地震 第2輯
Online ISSN : 1883-9029
Print ISSN : 0037-1114
ISSN-L : 0037-1114
37 巻, 3 号
選択された号の論文の16件中1~16を表示しています
  • 小笠原 宏
    1984 年 37 巻 3 号 p. 357-367
    発行日: 1984/09/25
    公開日: 2010/03/11
    ジャーナル フリー
    In situ stress measurements have been carried out by an “8-element-gauge” method which is one of the stress releasing methods. Several problems remain unsolved in the techniques of measurement and analysis. Their causes are exactly investigated and the accuracy of the stress value estimated is discussed in the present article.
    Data employed for estimating the stress value involve systematic errors. Among them, errors in strain sensitivity matrices and those in rotational angles which determine the angles between each strain gauge and boreholes are predominant.
    In order to reduce the systematic errors, the strain sensitivity matrix is recalculated and the rotational angle is corrected. Results obtained are compared with ones previously determined. The following conclusions are obtained as for the eight sites where the Research Group for Crustal Stress in Western Japan measured in situ stresses.
    (1) Vertical stresses at a few sites previously determined are significantly underestimated, whereas the present ones can be explained by the gravity loading and topographic effect.
    (2) Average horizontal stresses as well as maximum horizontal shear stresses vary by their corrections and are propotional to the depth from the ground surface, except for those at Ohtani mine.
    The accuracy of the stress values obtained by the “8-element-gauge” method is several MPa for the measurements using two boreholes and a few MPa for ones using three boreholes, if the conditions of the measurements are the same as those at eight sites described above.
  • 竹本 修三
    1984 年 37 巻 3 号 p. 369-381
    発行日: 1984/09/25
    公開日: 2010/03/11
    ジャーナル フリー
    The relation between strain changes and amounts of precipitation has been investigated using data obtained from twenty-one crustal movement observatories in Japan. As a possible mechanism to explain this relation, a hydrological model of ground-water flow in a porous medium is considered.
    Observation tunnels, in which extensometers are installed, are generally excavated in rocks containing many cracks or fissures. These rocks near the surface are assumed to be a porous medium. The water level in the medium shows rapid drawdown toward the tunnel because of drainage of ground-water into the tunnel. And the fluid pressure is predominant in the direction perpendicular to the axis of tunnel. Local strains under the action of fluid pressure around the tunnel are calculated with the finite element method.
    Based on this model, observational results obtained from extensometers at Ide, Amagase and Iwakura observatories are explained well.
  • 濃尾平野の深層地震基盤地形
    成瀬 聖慈, 吉田 厚司, 正木 和明, 鏡味 洋史, 宮崎 雅徳, 久保寺 章
    1984 年 37 巻 3 号 p. 383-395
    発行日: 1984/09/25
    公開日: 2010/03/11
    ジャーナル フリー
    The research group for long-period microtremors has long been continuing a series of field observations in view of elucidating dynamic characteristics of deep soil deposit, and has demonstrated that the observation of long-period microtremors is a useful tool for solving this important problem in Earthquake Engineering. However, the research group is afraid such understanding might be produced owing to the fact that the observations were carried out mostly in a specific area of, say, Hachinohe city in northern Japan. To examine this, further observational experiments in the other areas are necessary. This paper reports such an examination.
    A new test field was chosen in and around the Nohbi plain, central Japan, knowing that there are wide-spread and deep-deposited alluvial soils. Another reason is the importance of this area from earthquake disaster prevention point. This area is, centered at Nagoya city, most extensive in industry and commerce and is located in seismically active region.
    The long-period microtremors were observed at 35 points at almost regular intervals of 2km along a N70E-S70W line passing through the Nohbi plain and extending to the outcrop sites of basemental Mesozoic rock. A systematic change of predominant periods of the microtremors was observed in terms of the Fourier spectra. It is between 1.5sec and 5sec, and seems correlated well with a depth to the basemental rock. The similar tendency in predominant periods was also supported by a supplimental observaton of natural earthquakes at several points on the soil and rock sites. A subsoil structure model along the observation line was proposed based upon the result that predominant period of the microtromors is a good index of soil layer thickness. Through this experiment it was reconfirmed that the observation of long-period microtremors provides much data effective for exploring amplification characteristic of deep soil deposit.
  • 跡津川断層・阿寺断層における全磁力調査
    村上 英記, 山田 功夫, 小林 潮
    1984 年 37 巻 3 号 p. 397-405
    発行日: 1984/09/25
    公開日: 2010/03/11
    ジャーナル フリー
    Geomagnetic total force around Atotsugawa fault and Atera fault was observed by the proton magnetometer. Both faults are strike-slip faults of Quaternary age in central Japan and the average rates of displacement are more than 1m/103 year. The characteristic magnetic total force associated with these faults were observed. Although large magnetic anomalies up to 300nT were observed along Atotsugawa fault, magnetic anomalies across Atera fault were about 10 to 80nT. The magnetic anomalies along Atotsugawa fault can be explained by the dyke model that the material with the magnetic susceptibility ranging from 10-3 to 10-2 (SI unit) intrudes along the fault plane. This material may be basic rock or rock contained iron minerals.
  • 多田 堯
    1984 年 37 巻 3 号 p. 407-415
    発行日: 1984/09/25
    公開日: 2010/03/11
    ジャーナル フリー
    The repeated triangulation surveys have revealed the conspicuous N-S extentional strain field in the central Kyusyu. This strain field has been caused by the horizontal crustal movement that the triangulation stations in both the sides of the Beppu-Shimabara Graben have moved away each others to the N-S direction. The Beppu-Shimabara Graben strikes across the central Kyusyu to the E-W direction. The gravity anomaly, the seismological data and other geotectonic data support the idea that the Beppu-Shimabara Graben is a rift of the crust and the north-eastern terminal part of the Okinawa Trough which is the active back arc basin of the Ryukyu Arc and is spreading to the N-S direction. Therefore, it is concluded that the N-S extentional crustal deformation in the central Kyusyu has been caused by the rifting and the spreading of the Okinawa Trough. In other words, the Kyusyu is rifting and spreading to the N-S direction along the Beppu-Shimabara Graben. The spreading ratio is estimated to be about 15mm/a from the horizontal crustal deformation.
  • 小林 芳正, 安藤 雅孝, 入倉 孝次郎, 吉住 永三郎
    1984 年 37 巻 3 号 p. 417-428
    発行日: 1984/09/25
    公開日: 2010/03/11
    ジャーナル フリー
    The Obaku fault is an active fault bounding the south-eastern edge of the Kyoto Basin. The location and underground structure of the fault has been investigated by means of electric-resistivity survey (ρau method), borings and trench excavation. The findings are discussed by comparing existing information on the fault obtained by seismic surveys, observation of microtremors and γ-ray measurements with observation of outcrops made in a construction-work area near the investigated site. This study reveals that the electrical method is effective for detecting discontinuities at shallow depths, and also other geophysical methods have their merits at various stages of investigations of active faults.
  • 林 保彦, 阿部 勝征
    1984 年 37 巻 3 号 p. 429-439
    発行日: 1984/09/25
    公開日: 2010/03/11
    ジャーナル フリー
    The magnitude scale MJ, defined by TSUBOI (1954), is widely used for local earthquakes in Japan. JMA (Japan Meteorological Agency) has officially applied it to amplitude data obtained by the JMA network of seismographic stations. The average period of the waves used is usually about 3sec. The MJ scale agrees approximately with the 20sec surface-wave magnitude MS around MS=7. However, MJ deviates very systematically from MS as MS decreases, and MJ is overestimated by as much as 0.6 at MS=4. For determining the equivalent of MS from JMA data, the new formula is defined to be MS(JMA)=1.32logA+2.61log Δ-4.18, where A(μm) is the combined maximum horizontal amplitudes available from JMA and Δ(km) is the epicentral distance. The new formula is regressed against reliable MS values. The MS(JMAA) and MS values from the observed data are essentially equivalent between MS=4 and 8.5. The coefficient of log A in the new formula is explained from the scaling law of seismic spectra, if the difference of the wave period used between the present study and the original definition of MS is considered.
  • 天池 文男, 竹内 文朗, 春日 茂, 古川 信雄, 平野 憲雄
    1984 年 37 巻 3 号 p. 441-452
    発行日: 1984/09/25
    公開日: 2010/03/11
    ジャーナル フリー
    The past activity of the Fukui Earthquake fault prior to the 1948 event is unknown because the fault is covered by a thick deposit. We estimated the depth of the basement for a profile across the fault by means of seismic exploration using an air-gun as source apparatus as well as by the delay times determined by two natural earthquakes. The basement in the western side was obtained to be deeper by 50-200m than that in the eastern side. The basement estimated in this work, the results of leveling survey before and after the earthquake, the present topography, and the boundary shape between the alluvium and the diluvium across the fault suggest the recurrence of earthquakes associated with this fault. The mean rate of displacement is estimated to be 0.1-1.0m/1, 000 years.
  • 吉田 明夫, 岩田 孝仁, 里村 幹夫, 志知 龍一
    1984 年 37 巻 3 号 p. 453-464
    発行日: 1984/09/25
    公開日: 2010/03/11
    ジャーナル フリー
    The possibility of the existence of an active tectonic line in the west side region of Suruga Bay is investigated. First, some characteristics of seismicity and mechanism of earthquakes occurring in this region are reviewed. Then, a set of faults of NW-SE direction newly found on the shore of Ookuzure-Kaigan is introduced. The fault outcrops are observed at the ends of lineaments clearly seen in an air photograph. Striations on slickensides show that they are left-lateral with slight dip slip movement. These faults are situated just on the E-F line proposed by MOGI (1977), however, slip direction is reverse to the Irozaki fault. On the same part of the west coast of Suruga Bay certain features of boundary are observed in Bouguer anomaly map and in recent crustal strain accumulation as well.
    In the discussion the meaning of the tectonic line is preliminarily considered and the possibility that stress field in the Philippine sea plate differs, in this region, from that in the upper crust of Eurasian plate is proposed.
  • 梅田 康弘, 村上 寛史, 飯尾 能久, 長 秋雄, 安藤 雅孝, 大長 昭雄
    1984 年 37 巻 3 号 p. 465-473
    発行日: 1984/09/25
    公開日: 2010/03/11
    ジャーナル フリー
    Many open cracks were found on the Yayoi-age dwelling site on the Kamo-terrace in Kawanishi City, Hyogo Prefecture. The vertical displacements at some large cracks found on the sectional layer are north up and the maximum displacement is estimated to be 40cm.
    The north up inclination of the Kamo-terrace in the Quaternary period is consistent with the sense of the vertical displacement. It is confirmed that these open cracks were formed not by a land slide but by a large earthquake. However, there is no evidence of such an earthquake in the historical age.
    Arima-Takatsuki tectonic line is located at 500m northward from the Kamo-terrace. It is known that the mountain region divided from the plain by this tectonic line was lifted in Quaternary period. The existence of the cracks on the Kamo-terrace suggests that this tectonic line was activated after the Yayoi-age (B. C. 3c. -A. D. 3c.).
  • 国立防災科学技術センター関東・東海地殻活動観測網
    松村 正三
    1984 年 37 巻 3 号 p. 475-489
    発行日: 1984/09/25
    公開日: 2010/03/11
    ジャーナル フリー
    A method for evaluating detection capability of earthquakes was developed for an observational network. A function expressing detection probability P(M, x) for an earthquake with magnitude M, located at x was defined by combinating the individual detection probability determined for each station.
    By using this formula, the detectable regions of microearthquakes were drawn for the Kanto-Tokai Observational Network of NRCDP, which consisted of 44 seismometer stations as of March 1983. It was confirmed that shallow earthquakes (h≤30km) with magnitude greater than 2.0 could certainly be detected within the network covering the Kanto and Tokai areas. For earthquakes with smaller magnitude, the network has a gap of detectable region around the Boso peninsula.
    For those selected regions of relatively high detection capability, frequency distributions of magnitude were investigated, and b-values and other parameters were obtained. It was found that in most cases, the Gutenberg-Richter's relation was satisfied down to fairly small magnitude of 1.1-2.0, with ordinary b-values of about 0.9.
  • 古川 信雄
    1984 年 37 巻 3 号 p. 491-501
    発行日: 1984/09/25
    公開日: 2010/03/11
    ジャーナル フリー
    A new method is presented to study a fine crustal structure, and has been successfully applied in the eastern Chugoku and western Kinki districts. Using aftershocks of the 1983 Tottori-Ken Chubu earthquake (M6.2) whose epicenters are situated at almost the same place with various focal depths, the velocity gradient in the upper crust (granitic layer) and the position of the Conrad discontinuity have been determined. In this method, sufficient information is given by travel times observed at only one station. Using the relation between travel times of direct P waves and focal depths, the velocity gradient has been determined to be 0.00±0.01sec-1 in the depth range 4-13km, thus the P-wave velocity in the upper crust is almost constant in the concerned districts.
    The waves reflected from the Conrad discontinuity (PXP) are easily found by this method, because the travel-time difference between direct P and PXP waves is more sensitive to a focal depth than to an epicentral distance. The Conrad discontinuity in the central Tottori prefecture is about 16km in depth and this interface is inclined toward southeast by east with a dip angle of -4 degrees. Since almost all recent earthquakes in the Tottori district are shallower than 14km in depth, we conclude that shallow earthquakes in this district have occurred in the upper crust above the Conrad discontinuity.
  • 宮下 芳, 北澤 幸人
    1984 年 37 巻 3 号 p. 503-505
    発行日: 1984/09/25
    公開日: 2010/03/11
    ジャーナル フリー
  • 宇佐美 龍夫, 関田 康夫, 勝間田 明男, 芦谷 公稔, 鹿島 薫, 橋口 能明, 木下 幹夫, 伊藤 純一
    1984 年 37 巻 3 号 p. 506-510
    発行日: 1984/09/25
    公開日: 2010/03/11
    ジャーナル フリー
  • 卜部 卓, 金沢 敏彦
    1984 年 37 巻 3 号 p. 511-513
    発行日: 1984/09/25
    公開日: 2010/03/11
    ジャーナル フリー
  • 綱川 秀夫, 浅田 敏
    1984 年 37 巻 3 号 p. 513-515
    発行日: 1984/09/25
    公開日: 2010/03/11
    ジャーナル フリー
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