著者

山内 常生 山田 守 奥田 隆

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.3, pp.301-310, 1981-10-25 (Released:2010-03-11)

参考文献数

16

被引用文献数

1 1

---

Precursory abnormal strain responses associated with rainfall are discussed in the present paper. The data analized are the strains observed at the Mikawa Crustal Movement Observatory (Toyohashi City, central Japan) for the period from January 1973 to April 1980. Each extensometer at the observatory is equipped with two or three sensors for the detection of irregularity in strain. Usually the observation gallery deforms uniformly after a rainfall, because the ground strain responses observed by the sensors attached on the same quartz pipe show nearly the same variation. We can calculate accurately these strain responses by a tank model from the precipitation at the observatory, but sometimes remarkable disagreements between the ground strains caused by rainfalls and the calculated values expected from the model are clearly seen before and after the occurrence of nearby earthquakes. Irregular deformations at the observation site are also observed. These abnormal strain responses to rainfall are observed for 18 earthquakes during the period from January 1973 to December 1979. Distribution of earthquakes which were accompanied by these precursory abnormal strain responses are restricted in the block whose boundary is characterized by the distribution of microearthquakes.

著者

佐藤 春夫 立川 真理子 大久保 正

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.197-205, 1984-06-25 (Released:2010-03-11)

参考文献数

15

被引用文献数

2 2

---

Preceding the eastern Yamanashi earthquake of magnitude 6.0, an anomalous tilt change up to 0.4 micro-radian was detected by the borehole-type tiltmeter at the Enzan station locating 31km north-west of the epicenter. The anomaly began 18 days preceding the earthquake and continued 10 days. The tiltmeter was installed at the bottom of the well of 89m depth. The resolution is 0.006μ radian and the long-term stability is better than a few μ radian per year. This tiltmeter had recorded similar tilt changes of the order of 0.4μ radian twice since it was installed in 1979. Both the changes had been caused by a large amount of precipitation accompanied by typhoons. During these 10 days, however, the maximum daily precipitation was 20mm, temperature change was smaller than 0.05°C at the bottom of the well, and there was no construction near the station. Therefore, we may interpret this anomalous tilt change as a precursor of the earthquake. The station is located in the fracture zone associated with the active fault, the Daibosatsurei-nishigawa fault; core samples obtained from the well were fractured and their P wave velocity was extremely low. The direction of the anomalous tilt vector change is nearly orthogonal to the strike of this active fault. This suggests that the observed upheaval of the epicentral block is the consequence of the hinge movement at the fault.

著者

岡田 真介 小松原 琢 中澤 努 中村 洋介 坂田 健太郎 納谷 友規

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.4, pp.257-264, 2012-06-25 (Released:2012-08-08)

参考文献数

11

被引用文献数

1 1

著者

渡辺 晃

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.3, pp.189-200, 1971 (Released:2010-03-11)

参考文献数

12

被引用文献数

22 46

---

Several formulas to determine the magnitudes of earthquakes with shallow foci from amplitude and focal distance in the regional range up to about 1, 000km, were newly derived by using the data observed at the Abuyama Seismological Observatory and its array stations, and compared in the cases from displacement and velocity seismograms.The patterns of maximum amplitudes versus focal distances show that the manner of decay of the displacement amplitude is practically similar to that of velocity amplitude in the distance range up to 200km, but markedly different in the range over 200km, because the phase of the seismic wave corresponding to the maximum amplitude varies from the body wave to the surface wave at the focal distance around 200km and the long period surface wave is sharply cut off with the steep slope of the frequency response curve of the velocity seismograph.The amplitude-distance curves at the close distance range up to about 40km, however, are folded in the case of displacement amplitude. This phenomenon may arise from the effect of exitation of refracted or reflected, or both phases having longer periods, resulting in an increase of about 0.3 in the magnitude value. Taking no account of these slight folds, the decay of the maximum amplitude is supposed to be nearly uniform throughout the distance range concerned. Thus, the decay factor, including the geometrical spreading, is estimated as r-1.73, which is just the same as in the Tsuboi's (1954) formula.The periods corresponding to the maximum amplitude were found to increase according to the earthquake sizes alone, when the same type of phase was traced. On the basis of this finding, an attempt was made to infer the relation between the source factor of displacement spectral density and the magnitude.

著者

中島 淳一 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.61, no.Supplement, pp.177-186, 2009-07-31 (Released:2013-11-21)

参考文献数

65

---

Since late 1990’s, a dense nationwide seismograph network has been constructed in the Japanese Islands with an average station separation of ∼ 20 km, which has produced the highest quality data in the world and contributed to enhance the understanding of seismotectonics and volcanotectonics there. Travel-time tomography using such high-quality data has provided two important constraints on water-transportation paths in subduction zones. One is the evidence for hydrous minerals in and immediately above the slab. The hydrated oceanic crust is imaged as a low-velocity layer to a depth of 40 km for the Philippine Sea slab and 70-130 km for the Pacific slab. Another low-velocity layer is revealed immediately above the Pacific slab down to a depth of ∼ 110 km, which might correspond to a hydrous layer through which water is carried to deeper depths. The other is seismological imaging of mantle upwelling. Mantle return flows induced by the subduction of the Pacific and Philippine Sea slabs are imaged in Tohoku and Kyushu, respectively, whereas that probably generated by the subduction of both the Pacific and Philippine Sea slabs is apparent in central Japan. A large upwelling in the upper mantle revealed in the Chugoku district might be the origin of Quaternary volcanism there.

著者

岩田 貴樹 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.51, no.1, pp.51-59, 1998-07-03 (Released:2010-03-11)

参考文献数

29

被引用文献数

1

---

We investigate the correlation between the occurrence of earthquake and the earth tide by analyzing the tail of the Matsushiro earthquake swarm that is recorded by the Matsushiro Seismic Array System during the period of November 1984 to December 1994. The seismic activity of the tail exhibits many bursts of earthquakes. We remove the bursts, because they affect our aim to investigate whether the correlation exists or not. We use the tidal strain data recorded by EW- and NS-component extensometers located in Matsushiro Seismological Observatory, Japan Meteorological Agency. We apply Schuster's test to the Matsushiro earthquake swarm. The hypothesis that the earthquakes in the swarm take place randomly is tested and is rejected for the EW-component. The earthquakes tend to occur when the tidal strain of the EW-component is in a compressional state. This state is consistent with the stress field at Matsushiro obtained by using focal mechanisms or in situ stress measurements.We also investigate the spatial variation of the correlation. A significant correlation is seen in the northwestern part of Matsushiro. The largest earthquake with magnitude of 5.2 occurred on 30 December 1986 near the region. We further investigate the temporal variation of the correlation in this region. The correlation becomes high right after the occurrence of the largest earthquake, whereas the correlation is low before the occurrence of it. This suggests that the strain changes caused by the largest earthquake make the correlation high in this region.

著者

村上 ひとみ 鏡味 洋史

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.44, no.4, pp.271-281, 1991

被引用文献数

1

---

Seismic intensity is an important parameter measuring earthquake shaking severity, especially in regions where few strong motion instruments are in operation. This study aims to apply high-precision questionnaire intensity method widely used in Japan to other earthquake countries.<br>Based on the Modified Mercalli (MM) Intensity Scale, an intensity questionnaire form was prepared and survey was conducted for two California earthquakes and the 1988 Nepal-India border earthquake. First, intensity coefficients are assigned to each item category based on the definition of the scale. For each questionnaire, &ldquo;average&rdquo; item intensity is calculated by taking average of intensity coefficients as marked, and also &ldquo;maximum&rdquo; item intensity by taking maximum intensity coefficient among responses.<br>In California, intensities of the USGS isoseismal maps are found larger than the &ldquo;average&rdquo; item intensities and is comparable to the &ldquo;maximum&rdquo; item intensities, presumably because the USGS guideline of intensity assessment is to choose the maximum damage phenomena.<br>In order to solve this discrepancy, we introduced fuzzy set theory and expressed intensity coefficients as distribution of likelihood belonging to continuous intensity level. Accumulating membership functions corresponding to selected item categories, the maximum value of distribution suggests the most probable intensity.<br>New method for questionnaire intensity evaluation is examined for previous data. Questionnaire intensities reasonably correlate with intensities locally reported by the USGS and Nepalese agency. Simple adjustment based on age of buildings is found satisfactory for the case of California but not so for the Nepal-India region.

著者

功刀 卓

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.53, no.1, pp.89-93, 2000-07-25

参考文献数

13

被引用文献数

2 6

著者

鳥海 勲 竹内 吉弘 大場 新太郎 堀家 正則 井上 豊 馬場 研介

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.43, no.3, pp.373-378, 1990-09-24 (Released:2010-03-09)

参考文献数

5

被引用文献数

4 4

---

Seismic wave records at the surface of sedimentary plain are mainly composed of main phase and surface waves. The informations of input wave record in base rock and S wave velocity distribution to base rock are enough to consider the main phase. And moreover the informations about underground structure to bed rock of all sections of plain are necessary to discuss surface wave which travels from surrounding rock range to observation point. For this items of the Osaka plain, there were some crumbs of informations. In 1988, we tried two explosions at a manmade “Hokko” island in Osaka bay. This paper shows the results: five ground structures and a countour map of depth to base rock of the Osaka plain.

著者

関谷 溥

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.3, pp.299-311, 1976-09-15 (Released:2010-03-11)

参考文献数

7

被引用文献数

4 10

---

The Izuhanto-oki earthquake of May 9, 1974 (M6.9) was preceded by an anomalous seismicity as shown Fig. 1. The duration from the anomalous Seismicity to the mainshock was about 10 years and 4 months. Similar phenomena were also found for 10 events which occurred at shallow depths in Japan.Considering that these data show a linear relation between the magnitude of earthquakes M and duration log T (day), the author calculated the coefficient of logT=bM+a by using the method of least squares as follows: logT=bM+a=0.77M-1.65The relation between the above formula and that of TSUBOKAWA (1969), RIKITAKE (1975) and SCHOLZ et al. (1973), which indicate with a certain accuracy the magnitude and time of an expected earthquake was given by Fig. 7.The author believes that the anomalous seismicity preceding earthquakes is one of the potential parameters which could be employed for earthquake prediction. On the other hand, in some certain fracture zones were found a premonitory change before some events. These phenomena generally are called foreshocks. Anomalous seismicity preceding smaller events cannot clearly be found by data of the Japan Meteorological Agency as shown Fig. 8. It is, however, not certain yet whether such earthquakes were not really preceded by anomalous seismicity.Our study requires further accumulation of examples from the viewpoint of ascertaining the existence of anomalous seismicity preceding earthquakes by observation network for small earthquakes.

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. 2輯 (ISSN:00371114)

巻号頁・発行日

vol.46, no.4, pp.461-477, 1994-03-01

参考文献数

63

被引用文献数

2 1

---

Tectonics of the Taiwan region is reviewed. Relative plate motions so far obtained are described and rated. The most reliable solution gives 7.4cm/yr Philippine Sea-Eurasian motion in the N50&deg;W direction in central Taiwan. Plate boundary geometries and modes of plate consumption in the region are discussed on the basis of geophysical, geological and geomorphological data. The major thrust zones at the Western Foothills and the Longitudinal Valley constitute mechanical plate boundaries, but a considerable fraction of the relative plate motion is also consumed by the strike-slip faulting off the southeast coast of Taiwan.<br>The cause for the occurrence of the strike-slip faulting off the southeast coast of Taiwan is discussed based on the various models so far proposed. The bending of the Philippine Sea plate due to the subduction at the Ryukyu Trench and the collision in the Longitudinal Valley are similar to the tectonics of the Izu Peninsula region in Japan, and are the most likely cause for the strike-slip faulting.<br>The reconstruction of the motion and plate boundaries in the vicinity of Taiwan for the past 4-6m. y. is reviewed. The Philippine Sea-Eurasian motion for the past 4 Ma is similar to the present one. The motion prior to 4 Ma may be more northward than present due to the absence of subduction at the Philippine Trench. The Luzon arc started to collide with the continental margin of S. E. China around 4 Ma.

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.1, pp.85-87, 1974-03-30 (Released:2010-03-11)

参考文献数

8

著者

浜田 信生 野坂 大輔 小林 正志 吉川 一光 石垣 祐三 田利 信二朗

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.4, pp.197-209, 2012-06-25 (Released:2012-08-08)

参考文献数

28

---

Matsushiro earthquake swarm is a most well known and well studied earthquake swarm in the history of seismology. From viewpoints of geophysics, geology and geochemistry, various observations, field surveys and analyses had been made to reveal characteristics of the swarm. On the basis of these studies, several models had been proposed to explain why and how the swarm originated and developed. However, majority of studies had focused on the activity around the climatic stage of the swarm in 1966 and so far, studies on the initial stage of the swarm in mid 1965 had remained few due to lack of sufficient observation data. The exact area where the swarm was born had not been known and the swarm was vaguely believed to originate from the area around Mt. Minakami in former Matsushiro town (now belongs to Nagano city). Considering that the manner of initial development of swarm activity represents an important characteristic of the swarm earthquake, we tried to get more clear view about initial stage of the swarm activity in this study. We re-investigated seismograms obtained by routine observation and studied seismograms of temporal stations for the first time which had not been processed yet. By scanning analogue seismograms, we made a complete data set of S-P times with high precision for each station. Although the data set of S-P times from two stations are not sufficient for conventional hypocenter location, we were able to narrow down a possible source area of the swarm activity under the reasonable assumptions. By considering direction of initial motion of P waves and assuming local velocity model of the upper crust in the region and plausible focal depth of 4.5km of the swarm earthquake, we found that the area of swarm in the very beginning in August, 1965 is located about 4km north-east of the Matsushiro earthquake fault (MEF) in former Wakaho town near its border with former Matsushiro town. Size of the initial swarm area was 3-4km in diameter. While swarm activity in the initial region was gradually decaying in September new swarm activity appeared separately from the initial swarm area around southern and south-west part of the MEF. Activity in the new swarm area had been increasing and it was developed to more intense swarm after October, 1965 when establishment of temporal seismic station network of the Earthquake Research Institute, University of Tokyo enabled detailed hypocenter location. The new swarm area coincides with the area where large amount of ground water moved upward and was released on the ground surface in the climatic stage of the swarm. It was well known that source area of the swarm was split and expanded toward north-east and south-west after March, 1967 in its climatic stage. Present study on the initial development of swarm area suggested that characteristics of the Matsushiro earthquake swarm such as splitting and expansion of its source area toward northeast and southwest were inherent in their early stage of the activity in August and September, 1965.

著者

長谷川 昭 海野 徳仁 高木 章雄 鈴木 貞臣 本谷 義信 亀谷 悟 田中 和夫 澤田 義博

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.36, no.2, pp.129-150, 1983-06-25 (Released:2010-03-11)

参考文献数

18

被引用文献数

13 13

---

Precise relocation of earthquakes occurring in Hokkaido and northern Honshu during the period from January, 1979 to October 1981 is made by using 35 stations of the microearthquake observation networks of Tohoku University, of Hokkaido University, of Hirosaki University and of Central Research Institute of Electric Power Industry. Obtained hypocenter distribution shows the double-planed structure of the deep seismic zone in the whole area of Hokkaido and northern Honshu including the junction between the northeastern Japan arc and the Kurile arc. At the junction the deep seismic zone is contorted but is still double-planed at least in the upper 150km depth range. Beneath the southern end of the Kurile arc (central and eastern Hokkaido) the upper seismic plane of the double seismic zone disappears at depths greater than about 120km, whereas the seismicity in the upper seismic plane is still active in this depth range beneath the northeastern Japan arc.Hypocenters on the deep seismic zone beneath Hokkaido, relocated in the present study, are systematically shifted to the SE or SSE direction in comparison with the locations by the Hokkaido University network. This systematic shift of hypocenters is found to be well explained by the existence of the subducted lithosphere with seismic wave velocities higher than the surrounding mantle.

著者

花籠 靖 中西 一郎 森谷 武男 笠原 稔

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.213-225, 1990-06-24 (Released:2010-03-11)

参考文献数

19

---

The rapid determination of seismic moment and source mechanism for near earthquakes is attempted by a moment tensor inversion of long-period seismic waves. The inversion method is based on a normal mode theory. The data for the inversion are recorded at three stations in Hokkaido, Japan. Each station is equipped with a three-components very-broad-band seismograph. Source parameters of six earthquakes (mb_??_5.5) in and around the Japan region (epicentral distances of 200 to 1500km) for the period from January to April 1989 are determind by applying the moment tensor inversion to the long-period waveform data. Changing the components (UD, NS, EW) and record length used in the inversion the stability in the moment tensor solution is examined. A good S/N ratio is required to obtain a stable solution in the inversion of three-components data from a single station. Data length of 4-8min after the earthquake origin time is enough to attain stable source mechanism determination by using the three-stations data.

著者

笹谷 努

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.1, pp.67-76, 1973

被引用文献数

1

---

A particular type of phase designated as the P₂-phase is found in the P wave train around 9 seconds after the first arrival of the earthquake off east coast of Aomori prefecture of March 29, 1965. In the previous paper, the P₂-phase has been interpreted as the stopping phase from the analysis of the motion direction of this phase. In the present paper, the P₂-phase is re-examined in the wave form of the theoretical displacement of P wave from a fault near the earth's surface, because the unreasonable interpretation for the fault length and the rupture velocity has been given. The examination shows that the P₂-phase concerned does not consist of the stopping phase, but of reflected sP phase, and that the wave form of direct P wave from a fault with a fault length greater than its depth may be disturbed by the reflected waves.<br>The seismic moment and the apparent stress for the present earthquake are estimated to be 3.20&times;10²⁵dyne-cm and 5 bars, respectively.

著者

領木 邦浩

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.51-63, 1999-06-30 (Released:2010-03-11)

参考文献数

63

被引用文献数

2 7

---

The regional gravity anomalies were calculated in Southwestern Japan presuming a three-dimensional density structure. The gravitational effect was calculated by the structural model represented by aggregate bodies of triangular vertical prisms which was generated by compiling the existing vast amount of data on the depths of lower surface of the crust and upper surface of the plate slab in this region. The densities of the Pacific and Philippine Sea plate slabs, upper and lower crusts and asthenosphere were presumed referring to past research. It was shown by the calculation that the gravitational effect of the crust has larger amplitude than that of the plate slabs in this region, while variation of the presumptive density of the plate slab is more effective than that of the crust. Comparison of the regional gravity correction by means of the above method with the ones by the spatial filtering method and the least square method shows that the former derives more accurate local gravity anomaly than the latter. The regional gravity anomaly can be calculated by the above method at an arbitrary point in Southwestern Japan, and then more accurate regional gravity correction can be performed for the analysis of local gravity structure.

著者

吉山 良一

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.9, no.6, pp.250-260, 1937-06-15 (Released:2010-03-09)

参考文献数

4

著者

山内 常生 下 道国

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.435-446, 1982-09-25 (Released:2010-03-11)

参考文献数

9

被引用文献数

6 7

---

The concentration of 222Rn in air in the gallery at Mikawa. Crustal Movement Observatory (Toyohashi City, central Japan) has been continuously measured with a flow-type ionization chamber since April, 1977 for the investigation of pre-earthquake anomalies. The observed 222Rn concentration shows remarkable increase after rainfall. It seems that 222Rn rich air is squeezed in the gallery by the contractile force caused by rainfalls from faults with elevated 226Ra content. The variation of 222Rn concentration in the gallery has been calculated from the rainfall data from June, 1977 to December, 1979. Sometimes remarkable disagreements between the observed and calculated values of the 222Rn concentration are seen before and after the occurrence of nearby earthquakes. Such a disagreement might be a precursor of nearby earthquake. The concentration of 222Rn is also influenced by the changes in atomospheric pressure; it increases as the pressure drops and decreases as the pressure rises. Seasonal variations are recognized, too. Continuous observation of 222Rn has also been started in June, 1980 at Kikugawa Crustal Movement Observational Station (Shizuoka Prefecture, central Japan).

著者

松浦 充宏

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.213-227, 1998-03-31 (Released:2010-11-17)

参考文献数

42

被引用文献数

1

---

Physical processes of earthquake generation may be divided into three different stages, such as tectonic loading, quasi-static nucleation, and subsequent dynamic rupture propagation. The basic equations governing the earthquake generation process are; the equation of motion in elastodynamics that relates slip motion on a fault surface with deformation of the surrounding elastic media, the fault constitutive law that prescribes the relation between shear stress and fault slip (and/or slip velocity) on the fault surface during earthquake rupture, and the loading function that gives the increase rate of eacternal shear stress induced by relative plate motion. Recent development in physics of earthquake generation enables us to simulate the entire process of earthquake generation by solving these nonlinear coupled equations. For long-term prediction of earthquake occurrence the detection of crustal movements associated with tectonic loading is important. For short-term prediction the detection of precursory phenomena associated with rupture nucleation is important. In either case it is necessary to establish an interactive forecast system based on theoretical simulation and continuous monitoring of earthquake generation processes.