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 17

---

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

福富 孝治

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.12, no.5, pp.195-207, 1940-05-25 (Released:2010-11-17)

参考文献数

6

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

著者

武者 金吉

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.11, no.7, pp.337-343, 1939-07-25 (Released:2010-03-09)

参考文献数

9

著者

小笠原 宏 川方 裕則 石井 紘 中谷 正生 矢部 康男 飯尾 能久 南アフリカ金鉱山における半制御地震発生実験国際共同研究グループ

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.563-573, 2009-07-31 (Released:2013-11-21)

参考文献数

54

被引用文献数

2 3

---

Experimental sites with potential earthquakes up to M ∼ 3 in coming few years are known beforehand from mining schedule at 2-3 km depths in South African gold mines, which allows us to deploy various borehole instruments including Ishii strainmeters, geophones, accelerometers and AE sensors. Deployment of these wide-dynamic-range and high-resolution observations in the past 15 years has led to many findings about the earthquake rupture and its preparation stage. High-sampling seismograms obtained at close proximity of M > 1 earthquakes have demonstrated similarities of these earthquakes to natural, greater earthquakes in many aspects, including stress drop, energy efficiency, and complexity of rupture propagation. Some of larger mine earthquakes are preceded by perceivable abnormal seismicity. However, no immediate precursors for earthquakes with M ∼ 2 were observed by our high-resolution strain and AE sensors installed within the dimension of mainshock rupture. In contrast, aseismic strain-step events that we had recently discovered were sometimes preceded by further slower forerunners. Ongoing projects bring in novel technologies such as field-scale AE monitoring and fast-response strainmeters, and novel targets including mines being flooded for closing operation.

著者

橋本 学 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.41, no.1, pp.29-38, 1988-03-25 (Released:2010-03-11)

参考文献数

22

被引用文献数

4 4

---

Displacements and strains during the recent 80 years in Hokkaido are investigated by the analysis of triangulation or trilateration data. According to the distribution of displacements and strains, Hokkaido can be separated into three blocks, eastern, middle and southwestern Hokkaido.In eastern Hokkaido, northwestward displacements and NW-SE contractions are dominant before the 1973 Nemuro-Oki earthquake, while seaward displacements and EW extensions are detected after the event. Summing up them, westward displacements are left, which suggests westward sliding of the outer Kurile arc along the volcanic front and colliding at the Obihiro Tectonic Line [TADA and KIMURA (1987)].The Ishikari Low Land, which is considered to be a relic trench, may be the boundary between middle and southwestern Hokkaido along which E-W contractions are prevailing. This observation suggests that northern Honshu would not belong to the North American or the Okhotsk plate.Displacements associated with four major earthquakes which occurred during the period between the first and the last surveys are computed. Results show that the 1940 Shakotan-Oki earthquake may not give much influence on Hokkaido. Theoretical displacements computed by models for the 1952 Tokachi-Oki (M8.1) and 1968 Tokachi-Oki (M7.9) earthquakes are inconsistent with the observation, which may require re-analyses of data. The model for the 1973 Nemuro-Oki earthquake can predict the observed displacements qualitatively. The observed displacements are greater than the computed ones by a factor of two or three, which means that old triangulation surveys might suffer from scale errors.

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.1, pp.47-53, 1976-03-10 (Released:2010-03-11)

参考文献数

10

被引用文献数

1 1

---

The subcrustal structure beneath the Kanto plain was studied by geological and gravity data. Bouguer gravity anomalies were corrected by the thicknesses of the sedimentaly layers, and then Bouguer gravity anomalies were reduced to the basement. This correction coresponds to the Bouguer's correction.The reduced gravity anomaly represents the structure under the basement if the thicknesses of the sedimentaly layers are correct. But the depthes of the basements (the thicknesses of the sedimentaly layers) are not always so correctly measured that the reduced gravity anomalies will represent the structure beneath the basement and the structure of the basement as well.The reduced gravity anomaly map shows that the high gravity belt, or the anomalous gravity gradiant zone exists along the north side of the Tama-gawa river and the low garvity zone exists north side of the high gravity belt around the Sayama hill.These gravity anomalies also show that the geological tectonic line (the fault) lies along the north side of the Tama-gawa river with the drop in its north-east side near the Sayama hill. This fault passes the western part of Tokyo from north-west to south-east.

著者

加藤 昭七郎

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.10, no.3-4, pp.123-140, 1957-12-25 (Released:2010-03-11)

参考文献数

10

---

Assuming the fluid motion of vT1°-type (expression (3.1) in §3), we have studied here the time characteristics of self-exciting fluid dynamos. As a result of theoretical calculations, it has been found that three magnetic fields expressed by three surface spherical harmonics Ymn-1, Ymn and Ymn+1((n, m)-harmonics in §3) can coexist independently of other magnetic fields. These three magnetic fields oscillate concurrently in intensity quasi-periodically with time, the frequency being proportional to order m, fluid velocity and depth of the fluid layer. The westward drift of the earth's magnetic field and also the reversal of the magnetic field of the sun may be well explained by the above results. The periodical dynamo presented here may also be appropriate as a model for magnetic variable stars.

著者

熊谷 博之 中野 優

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.379-390, 2009-07-31 (Released:2013-11-21)

参考文献数

85

被引用文献数

1

---

We review recent advances in quantification of the sources of volcano-seismic signals. Since the 1990s, there have been remarkable advances in quantitative understanding of the sources of volcano-seismic signals. These were made by integrated contributions from observation, analysis, and modeling studies in volcano seismology. We focus on the following topics in this review paper: Broadband seismic observations on active volcanoes, waveform inversions of volcano-seismic signals, and source models based on resonances of a fluid-filled crack, bubble dynamics, and repeated fracture and healing of magma. Broadband seismic observations revealed the general existence of very-long-period seismic signals with oscillation periods longer than a few seconds beneath active volcanoes. Development of waveform inversion methods enabled us to estimate source mechanisms of volcano-seismic signals, which indicate that crack geometry is the most common in volcano-seismic sources. Source models have been successfully used to interpret dynamic interactions between volcanic fluids and the surrounding solid rock. Quantitative studies of volcano seismology are now reaching a mature stage, and links with geological and geochemical studies will be important future directions to achieve a better understanding of magmatic and hydrothermal processes beneath active volcanoes.

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.25, no.3, pp.263-264, 1972-12-30 (Released:2010-03-11)

参考文献数

6

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.48, no.2, pp.271-280, 1995-08-25 (Released:2010-03-11)

参考文献数

14

---

Previous equation for the tsunami-magnitude scale after Abe (1981) has been re-examined using a more general form: M10=logA+a log Δ+b, where Mto is tsunami magnitude, A is the maximum double amplitude of tsunami as recorded on a tide gage, Δ is the shortest distance along oceanic path from the earthquake epicenter to a tide station, and a and b are constants. ABE (1981) used a=1 and b=5.55 in his determination of tsunami magnitude. This paper demonstrates, using more extensive sets of tide records, that the constants, a and b, vary regionally. For instance, a=0.86 and b=5.96 for tsunamis along the Pacific coasts in and around Japan, and a=0.52 and b=6.56 for tsunamis in the Japan Sea. These constants vary even in more regional scales and may depend on the submarine topography along a tsunami path. Renewed equations should be used for the determination of tsunami magnitude.