著者

古賀 祥子 伊藤 喜宏 日野 亮太 篠原 雅尚 海野 徳仁

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.2, pp.75-90, 2012-01-25 (Released:2012-02-20)

参考文献数

32

被引用文献数

2 4

---

A double-planed shallow seismic zone has been found in the northeastern Japan forearc region. However, the characterizations of the focal mechanisms of earthquakes in this zone, especially the lower plane events, cannot be carried out adequately due to low seismicity and poor station coverage on the focal sphere of the onshore P-wave polarity data. In this study, we determine the focal depth using the sP depth phase and the focal mechanisms using the P-wave initial motions observed by the ocean bottom cabled seismic stations and temporary autonomous ocean bottom seismic networks off Miyagi, as well as the onshore seismic networks. Seven focal mechanism solutions of events were precisely determined. Using the classification based on the dip angles of the T, B and P axes, we classified 21 weakly constrained focal mechanisms of other events having poor station coverage. All the determined solutions were of the thrust-faulting type regardless of the focal depth. The offshore observations helped considerably in constraining the focal mechanisms of these far-offshore earthquakes, especially their rake angles. Although previous studies had reported that the focal mechanisms of the upper and lower plane events show predominantly normal and reverse faulting respectively, our result showed that the thrust events in the upper plane seem to occur on the plate boundary. We found that the focal mechanisms change from normal faulting in the upper plane to reverse faulting in the lower plane at a depth of 15km from the plate boundary, possibly defining the depth of the neutral plane in the northeastern Japan forearc region included in the source area of the 1933 Mw8.4 Sanriku earthquake. The western edge of the normal faulting events along the upper plane is located about 70km inward from the trench axis. These results suggest that the earthquake-generating stress field in the double-planed shallow and deep seismic zone in the northeastern Japan arc can be explained by the bending-unbending model of the subducting Pacific plate.

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.55, no.3, pp.311-316, 2002-12-15 (Released:2010-03-09)

参考文献数

19

被引用文献数

1 2

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.51, no.3, pp.335-338, 1998-12-25 (Released:2010-03-11)

参考文献数

19

被引用文献数

2

著者

飯尾 能久 松澤 暢 吉田 真吾 加藤 照之 平田 直

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.56, no.2, pp.213-229, 2003-09-16 (Released:2010-03-11)

参考文献数

97

被引用文献数

1

---

We review recent studies on spatial distribution of asperities, and space-time variations of aseismic slips deduced from analyses of strong ground motions, displacement rates, continuous crustal deformations, and repeated microearthquakes in the Sanriku-oki region along the Japan trench. These various analyses suggest a possible scenario about occurrence of large earthquakes; asperities, which are defined as areas of large slips at earthquakes, repeatedly break when the stresses at asperities are loaded and reach to their strengths by aseismic slips occurring in the surrounding regions. If this scenario is the case and we estimate the strength, extent of asperities, and space-time variations of aseismic slips around the asperities, we will be able to forecast occurrence of large earthquakes to some extent. Moreover, we will be able to simulate the whole subduction process including seismic cycles along a subducting plate boundary if we find a conclusive constitutive law of frictional slip and succeed in estimating detailed distribution of the frictional parameters on the plate boundary. Although loading and generation mechanisms of intraplate earthquakes might not be the same as the interplate ones, the slow slips along the fault surface must play an important role for their generation.

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.27, no.4, pp.321-337, 1974-12-30 (Released:2010-03-11)

参考文献数

51

被引用文献数

6

---

Source areas of the tsunamis generated in northeast Japan since 1896 are compiled on a bathymetric chart (Newly estimated: 14; Reanalyses: 14). Sources of large tsunamis lie on the steep continental slope off the Sanriku coast. Most of small tsunami sources are located in the sea shallower than the depth of 2000m. Source dimensions are closely related with earthquake magnitude; the Utsu formula for the relation between the earthquake magnitude and aftershock area can be applied well for the tsunami source area. Generally speaking, the magnitudes of tsunami correspond to earthquake magnitude. However, a few tsunamis generated in the vicinities of the west Aomori and Miyagi regions are especially small in comparison with those at other regions.Judging from the initial motion on tsunami records, most of tsunamis off the Sanriku coast seem to be generated by the reverse fault type earthquake. The sense, up or down, of the initial motion of the 1896 Sanriku tsunami is opposite to that of the 1933 tsunami which is caused by a normal fault earthquake. This suggests that the 1896 tsunami was generated by the reverse fault earthquake. Source dimension of the 1933 tsunami is newly revised and found to be about 300km. This area is smaller than the former estimations, because arrival times at the tide stations of Hokkaido were read too early by misunderstanding a noise as the first motion.

著者

尾池 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.39, no.3, pp.475-477, 1986-09-25 (Released:2010-03-11)

著者

末次 大輔 塩原 肇

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.73, pp.37-63, 2020-06-05 (Released:2020-07-31)

参考文献数

137

---

Broadband ocean bottom seismometers (BBOBSs) have been developed since 1990s and put into practice to explore the structure of the Earth’s interior beneath oceanic regions, e.g., mid-oceanic ridges, subduction zones, hotspots, and oceanic lithosphere-asthenosphere boundary. The BBOBSs have been used to investigate earthquake source process including slow earthquakes and oceanographical phenomena. The best way for the broadband seismic observation in the oceanic region seems that the borehole seismic observatory connected with the ocean floor cable, which is realized in several networks deployed close to the coast but it is rare even now. For scientific targets far away from the coast, we still need to develop and operate the autonomous system of BBOBS with better S/N for a temporary observation for focused scientific targets. In this review article, focusing mainly on achievements made in Japan, we describe a history of the development of BBOBS and some related instruments, scientific results based on observations with the BBOBSs, and future direction of broadband ocean bottom seismology.

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.4, no.4, pp.210-219, 1932-04-15 (Released:2010-11-17)

参考文献数

4

著者

江本 賢太郎 汐見 勝彦 那須 健一

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.72, pp.35-41, 2019-06-05 (Released:2019-08-03)

参考文献数

23

---

Spatial distribution of seismicity has hitherto been visualized on two-dimensional maps and vertical cross-sections along certain lines so far. Owing to the advances in technology, we have developed a mobile application for iPhone and iPad devices, which can display the seismicity of Japan in three-dimensional (3D) view. Each hypocenter is plotted as a 3D spherical object whose color and size represented its depth and magnitude, respectively. The geometry of the Philippine Sea Plate and the Pacific Plate can be plotted as 3D polygons with the hypocenters, simultaneously. In addition to those plate boundaries, the topography of Japan and the ocean bathymetry around it are also plotted as a 3D polygon. The 3D image of the hypocenters and plate geometries helps users to perceive intuitively the spatial distribution of earthquakes such as that many earthquakes occur along the subducting plates. Moreover, the spatiotemporal distribution of seismicity can be seen by the time-lapse animation of hypocenters. The hypocenter catalog can be downloaded through the Internet by using the account of NIED MOWLAS. More than one month’s earthquakes (18,000 events) can be displayed smoothly.

著者

中原 恒

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.68, no.4, pp.75-82, 2015-11-10 (Released:2016-01-16)

参考文献数

51

被引用文献数

1 3

著者

松澤 暢

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.347-355, 2009-07-31 (Released:2013-11-21)

参考文献数

53

被引用文献数

3 3

---

Discovery of small repeating earthquakes and development of rate- and state-dependent friction laws have brought a modification of the asperity model that was originally proposed by Kanamori’s group. In the modified asperity model, ‘asperity’ is a synonym of ‘seismic patch’on the plate boundary. The area other than asperities on the boundary is supposed to slip aseismically. Careful analyses of interplate large earthquakes also support the model. This model gives a basis of current long-term earthquake prediction. Further detailed analyses of the relation between the pore pressure and rupture process and the interaction among the asperities and aseismic areas are mandatory for the improvement in the accuracy of the prediction.

著者

吉田 則夫 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.55, no.2, pp.207-216, 2002-10-31 (Released:2010-11-17)

参考文献数

36

被引用文献数

3

---

In the final stages of the Matsushiro earthquake swarm (August 1965-October 1967), a large volume of groundwater was generated that continues to flow as of this writing. We studied the spring water origin by measuring oxygen/hydrogen isotope ratios and concentrations of Na+ and Cl, the main dissolved ions. We took water samples from June 1999 to October 2000. Data plots for δ18O vs. δD are distributed along a well determined linear regression line having an endpoint, i.e., river water, at the ordinary value of rainwater. The regression line can be extrapolated toward estimated δ18O and δD of “andesitic magmatic water” originating from magma in subduction zones. This implies that the Matsushiro groundwater can be regarded simply as a mixture of 2 fluids, i.e., surface water and andesitic magmatic water. We obtained the carbon isotope ratio of CO2, the main component of free gas in spring water. δ13C ranges from -7.1‰ to -3.1‰, suggesting that the source of CO2 is also magmatic. The ratio 3He/4He shows that He in the free gas is from the mantle or magma. These 3 pieces of evidence - (1) δ18O and δD values, (2) δ13C of CO2, and (3) 3He/4He - suggest that the origin of Matsushiro water is magmatic. Considering the presence of an electric conductive layer and seismic reflective layers 15 km beneath the Matsushiro area, we presume that this andesitic magmatic water accumulates as a thin layer at this depth. An impermeable sheet presumably lying just above the water layer was formed by precipitates from magmatic water.We present the following model of the relation between groundwater and earthquakes : When the impermeable sheet broke and high-pressure water with CO2 rose into the upper crust, the crust was weakened, causing the Matsushiro earthquake.

著者

宮本 貞夫

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.7, no.2, pp.137-138, 1954-09-05 (Released:2010-03-11)

著者

金折 裕司 川上 紳一

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.49, no.1, pp.125-139, 1996-05-24 (Released:2010-03-11)

参考文献数

57

被引用文献数

2 3

---

Several boundaries of tectonic blocks can be defined as the lines linking large-scale active faults in Southwest Japan. Using available data concerning geology and geophysics, tectonic features of the block boundaries have been briefly reviewed. These features imply that Southwest Japan is separated into a few microplates. Based on the microplate model of Southwest Japan, sequential generation of large earthquakes including the 1995 M7.2 Hyogo-ken-nanbu earthquake can be interpreted. The Hyogo-ken-nanbu earthquake occurred in the middle of the 100-km long Takatsuki-Rokko-Awaji tectonic line (TATL). The aftershock distribution and the surface ruptures suggest that the main shock is caused by a 40-km long rupture of the central part of the TAIL. Thirty-kilometer long eastern and western parts of the TATL remain unruptured. The average moment-release rate of the 40-km central part of the TATL can be estimated from the slip-rate of constituent active faults. The magnitude of an earthquake generated at the central part can be predicted from the seismic moment, which is calculated from the moment-release rate and the elapsed time since the 1596 Keicho-Fushimi earthquake. The calculated magnitude of 6.8 to 7.2 is consistent with the actual magnitude of the Hyogo-ken-nanbu earthquake. If the eastern and western parts unruptured have the same slip-rate as that of the central part, the accumulated moments after the previous event amount to the earthquakes with a magnitude of 6.7 to 7.1. A two-meter right-lateral slip along the Nojima fault, which constitutes western-central part of the TATL, occurred at the time of the Hyogo-ken-nanbu earthquake. This slip may help a southward migration of the Kinki-Outer mircoplate. The movement may reduce normal stresses along the Median Tectonic Line and may increase stress concentration along the Nankai trough. The kinematics of the microplate and sequential generation of large earthquakes along the microplate boundaries suggest a high probability of generating an offshore earthquake along the Nankai trough in a period ranging from 2003 to 2040 A. D.

著者

堀 貞喜 堀内 茂木 石田 瑞穂 大井 昌弘

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.395-405, 1999-12-25 (Released:2010-03-11)

参考文献数

26

被引用文献数

1 1

---

Recent advances in broadband seismic observation enable us to analyze high quality waveform data just after the earthquake occurrence. An automated system for rapid determination of earthquake mechanisms for local events occurring beneath central Japan is developed with this point as background. When an earthquake occurs, its hypocentral parameters are determined automatically in several tens of seconds. In a case when an event occurring in a given area has a magnitude larger than a certain value, its source process is automatically analyzed by the use of a broadband waveform inversion technique. Considering the importance to shorten the computer process time to obtain the result, we calculate the Green's functions immediately after hypocentral parameters are calculated and when waveform data to be used in the inversion are being retrieved. The data of the Earth's response parameters, which are used in the calculation of the Green's functions, are stored on the hard disk so as to reduce the total lapse time. As a result, the CMT solution and source time function can be obtained in a few minutes after the earthquake occurrence. Inadequacy of theoretical waveform calculated by the 1-D Earth's model is corrected by introduction of station corrections to the observed arrival time and overparameterization to the source time function, where a number of double couple small sub-events are located in a certain time range. The CMT solution is represented by superimpose of moment tensors of small sub-events with very short duration. All the sub-events are assumed to occur at the same location (i. e., at the hypocenter) but to have different onset times. The source time function is also estimated from the temporal distribution of the sub-events. To evaluate the reliability of the results obtained from the present study, we compare them with the following two data sets: i) focal mechanism solutions determined by P first motion analysis, and ii) CMT solutions obtained from the other method for the same events. Our results are basically consistent with these two sets of mechanism solutions. However the agreement of the solutions is obviously better among the CMT solutions. Possible explanation for the difference between CMT and focal mechanism solutions is that the latter may be inaccurate because of insufficient push and pull first motion data, or that the total rupture may occur along the fault different from the initial rupture.

著者

友田 好文 藤本 博巳 松本 剛 河野 芳輝

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.2, pp.293-301, 1982-06-25 (Released:2010-03-11)

参考文献数

16

---

R. G. A. (Residual Gravity Anomaly) was calculated along a section across the Hawaiian Ridge near Oahu Island by use of both the gravity data and the crustal velocity structure obtained by the explosion seismology. Anomalies of lithospheric thickness in this region were estimated from the result of the calculation of R. G. A. It is concluded that the thickness of lithosphere beneath the island is about 20k mthinner than that beneath the surrounding area as expected from the lithospheric thinning model.The values of R. G. A. in the Emperor Seamount Chain are smaller than those in the Hawaiian Region obtained in this work, so the thinner lithosphere beneath the seamount approaches the normal state with increasing the age of the seamount in the Hawaiian-Emperor Seamount Chain. This agrees with the lithospheric thickening model.

著者

田中館 秀三

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.1, pp.16-26_2, 1939-01-25 (Released:2010-03-09)

参考文献数

6

被引用文献数

1

著者

芝崎 文一郎

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.61, no.Supplement, pp.415-423, 2009-07-31 (Released:2013-11-21)

参考文献数

51

---

Recent high-resolution observations of crustal movements have revealed the occurrence of slow slip events (SSEs) along the deep parts of subduction interfaces. This report reviews the possible models for SSEs using rate- and state-dependent friction laws. SSEs can be modeled under the condition close to the stability transition. The triggered SSEs can be modeled considering a conditionally unstable cell. The self-triggered SSEs can be reproduced in a region that is unstable but close to being stable. In this case, the ranges of the constitutive law parameters for reproducing SSEs are limited. Further, SSEs can also be modeled by considering the frictional property of an unstable-stable transition zone that exhibits velocity weakening at low slip velocity and velocity strengthening at high slip velocity; this model is proposed on the basis of the results obtained in an experiment using halite around an unstable-stable transition zone. By considering this frictional property, Shibazaki and Shimamoto have reproduced short-term SSEs that are similar to the observed SSEs. This friction law needs to be verified experimentally under conditions that are relevant to the fault zones of SSEs. It is theoretically expected that for slip failure processes the propagation velocity is proportional to the slip velocity. This relationship appears to hold for observed SSEs. Therefore, SSEs can be regarded as slip failure processes occurring at deep subduction plate interfaces.

著者

永田 武

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.9, pp.447-456, 1936-09-15 (Released:2010-03-09)

参考文献数

5

著者

尾形 良彦

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.appendix, pp.115-127, 1998-03-31 (Released:2010-11-17)

参考文献数

64

---

The anomaly in focus is relative quiescence which is defined as a significant decrease of earthquake activity compared with the predicted occurrence rate by the estimated statistical model for the standard seismicity of the region: we use a point-process model called Epidemic Type Aftershock-Sequences (ETAS) model. Regardless of the seismicity level, the relative quiescence can take place. Size of such quiescence is seen in cumulative and M-T diagrams of transformed occurrence times by using the estimated ETAS model. By this method, we recognized significant, relatively quiet stages in shallow seismicity over M 5 class in a very wide area preceding all studied great earthquakes of M 8 class in and around Japan and also those of M 9 class in the world. However, we saw no relative quiescence for about 20 years up to 1990 in the wide areas which include the Tokai and Boso gaps [OGATA (1992)]. On the other hand, a few authors recently showed a very significant quiescence for the last 20 years since early or mid 1970's in the seismicity of certain areas in or around Tokai region. However, it turns out that these quiescence are seeming ones owing to magnitude shifts which took place during 1975?76. The magnitudes below MJ5.0 are substantially underestimated after the period. This shift is found and estimated by a statistical comparison of magnitudes between the JMA and USGS catalogs. Nevertheless, the recent seismicity with level of MJ≥5.5 in a very wide region including central and western Japan shows a significant relative quiescence since 1992, which may be related to the 1995 Kobe Earthquake of MJ7.2 but seems to be further extended to late 1996 when many M 6 class events successively occurred about the boundaries of the quiet region within a half year span.