations. The results indicate that two of ten events are located in the oceanic mantle of the subducting Philippine Sea (PHS) slab, and eight ones are located in the oceanic crust of the PHS slab. The focal mechanisms of the former two events are primarily strike-slip and/or normal-fault type. The latter crustal events have mechanisms of reverse-fault type with the extension axis of NW-SE direction, which is consistent with the subducting direction of the slab. It is found that the depth difference between the JMA unified hypocenter catalog in travel time data and our estimated FAMT solution is large for events near the Ryukyu trench. Our results show that the offshore events in the trench side are located around the submarine active faults and are the same strike direction as the orientation of the faults.

著者

㓛刀 卓 青井 真 中村 洋光 鈴木 亘 森川 信之 藤原 広行

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.65, no.3, pp.223-230, 2013-01-31 (Released:2013-07-19)

参考文献数

7

被引用文献数

14 15

---

We present an improved implementation of the approximating filter for real-time seismic intensity calculations proposed in previous work. As earthquake early warning (EEW) systems become ever more widely used, the current method of computing a JMA (Japan Meteorological Agency) seismic intensity shows a serious problem since it introduces a time delay resulting from frequency domain filtering. In order to improve this method to permit real-time calculations suitable for EEW systems, we have proposed a real-time seismic intensity computed using an approximating filter in the time domain. For a simple computing system such as a strong-motion seismograph, it is straightforward to calculate the real-time seismic intensity because the approximating filter consists of only four first-order filters and one second-order filter. Based on testing using K-NET and KiK-net strong-motion seismographs, we have found that a strong-motion seismograph has enough computational capacity to undertake more sophisticated filtering. Here, we develop an approximating filter consisting of six second-order filters applied in the time domain for accurate real-time seismic intensity calculation. The relationship between the JMA seismic intensity and the real-time seismic intensity calculated using the improved approximating filter is examined using a large number of strong motion records. The results show that the differences between the JMA seismic intensities and the real-time seismic intensities are less than 0.1 for 99% of all records. Although the improved filter requires twice as much computation power as the previous approximating filter, it is suitable for EEW systems that require more accurate real-time calculations of seismic intensity.

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.40, no.3, pp.417-423, 1987-09-25 (Released:2010-03-11)

参考文献数

11

被引用文献数

2 2

---

The minute investigation of the spatial distribution of intermediate-depth earthquakes reveals that the deep earthquake zone beneath the Kyushu-Ryukyu region is dislocated transversely and changes its strike under the Tokara Channel.Left-lateral dislocations of the isobaths of intermediate-depth earthquakes amount to 70-80km and 30-40km at depths of 80km and 150km, respectively. The isobath of the depth of 200km, however, is scarcely dislocated. The change in strike of the deep earthquake zone comes up to about 30° there.The discontinuity of the zone appears to be related closely to the surface geology. The Tokara Channel represents the left-lateral geological fault offsetting by 80-100km the tectonic belts in the pre-Miocene basement rocks running parallel to the island arc. In this region, there are a few left-lateral faults including the Tokara Channel, which traverse the Ryukyu Islands and divide the pre-Miocene tectonic belts into segments of 200 to 400km in strike length. But the other transverse discontinuities of the deep earthquake zone corresponding to the surface geological structure can not be found from the present analyses.

著者

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.44, no.Supplement, pp.329-340, 1991-07-24 (Released:2010-03-11)

参考文献数

123

被引用文献数

1 1

---

Recently, telemetered microearthquake observation networks have been developed, and data acquisition and processing procedures have been automated in many networks, including automatic hypocenter determinations by using computers. As a result the detection capability and the accuracy of hypocenter determination of microearthquakes have been tremendously improved, which made a great advance in detailed microearthquake studies. We present a brief review on recent studies of seismicity based on microearthquake observations, focusing on spatial and temporal distributions of microearthquakes and their related problems.

著者

古田 俊夫 藤本 博巳 中西 正男 村上 英幸

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.233-241, 1990-06-24 (Released:2010-03-11)

参考文献数

5

---

Acoustic digital data telemetry makes it possible to retrieve the observed values on a surface ship at any time during long-term underwater measurement. Several sea trials have been carried out totest feasibility and reliability of the telemetry by means of acoustic pulses from an ocean bottom heat flow meter newly developed for long-term measurement. More than 90% of values retrieved by the acoustic telemetry is in good agreement with ones memorized in the bottom equipment and recovered later. Bit length of each acoustic pulse for this data telemetry can be selected from 100msec to 10msec in accordance with the ambient acoustic noiselevel. Under normal sea states, 20msec is sufficient length of a pulse for the data retrieval from a depth of 6, 000 meters.

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.51, no.2, pp.203-210, 1998-10-15 (Released:2010-03-11)

参考文献数

21

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 (M 9) in the Cascadia subduction zone (SATAKE et al., 1996). In the present paper, tsunami magnitudes on the Imamura-Iida scale, m, 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, Ms, 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 m=3 is the largest. The magnitude values in the California region are mostly m=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 (Ms=8.3) is m=-4. On the contrary, that of the 1927 Lompoc tsunami caused by a high-angle thrust earthquake (Ms=7.0) is m=1, and this tsunami was observed in Hawaii and Japan. According to the epicenter distribution of the earthquakes (Ms≥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

小泉 尚嗣 木下 千裕

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.125-134, 2017-07-10 (Released:2017-09-07)

参考文献数

25

---

The Dogo hot spring, situated in Matsuyama City, Ehime Prefecture, Japan, is one of the oldest and most famous hot springs in Japan. The well water level or discharge at the spring often decreased coseismically and increased postseismically related to the past Nankai earthquakes. We analyzed well water level data recorded at the spring immediately after the 1946 Nankai earthquake and over the period from 1985 to 2015. From this analysis, we have got five postseismic well water level increases related to the earthquakes whose seismic intensities were four or greater at Matsuyama city in JMA scale. The pattern of the five postseismic increases is very similar and shows a tendency of exponential convergence. We found that these postseismic increases can be explained by a basic equation of groundwater motion, which is a kind of diffusion equation. We also tried to detect the change in the diffusion coefficient or hydraulic diffusivity. However we did not detect it.

著者

斎藤 正徳 阿部 豊

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.2, pp.237-245, 1984-06-25 (Released:2010-03-11)

参考文献数

8

被引用文献数

8 9

---

The viscous relaxation spectra and the marginal stability curves of Rayleigh-Bénard convection in a transversely isotropic fluid were computed. An incompressible, transversely isotropic fluid is expressed in terms of two material constants, L and δ. L is the viscosity pertinent to the shear in the horizontal plane and δ is the anisotrpy factor. δ is likely to be very large in the mantle if thin less viscous (molten) layers are aligned in the horizontal plane. At large δ the relaxation spectra become nearly constant over a wide range of wavenumber and its magnitude is determined essentially by the product L·δ. The flattness is consistent to the observed relaxation spectra. A similar effect is found in the Rayleigh-Bénard convection; the marginal stability curve flattens out to small wavenumber at large δ. This implies a possibility of thin convection cells in the earth's mantle.

著者

武村 俊介

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.71, pp.13-41, 2018 (Released:2018-06-26)

参考文献数

211