測地学会誌
Online ISSN : 2185-517X
Print ISSN : 0038-0830
ISSN-L : 0038-0830
31 巻, 1 号
選択された号の論文の15件中1~15を表示しています
  • 河野 宣之
    1985 年 31 巻 1 号 p. 1-11
    発行日: 1985/06/25
    公開日: 2010/09/07
    ジャーナル フリー
    The very first VLBI observation was carried out only 20 years ago. The recorded bandwidth, which is related to the precision of the estimation of baseline length, was 2.4 KHz in that observation. However, at present, the bandwidth is about 56 MHz and the precision of baseline estimation is within a few cm. Using this system, global observations of plate motion within a few cm accuracy just started this year. More than 20 stations of 5 countries in North America, Europe and Japan participated in these observations. It is certain that these VLBI networks will extend to all plates to monitor their motion. Furthermore, the mobile VLBI system makes it possible to detect regional crustal movements. Thus, the VLBI technique will certainly give new activity to geophysics. On the other hand, in view of the research on the VLBI system, the VLBI technique faces some difficult problems, such as measurement of propagation delay due to the atmosphere, improvement of the physical model, influence of fine structure of QSO etc. Research on these subjects will make VLBI observations within mm accuracy possible in the future.
  • ―.観測の現状―
    藤下 光身
    1985 年 31 巻 1 号 p. 12-19
    発行日: 1985/06/25
    公開日: 2010/09/07
    ジャーナル フリー
    Observations of plate motions and regional crustal deformations using space technology are reviewed. Reviewed technologies in this paper are Doppler observation of Navy Navigation Satellite, Satellite Laser Ranging (SLR) and Very Long Baseline Interferometry (VLBI). It seems that SLR and VLBI detect real crustal movements but the results using satellite Doppler observation are not so clear at this time.
  • ―数値シミュレーション―
    海津 優, 加藤 照之
    1985 年 31 巻 1 号 p. 20-24
    発行日: 1985/06/25
    公開日: 2010/09/07
    ジャーナル フリー
    In crustal dynamics research, it is quite important to study the relation between the tectonic plate motion and the local crustal motion by means of geodetic measurement. Through such study, the mechanism of the local crustal movement will be totally appreciated. Before the space became available, it was impossible to survey a globalscale geodetic network and the plate motion was estimated through indirect geophysical evidences such as seismic slip vector. Recently, owing to the development of space geodesy, it came to be possible to measure direction and length of baselines over thousands of killometers. In this article, the detectability of the tectonic plate motion is discussed through a numerical simulation using a formal error analysis of a VLBI network by comparing the result of simulation with AMl-2 model of the plate motion by Minster and Jordan. The result of simulation shows, for example, that the motion of North American plate relative to Eurasian plate can be detected by two years lasting once a month VLBI observation if there are no systematic effect on the observed VLBI data such as seasonal effect.
  • ―埋込式体積歪計による観測―
    福留 篤男
    1985 年 31 巻 1 号 p. 25-33
    発行日: 1985/06/25
    公開日: 2010/09/07
    ジャーナル フリー
    Japan Meteorological Agency (J. M. A.) is now operating borehole volume strainmeter at thirty one stations in Tokai and Kanto districts. Its main purpose is to catch the precursory phenomena of a great earthquake which is said to possibly occur in Tokai district. However the output signals of the instruments are mixed with various noises from different kinds of sources. To accomplish the main purpose, it is necessary to know the instrumental responses to these disturbances which may contaminate the useful informations. In this paper the instrumental responses of the borehole volume strainmeter to the seismic wave incidence, atmospheric pressure changes and earth tides are reviewed, which has been revealed up to the present. The results are summed up as follows. The observation sites which have high sensitivities to the seismic waves give large amplitudes of earth tides, but do not respond well to the atmospheric pressure change. One of the main causes which give the varieties of these sensitivities is considered to be the difference of Poisson's ratio in each site. Step-like volumetric strain changes due to influences of groundwater and precipitation are also discussed briefly.
  • 坂田 正治
    1985 年 31 巻 1 号 p. 34-45
    発行日: 1985/06/25
    公開日: 2010/09/07
    ジャーナル フリー
    It is crucial to detect short term precursors by continuous observation of crustal deformation in order to succeed in earthquake prediction. For that purpose we need to establish dense networks composed of high-resolution sensors in the areas concerned. Since these areas often include plain field areas, borehole-type observation system is indispensable. This system has many advantages over the conventional valut-type obser vation system; (a) short period for construction, (b) less affected by surface topography, (c) less affected by precipitation and flow of underground water, (d) negligible disturbance due to the smallness of borehole diameter. We have not only developed a force-balanced pendulum type tiltmeter itself but also has been improving borehole drilling techniques and down-hole installation methods for more than a decade. Tiltmeters are installed in boreholes at depths of about 100m. The measurable range is 400 cradian, the resolution is 0.006pradian, and the long-term stability is better than a few microradian per year. We have 24 stations now in operation in the Kanto-Tokai District. Clear records of the earthtide demonstrate the high quality of our observation method. Recently an anomolous tilt change up to 0.4pradian during 10 days was detected before the earthquake of magnitude 6.0, which occurred in the eastern Yamanashi on Aug. 8, 1983. Detection of three components of horizontal strain is preferable for precise understanding of the strain field. A new type of three-component strainmeter was developed based on the invention by Sakata. At first a pair of the instruments were installed and cemented in boreholes at depths of 160 m at Yasato, Ibaraki. They successfully detected clear strain steps of the order of 10-8 caused by the Off-Ibaraki earthquake (July 23, 1982). Observed data from the two instruments agree with each other very well. They are in good harmony with the theoretical results calculated from a fault model. Since then many strain steps have been recorded. Detectable strain steps are as small as the order of 10-10. Such high performances can be attributed to the fact that the whole system is free from solid friction and less affected by shock and vibration at the time of earthquakes. We are planning to develop an IBOS (Integrated Borehole Obsevation System) in the near future. In this system a borehole tiltmeter and a three-component strainmeter are combined to one unit. This system can simultaneously detect five independent com ponents representing crustal deformation.
  • 水野 浩雄
    1985 年 31 巻 1 号 p. 46-58
    発行日: 1985/06/25
    公開日: 2011/07/05
    ジャーナル フリー
     九州及び東北地方の水準測量の資料により,平均距離約35kmにおける大地の傾動運動の統計的考察を行った.時間丁の間に生ずる傾動量β は,正規分布に従う確率変数で,その期待値は零,分散はTに比例することが示された.ただし一部に,一方的な累積により特別に大きな傾動量を示す場合があり,その中には火山活動などの構造運動との関連が考えられるものもある. 解析の過程で,水準測量の精度が見積られた.その誤差は一般に,0.7mm/√kmの偶然誤差の伝播によるものであり,系統誤差は考慮の必要がないことが示された.
  • 山内 常生
    1985 年 31 巻 1 号 p. 59-72
    発行日: 1985/06/25
    公開日: 2011/07/05
    ジャーナル フリー
    Continuous observations of crustal movements in tunnels, which have been carried out in various regions in Japan since 1930's, provide valuable information about the ground deformations related with earthquake occurrences. The author summarized the precursory ground strains and tilts that had been reported since the last symposium in 1972 on the earthquake prediction research in Japan. They amounted to 30 cases during the last decade. These data suggest that continuous observation of crustal movement in and near a fractured zone plays an important role for the detection of earthquake precursor. Fractured zones seem to amplify precursory phenomena. A typical example was the observation at Yasutomi station on the Yamasaki fault, known as a quaternary active fault. It was reported that anomalous slip movements in the fractured zone after rainfall were clearly observed during few days prior to the increase in the activity of microearthquakes. It has been clarified that at some observatories, a strain response to rainfall shows temporal variations which may be related to an occurrence of earthquakes around the observatories. The author has applied a tank model to simulate normal strain responses to rainfalls at the Mikawa Crustal Movement Observatory. Abnormal strain responses to rainfalls can be detected by this simulator. 24 cases of abnormal responses were recognized during the period from January, 1973 to December, 1983. It seems that underground water makes a notable contribution to such a phenomenon. The relationship between the logarithmic precursor-times and the earthquake magnitudes for the present 30 precursory data is expressed by a linear function. The precursor-time, for a large shock, obtained by a least squares fitting is shorter than that of Rikitake's one.
  • 田中 豊
    1985 年 31 巻 1 号 p. 73-85
    発行日: 1985/06/25
    公開日: 2010/09/07
    ジャーナル フリー
     地震予知の基礎的研究として,1978年以来大学,国立防災科学技術センター,地質調査所は,応力解放法,水圧破壊法,その他新開発された方法により応力測定を実施してきた.1984年中期までには地下開発設計や地熱開発計画に際し実施された測定を含めて50余地点の測定結果が報告された. これらの測定成果を概括し,方法,條件,地域を異にする測定値を比較し,現時点での応力測定の有意性を検討しておく必要がある.理論的厳密な補正は今後の研究を待つこととし,比較のため簡便なデータ処理を施し,応力測定成果を概観することにした. 1)水平最大応力方向は平均的にはテクトニツクな応力状態を十分反映していると思われる. 2)応力深度勾配は各地でそれぞれ異なる.応力解放法では限定地域内で西日本の標準応力深度勾配を求め,これと水圧破壊法による勾配と比較した.平均水平応力,水平せん断応力に関しては,西日本の深度勾配は水圧破壊法により東日本各地で得られた値のほぼ平均を示し,深度勾配の比較は,地下の応力状態を推定し,応力区を類別するために有用と思われる.3)応力深度勾配を用い,各深度の測定値を標準深度(今回300m)の応力値に換算し,水平主応力の地域分布図を画いた.これは応力区の広がり7活断層との関連,局地的異常など壷調べる上で有効と思われる.4)極浅発地震の発震機構から中間主応力軸は必ずしも鉛直ではないことが知られている.上部地殻の応力状態を明解に.示すたあ,3次元応力測定で得られた最大せん断応力面をステレオ投影した.これは地形影響の判定と同時に,活断層地域の局所的応力状態の推定にも役立つ. 以上のように各種の応力測定は十分地震予知の基礎研究として成果をあげつつあるが,応力変化を求めるにはまだ精度が不足であり精度向上と同時に,各種條件下の多数の測定資料がなお必要である.
  • 横山 泉
    1985 年 31 巻 1 号 p. 86-96
    発行日: 1985/06/25
    公開日: 2010/09/07
    ジャーナル フリー
    This is an essay on the contrast between tectonic earthquakes and volcanic eruptions, especially from a standpoint of ground deformation.
  • 箕浦 幸治
    1985 年 31 巻 1 号 p. 97-105
    発行日: 1985/06/25
    公開日: 2011/07/05
    ジャーナル フリー
    The present geomorphic feature of Northeast Japan, which is characterized by three rows of elevated zone and narrow depressions placed among them, has been established by Neogene Green Tuff activity. Pre-Tertiary basement rocks are developed in the elevated zones, and in particular are widely distributed in the outer row (Abukuma- Kitakami Mountains) occupying almost all of the area. The basement rocks are composed of two Jurassic accretionary bodies and a few Siluru-Jurassic micro-continents. These geologic bodies were collided and accreted in late Jurassic and early Cretaceous in the marginal area of east Asia. After the collision and accretion, Northeast Japan had been released from extensive tectonic movement for about 80 million years. 23 million years ago, Green Tuff activity was happened with andesitic volcanism. It has been emphasized that Neogene tectonism of Northeast Japan was closely related with volcanic activity. Many models explaining Green Tuff activity and the tectonic development have been proposed. Plate tectonic theory of active margine seems to be fairly effective for the explanation. From middle Jurassic, Northeast Japan has been situated in the convergent boundary area. Oceanic plate subduction triggered off the separation of Northeast Japan from Asian continent in Palaeogene. Eastward migration of Northeast Japan caused the opening of the Sea of Japan. Neogene intense volcanism and thick sediment accumulation is supposed to be closely related with the migration. Quaternary andesitic volcanos were formed under west-east compressional field, and most of them are situated in the middle row (Ou backbone ranges).
  • ―いつプレート境界が北海道中央から日本海東縁にジャンプしたか?―
    瀬野 徹三
    1985 年 31 巻 1 号 p. 106-123
    発行日: 1985/06/25
    公開日: 2011/07/05
    ジャーナル フリー
     東北日本が北米プレートの一部であるという説が,主として日本海縁部,フォッサ・マグナでのデータをもとに唱えられている.一方,東北日本がマイクロ・プレートであるという説が南関東のデータをもとに唱えられている.ここではこれらの説を検討するために北海道の第四紀の地殻活動を調べた.北海道の第四紀後期の活動はその南部に集中しており,これは千島前弧の横ずれ運動と日高山脈付近での衝突によってよく説明できる.従って北海道の中軸部でのユーラシア-北米プレート間の衝突はすでに活動を終えており,プレート境界の転移はほぼ完了しているといえる. 房総沖海溝三重点付近の地形は,東北日本のユーラシア-北米変換が0.5Maころ起きたことを示唆する.西南日本の東西方向の圧縮応力に伴う地殻変動,いわゆる六甲変動の開始は約0.5Maであり,これはフォッサ・マグナでの衝突の開始がユーラシア-北米変換によって始まったことを意味しているのであろう.したがって東北日本の北米変換は地質学的タイム・スケールでは0.5Ma頃に起こり,現在では完了しているとみられる.
  • 高木 章雄
    1985 年 31 巻 1 号 p. 124-146
    発行日: 1985/06/25
    公開日: 2010/09/07
    ジャーナル フリー
    The most recent data obtained from the high gain seismograph network and the exact leveling in Tohoku District, northeastern Honshu, Japan, are used to investigate seismic activities and tectonics in the northeastern Japan Island Arc. The location of the plate boundary between the descending lithospheric slab and the mantle above it was clearly determined from the difference in arrival times between the ScS and ScSp waves. Accurate determinations of microearthquake hypocenters have led to conclusive evidence that the boundary is located on the upper plane of the double planed deep seismic zone. The Miyagiken-oki Earthquake with M7.4 occurred on June 12, 1978 off the coast of Miyagi Prefecture. The data obtained from the seismograph network of Tohoku University are made the best use of an investigation on seismic activity before and after the main shock. The followings became clear after the detailed analyses on the spatial distribution of main shock and aftershocks. The main shock and almost all the aftershocks occurred at the boundary between the oceanic slab and the overriding continental lithosphere. Focal-mechanism solutions of the main shock and aftershock indicate that these earthquakes are characterized by the low angle reverse faulting. We apply a two-dimensional finite element method to estimate the crustal movement connected with plate movement, by using a proposed model in which the lower crust and the upper mantle are assumed to be viscoelastic materials. It is revealed in the model above mentioned that mutual movement at the boundary between descending oceanic slab and the continental lithosphere above it, is more fast at the region from the trench to the a-seismic front compared with that of other boundary, as the result of the calculation on the crustal movement on land caused by the subducting plate. We may conclude from the results of numerical computations that the distribution of crustal stress is clearly related to the change of crustal structure, and lead to the recognition that the precise determination of the crustal structure is of very importance.
  • 土屋 淳, 田中 寅夫, 河野 芳輝, 細山 謙之輔
    1985 年 31 巻 1 号 p. 147-154
    発行日: 1985/06/25
    公開日: 2011/03/01
    ジャーナル フリー
  • 檀原 毅
    1985 年 31 巻 1 号 p. 155
    発行日: 1985/06/25
    公開日: 2010/09/07
    ジャーナル フリー
  • 笠原 慶一
    1985 年 31 巻 1 号 p. ii
    発行日: 1985/06/25
    公開日: 2011/03/01
    ジャーナル フリー
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