著者

村田 正秋 山本 富嘉 浜田 康弘

出版者

The Geodetic Society of Japan

雑誌

測地学会誌 (ISSN:00380830)

巻号頁・発行日

vol.37, no.1, pp.31-42, 1991

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GPS(全世界測位システム)衛星の軌道決定システム(MSOP)を開発した.MSOPは多衛星同時軌道決定プログラムで,疑似距離データからGPSの宇宙部分を構成する衛星群の軌道を同時に決定することを目的としている.ここでは,太陽輻射圧とyバイアスのモデリングを中心に,GPS衛星の精密軌道決定のための手法を検討し,実際にCIGNETデータによって軌道決定実験を行ない,GPSの測地利用に望まれるサブppmの衛星位置精度が達成されていることを示す.軌道精度の評価は,CIGNETのPコード疑似距離データからMSOPによって決定された軌道を,米海軍兵器センター(NSWC)の精密暦と直接比較することによって行なう.その結果,疑似距離によるGPS衛星の軌道決定精度はa全衛星平均で10mすなわち0.5ppmより良好であることが示された.

著者

飛田 幹男 宗包 浩志 海津 優 松坂 茂 黒石 裕樹 眞暗 良光 加藤 敏

出版者

日本測地学会

雑誌

測地学会誌 (ISSN:00380830)

巻号頁・発行日

vol.50, no.1, pp.27-37, 2004-03-25 (Released:2010-09-07)

参考文献数

14

被引用文献数

1

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The source of seasonal groundwater level variation, which is closely related to the variation of GPS vertical component, was investigated. We found that groundwater pumping for paddy field irrigation from May to August caused drawdown of groundwater level by 7m and this caused temporal subsidence by about 2 cm in Geographical Survey Institute, Tsukuba. Elastic deformation of gravel layers explains the process that groundwater level variation causes variation of ground height, because the height recovers completely and there is no delay between the two variations. The scale error of GEONET due to the seasonal height variation of the fixed GPS station at GSI is estimated to be±0.3 ppb.

著者

松本 晃治

出版者

日本測地学会

雑誌

測地学会誌 (ISSN:00380830)

巻号頁・発行日

vol.50, no.3, pp.187-200, 2004-09-25 (Released:2010-09-07)

参考文献数

32

被引用文献数

1 1

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In order to reduce the tidal errors in the shallow water region, we established a global ocean tide model (NAO.99b) representing major 16 constituents with a spatial resolution of 0.5°. The key feature of this model is a fine-scale along-track tidal analysis of the TOPEX/POSEIDON data, the results of which are assimilated into a barotropic hydrodynamical model which account for the self-attraction and the loading effect accurately. Also we developed a high-resolution (1/12°) regional ocean tide model around Japan (NAO.99Jb) by assimilating both the TOPEX/POSEIDON data and the data of 219 coastal tide gauges. These models with a computer code for tidal loading calculation have been freely distributed via a web site to whomever interested including eodesits and ocennogrnnhers.

著者

藤井 陽一郎

出版者

日本測地学会

雑誌

測地学会誌 (ISSN:00380830)

巻号頁・発行日

vol.23, no.2, pp.74-81, 1977-09-25 (Released:2010-09-07)

参考文献数

9

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Most of abrupt coastal upheaval associated with earthquake are interpreted as result of reverse faulting with low dip angle. The results of levelling suggest a possibility that seismic crustal upheaval along the coast of Sanriku, northeast Japan, were associated with the 1933 Sanriku-oki earthquake with magnitude 8 .3, although the earthquake is normal faulting on the Japan trench. In order to test whether the earthquake could have given coastal upheaval or not, crustal movements are calculated with the following fault parameters for the 1933 Sanriku-oki earthquake;Strike of fault N3°ELength of fault 300 kmWidth of fault 100 kmDip angle 45°Normal slip 6.6 m The results show a 4-6 cm seismic upheaval along the Sanriku coast and horizontal crustal strain with 2-4×10-6 in the east and middle part of northeast Japan . This normal faulting of the 1933 earthquake gave additional crustal strain and would be a trigger of some geophysical phenomena such as earthquake swarms or occurrence of deep earthquakes.

著者

檀原 毅

出版者

日本測地学会

雑誌

測地学会誌 (ISSN:00380830)

巻号頁・発行日

vol.17, no.3, pp.100-108, 1972-03-25 (Released:2011-03-01)

参考文献数

16

被引用文献数

1

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The precise levelling in Japan commenced in about 1884. Past surveys were irregular as regards both repeating interval and area. However, it is possible to arrange them into 4 epochs of reduction. In this report, synthetic vertical movements in the whole land of Japan during the period from about 1895 to about 1965 is studied. Principles of the present reduction are as follows; (1) As 4 epochs of reduction, 1895, 1930, 1950 and 1965 are adopted. (2) Many studies of movements in particular regions and of particular periods have been made by various authors. These results are used for compilation with the synthetic movements. New data in the recent 10-20 years are com-puted this time. (3) Change in mean sea level is used for given conditions in reduction of the recent survey. Number of the adopted tidal stations amounts to 8. (4) In order to obtain a map which is significant for neotectonics motion, abrupt and large movements influ-enced by earthquakes are eliminated as far as possible. (5) By the similar reason as (4), influence of artificial ground subsidence is eliminated. (6) In order to secure nearly equal accuracy all over the whole land, 4-5 bench marks in each mesh of longitude 1° by latitude 1°, are selected to draw a contour map. Fig. 4 shows the final result. The contour is drawn in unit of mm/year. From this figure, the following distinctive movements can be found. (1) The amount of curstal movements in almost all the coastal areas of Japan Sea of Hokkaido and Honshu Islands is small, and it is safely said that these areas are stable. On the contrary, considerably large subsidence is seen in the area of Pacific Ocean side of Hokkaido and the northern part of Honshu Islands. These two facts seem very favorable to an explanation by the plate tectonics; that is, the subsidence of the continental crust is explained by drag down of the sinking lithosphere. (2) In the central part of the Honshu Island, considerable large zone of upheaval can be clearly seen. The northern part of this zone coincides with active volcanic chains, so it can be considered that the volcanic activity still accompanies the land rise. On the other hand, the southern part of the concerned zone is not volcanic area but old moun-taneous region. So it should be considered that this zone continues to the upheaval zones which are seen in Kui Peninsula and Shikoku Island. (3) In the western half of Honshu, Shikoku and Kyushu Islands, it is very remark-able that upheaval and subsidence zones are seen alteratively in parallel to the island arc. This phenomenon may be understood as the folding motion caused by horizontal pressure which acts in perpendicular to the island arc. The half wave length of this motion is about 100 kms. Here only 3 main distinctive movements of Japan Islands in the recent 70 years are cited. The author is apt to consider that almost all these movements are understood on the basis of the plate tectonics. The conclusion, however, is not definitive up to the time when reliable horizontal movements are obtained, because horizontal movements are probably more primary than vertical movements in the field of the plate tectonics.

著者

大坪 俊通 中村 信一 佐藤 まりこ 國森 裕生

出版者

日本測地学会

雑誌

測地学会誌 (ISSN:00380830)

巻号頁・発行日

vol.59, no.3, pp.79-86, 2013 (Released:2015-07-11)

参考文献数

18

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Geodetic laser ranging activities in Japan are reviewed in comparison with the worldwide perspective, in terms of terrestrial tracking stations, satellite missions and scientific analyses. Being severely understaffed, three laser ranging stations, three associate analysis centers, and a number of satellite missions have been successfully operated, and a number of significant contributions have been made to the international community in both science and technology. In the future, we should strive to focus more on domestically-produced technologies, educational paths, and multiple-technique integration.

著者

名和 一成 杉原 光彦 村田 泰章 風間 卓仁 西田 究 菅野 貴之 小山 悦郎 大久保 修平 奥田 隆

出版者

日本測地学会

雑誌

測地学会誌 (ISSN:00380830)

巻号頁・発行日

vol.54, no.2, pp.59-67, 2008 (Released:2013-02-25)

参考文献数

17

被引用文献数

1

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We carried out continuous gravity observation with a Scintrex CG-3M gravimeter at Asama Volcano Observatory from September 4 to October 22 in 2007.We tried to detect hydrological gravity effects after heavy rainfall by Typhoon 200709 (FITOW). To detect hydrological gravity effects we supposed a simple tank model as proposed for the Matsushiro superconducting gravimeter observation, which model represented immediate gravity increase and gradual decrease after rainfall. Parameters of the tank model were estimated using an ABIC minimization iversion method and precipitation data as inputs. As a result, hydrological gravity effects were extracted from gravity residuals although gravity residuals included a large non-linear drift. And the extracted hydrological gravity effects corresponded to temporal gravity changes simultaneously observed with an FG5 absolute gravimeter. Our success promises expanding opportunities of continuous observation by using CG-3M gravimeters in the future.

著者

田島 広一 井筒屋 貞勝

出版者

日本測地学会

雑誌

測地学会誌 (ISSN:00380830)

巻号頁・発行日

vol.17, no.4, pp.187-190, 1972-08-02 (Released:2011-03-01)

参考文献数

4

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Measurements of vertical gradient of gravity carried out at Keio Plaza Hotel Building which was built recently. This building is in Tokyo (latitude: 35°41.2'E longitude: 139°41.9'N) and its height is about 170 m above the ground. The mean value of the gradient measured was 0.3049 mgal/m ± 0.00032SD. There are four stations where the vertical gradients of gravity have been measured in and around Tokyo. The distribution has a tendency to increase toward north in this area same as the free air anomaly distribution.

著者

大野 圭太郎 太田 雄策

出版者

日本測地学会

雑誌

測地学会誌 (ISSN:00380830)

巻号頁・発行日

vol.64, pp.39-50, 2018 (Released:2018-10-26)

参考文献数

27

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Rapid understanding of the magnitude of large earthquakes in the offshore region and their associated fault expansions is important for near-field tsunami forecasting. Since September 2012, the Geospatial Information Authority of Japan (GSI) and Tohoku University have been jointly developing the GEONET real-time analysis system (REGARD), which is expected to provide reliable earthquake magnitude estimation. The REGARD system has two different types of coseismic fault model estimation systems. The first system estimates the slip distribution along the plate boundary, while the second comprises single rectangular fault model estimation. One of the challenges of REGARD is the difficulty in the estimation of the quantitative uncertainty in the single rectangular fault estimation. Thus, we focused on quantitatively understanding the single rectangular fault model estimation based on real-time GNSS time series data. We adopted Markov Chain Monte Carlo methods (MCMC) for modeling of the coseismic single fault. We applied the Metropolis–Hastings MCMC method to the 2011 Tohoku-Oki earthquake. The results obtained clearly demonstrated the tradeoff between the fault area and the amount of slip. The posterior probability density function (PDF) of the obtained slip amount showed a complex shape compared with those for the other unknown parameters. Thus, we focused on the stress drop value. Based on multiple Markov chains using Gaussian prior PDF for the stress drop with different mean value (5, 10, 15, 20, and 25 MPa), we successfully obtained the simple posterior PDF shape of the slip amount for each different mean value condition. We also found that the entire fault model explained the data well. These results suggest that the data cannot resolve uncertainties from the tradeoff between the fault area and the slip amount, which are extremely important factors for precise near-field tsunami forecasting. The results obtained using different constraint condition for the stress drop by prior distribution may provide the quantitative uncertainties for the resulting tsunamis.

著者

石川 甲子男

出版者

日本測地学会

雑誌

測地学会誌 (ISSN:00380830)

巻号頁・発行日

vol.26, no.1, pp.50-58, 1980

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The problem of geomagnetic secular variation at Kanozan has been reported already by the author. In this report, the geomagnetic monthly mean values of Kanozan Geodetic Observatory were compared with those of the other observatories (Memanbetsu, Mizusawa, Kakioka and Kanoya), during the period from Jan . 1961 to Dec. 1979. From the results, it seems that the secular variations of differences of the geomagnetic field between Kanozan and other observatories are larger than its normal values .

著者

岩田 隆浩 南野 浩之 佐々木 健 小川 美奈 並木 則行 花田 英夫 野田 寛大 松本 晃治 今村 剛 石原 吉明 鶴田 誠逸 浅利 一善 劉 慶会 菊池 冬彦 Goossens Sander 石川 利昭 河野 宣之 高野 忠

出版者

The Geodetic Society of Japan

雑誌

測地学会誌 (ISSN:00380830)

巻号頁・発行日

vol.55, no.2, pp.135-150, 2009-07-25

被引用文献数

10

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SELENE Main Orbiter (KAGUYA) has separated two small sub-satellites; (1) the Relay Satellite "OKINA (Rstar)", and (2) the VLBI Radio Satellite "OUNA (Vstar)". These sub-satellites started to perform 4-way Doppler measurements using Relay Satellite Transponder (RSAT) and multi-frequency phase-delay differential VLBI using VLBI Radio Sources (VRAD) for lunar gravity mapping. We have developed the frequency conversion system, multi frequency S/X-band vertical dipole antenna, and light weighted S-band patch antenna to perform these missions. Simple structured release mechanism has also been developed and confirmed its performance by ground test and orbital demonstration using micro-Lab Sat.<BR> Initial check out were executed and properties of satellite bus equipments, onboard mission instruments, and observation systems including ground stations were evaluated. Electric power and thermal control subsystems have shown that they conduct as designed and inspected in the ground tests. The release mechanisms have given the spin which can maintain the stability of the satellite attitudes. Communication functions of mission instruments conform to the link budgets. These results suggest that OKINA and OUNA have enough performances to produce efficient data by RSAT/VRAD gravity observations.

著者

小野寺 栄喜

出版者

日本測地学会

雑誌

測地学会誌 (ISSN:00380830)

巻号頁・発行日

vol.36, no.4, pp.267-276, 1990-12-25 (Released:2010-09-07)

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The Antarctic Circumpolar Current (ACC) is the only tonal ocean flow around the axis of Earth's rotation. It can directly exchange the angular momentum with Earth's rotational motion. The Trans-Polar Index (TPI), variations of the pressure at the sea surface and the air temperature in the Antarctic show correlations with variations of the length of day (lod). Excitations of the Earth's rotational speed are estimated by using variations of the tonal current of the ACC, which are derived from geostrophic balance approximation of the pressure difference at the surface along the meridian. The pressure difference along the meridian is obtained by two methods; one is from the TPI and another is derived from atmospheric temperature at the surface in the Antarctic and the surface pressure at Ushuaia, in front of the Drake Passage. From the estimated excitation of the Earth's rotational speed, the ACC has proved to contribute to the exchange of the angular momentum with the solid part of the Earth. The ACC has also proved to be coupled with the increasing and/or decreasing of the El Nino.

著者

村上 真幸 中堀 義郎

出版者

日本測地学会

雑誌

測地学会誌 (ISSN:00380830)

巻号頁・発行日

vol.32, no.4, pp.303-309, 1986

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国土地理院では,地震予知観測の一環として,重力の経年変化を求めるための重力測量を実施している.本稿では1982年から1986年にかけて実施した4つの重力点における絶対重力測定の結果を報告する. 測定に使用した装置は佐久間式可搬型絶対重力計で投げ上げ法を採用している.この装置は,国際度量衡局(BIPM)とJaeger社により開発され,1980年に国土地理院に導入された後,改良を加えられてきたものである. 国土地理院は絶対重力測定の一方で,ラコスト重力計による相対重力測定を水準測量と同時に実施している.これにより,全国的な重力網を構成し,かつ,重力の相対変化と地殻の上下変動のデータを蓄積してきている.今回の観測により,この重力網に絶対的な基準を与えることが可能となった.今後,1年に2~3点の絶対測定を4~5年周期で繰り返し実施することにより,重力の絶対変化を検出して地震予知に貢献することが期待される. 現在までに,絶対測定は筑波,柿岡,鹿屋,新十津川の4点で行われている.絶対重力値はいずれも0.01mgalより良い精度で決定されている.絶対測定と同時期に,ラコスト重力計を使って重力の鉛直勾配も決定して,絶対重力値の補正を行っている. 筑波の絶対測定値を,中川他(1983)による相対測定の結果を利用して,米国デソバーで複数の外国の機関によって行われた絶対測定値と比較した.その結果,それぞれの値は良く一致することがわかった.また,柿岡においては,我々の測定と相前後して緯度観測所による絶対測定が行われた.これにより,国内で初めて異なる装置による絶対重力値相互の直接比較が行われたことになる.この比較の結果,両者の間には0.067mgalという有意な差が見い出された.

著者

黒石 裕樹 村上 真幸 海津 優

出版者

The Geodetic Society of Japan

雑誌

測地学会誌 (ISSN:00380830)

巻号頁・発行日

vol.38, no.1, pp.63-74, 1992

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国土地理院が構築した日本重力基準網1975(JGSN75)は,わが国における全ての重力測定の基準値を提供してきた.この網は国際重力基準網1971に準拠しているが,絶対重力測定を全く含んでいない.国内では,近年重力測定が高精度かつ高密度に行われるようになり,基準となるJGSN75の,絶対値の精度の向上が求められるようになった.そこで,国土地理院では,絶対重力計を導入して重力網の高精度化を図ることとした.筆者らは,佐久間式絶対重力計を改良し,1985年以来全国12ヶ所の基準重力点において重力絶対値を決定してきた.それらの観測結果から,絶対重力測定は精度及び再現性とも10μGalよりも高いことが確かめられた.これらの基準重力点を骨格として, 全国約300点から成る一等重力網を構築し,第一回観測を1991年末までに終了した.北海道地区の一等重力網について試験的に行われた網平均結果から,この網全般にわたり,ほぼ10,uGalの精度で重力値が決定されることを確認している. 日本列島は,地震や火山噴火などの地殻活動が極めて活発な地域に位置している.それらの活動に伴う地殻上下変動の検出は,地震や火山活動の予知の研究において極めて重要な課題である.これまで,主に験潮や精密水準といった測量によって,相対的な上下変動の検出が行われてきた.これに対し,地殻活動に伴った重力変化は,地殻上下変動の絶対的な量について重要な情報を提供することが知られている.そこで,国土地理院では,絶対重力測定と一等重力測量を,一等水準測量と併せて5ないし7年を周期として繰り返し行うことを計画している.10μGa1の重力変化は,3~5cmの地殻上下変動に相当することから,一等重力網により,全国にわたり,地殻上下変動を数Cmの精度で監視することができる.また,一等水準測量結果との比較により,地殻上下変動のプロセスを解明することが期待できる.従つて,絶対重力測定に基づいた一等重力・水準網の確立により,地殻上下変動の高精度監視網が構築されたといえる.

著者

坪川 恒也

出版者

The Geodetic Society of Japan

雑誌

測地学会誌 (ISSN:00380830)

巻号頁・発行日

vol.50, no.4, pp.281-294, 2004-12-25

被引用文献数

2

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佐久間式絶対重力計で有名な佐久間晃彦先生が,2004年8月19日パリ郊外セーブル市の自宅で逝去されました.享年73歳.謹んでご冥福をお祈り致します. 先生は,昭和6年宮城県仙台市にお生まれになり,昭和28年(1953)東北大学理学部物理学科卒業と同時に,当時の通産省中央計量検定所(現在の産業技術総合研究所,計量研究所)に入所され,日本で最初に自由落下方式による絶対重力計の開発を手掛けられました.その後,昭和35年にフランスに渡り,国際度量衡局(BIPM)の研究員として,平成8年までの36年間に渡って,重力加速度の絶対測定の研究に従事され,特に,佐久間式と総称される,投げ上げ方式の絶対重力測定法の確立および製品化と,絶対重力網の整備に大きな功績を残されました.まさに絶対重力測定の研究に,半生を捧げられたと言っても過言ではありません.佐久間先生がBIPMに入所された頃は,国際機関とはいえ白人主導の組織の中で,日本人が単独で乗り込んで研究することに,かなりご苦労されたのではないか,と推察致します.そのような環境の中でも,絶対重力測定をテーマとした精密計測に対する佐久間先生の熱いお気持ちが,あのように独創的な絶対重力計として実を結び,まさに日本人の優秀さを世界に認あさせたのではないでしょうか. 佐久間先生には,緯度観測所の固定局型の佐久間式絶対重力測定装置の導入当時から,ご指導頂きました.穏やかな物腰ながら信念を持った,古き良き時代の典型的な日本人との印象を受けました.図1は1989年の第3回絶対重力計国際比較測定をBIPMで主催された時のスナップショットです.ここでは,佐久間先生という偉大な大先輩を偲んで,絶対重力計の開発に携わってきた一人として先生を偲びつつ,絶対重力計開発の経緯と現状について述べたいと思います.

著者

土井 浩一郎 塚本 博則 里村 幹夫 中川 一郎 中村 佳重郎 東 敏博

出版者

日本測地学会

雑誌

測地学会誌 (ISSN:00380830)

巻号頁・発行日

vol.34, no.1, pp.59-70, 1988

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同じコソクリート台の上に設置された2台のLaCosteamp;&Romberg重力計D-58とG-680を用いて,1984年9月から1985年7月にかけての約11ヵ月間にわたり,重力の潮汐変化の連続観測が静岡において行なわれた. 同一地点に設置されている重力計に与える気温,気圧および海洋潮汐などの擾乱源による:影響はほぼ共通していると考えられるために,2台の重力計によるデータからは,調和解析により,類似の結果が得られるであろうと予想される.しかし,実際には,2台の重力計による約11ヵ月間のデータを用いて求められたδ一ファクターは,LaCoste&Romberg重力計G-680から得られたもののほうがやや大きい値を示し,時間変化の様子もあまり似ていなかった.その原因については,現在のところ,まだ解明されていない. LaCoste&Romberg重力計D-58より得られた同時観、測の約11ヵ月間のデータとその期間を含む約2年間のデータからそれぞれ得られたδ一ファクターを比べてみると,0.1%程度でよく一致しており,ほぼ1年間のデータを用いて解析がなされた場合は,きわめて安定した結果が得られることが確かめられた. 地震予知に対する応用においては,より短い解析期間を用いて,より高い精度の解析結果が得られることが要求される.そこで,解析に用いられるデータ期間の長さと2台の重力計で得られたδ一ファクターの差の関係を調べてみた.その結果,解析期間の長さを30日以上とした場合,比較的安定した結果が得られるものの,その変動はかなり大きいことがわかった.

著者

山佳 典史 名和 一成

出版者

日本測地学会

雑誌

測地学会誌 (ISSN:00380830)

巻号頁・発行日

vol.66, pp.16-22, 2020 (Released:2021-04-22)

著者

原田 健久 松村 正一

出版者

日本測地学会

雑誌

測地学会誌

巻号頁・発行日

vol.35, no.1, pp.1-10, 1989

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A rigorous program of adjustment for any geodetic network must have a useful file of geoidal heights in its own to adjust strictly observations by GPS for space vectors. The program, by which geoidal heights can be automatically computed without missing its fine undualtion at every point where vertical deflection is observed, was newly added to the Universal Program of geodetic net-adjustment. The conventional method to find geoidal heights successively along routes linking neighboring vertical deflection points seems not elegant mathematically, because selections of routes are too arbitrary. It ishighly mathematical to find out geoidal heights at all vertical deflection points badjusting simultaneously all observation equations of vertical deflections which are ex pressed as the function of their geoidal heights. Although it seems geophysically reason able that geoidal heights are expressed by a curved surface with the mathematical formula written by coordinates on the surface of the earth, we are afraid that it might miss local fine undulation of geoid. In order to adjust rigorously geodetic network including GPS-observations, it is desirable that every vertical deflection point has its more reliable geoidal height. Vertical deflection at a point is decided by a local shape of the geoid around it. Then we think a new method as follows : Q We make a local geoid by using geoidal heights (rough height+small unknown correction) at several vertical deflection points inside a circle drawn around a vertical deflection point. Q2 We make both observation equations for I(north-south component) and (east-west component) of vertical deflection at thecentral point by considering the difference between geodetic longitude (latitude) and computed astronomical longitude (latitude) to be the direction of normal to the local geoid through the point. (3) We can find better geoidal heights at all vertical deflection points by solving simultaneously all observation equations by means of the method of least squares. How to derive a local geoid mathematically is the most important problem in abovementioned method. A curved surface with higher order terms requests many surrounding points. Reliability of local geoid made by using remote points deteriorates. Vertical deflection points are distributed locally in remarkable high and low densities. We adopted the following sophisticated way with much freedom after considering those peculiarities above.

著者

山本 明彦

出版者

日本測地学会

雑誌

測地学会誌 (ISSN:00380830)

巻号頁・発行日

vol.35, no.2, pp.215-225, 1989-06-25 (Released:2011-03-01)

参考文献数

22

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最近の深発地震の研究から,西南日本において南海・駿河トラフに沿って沈み込むリフィリピン海プレートは,東海地方と紀伊半島で南に凸の等深発地震面を持ち,これらの境界ではcuspを形成していることが明らかになってきた.一方,濃尾平野から琵琶湖にかけての広い地域でブーゲ異常が負になり,特に強い負の領域が濃尾平野と琵琶湖周辺にあることは以前より注目されてきた.本論文では稠密重力データを最新の地震学的成果と結びつけ,東海~近畿地方におけるプレートの沈み込み帯での重力異常を調べた.地下深部構造とそこから期待されるブーゲ異常について細かく考察するために堆積物や海水の影響を取り去った.濃尾平野および近江盆地では,深層ボーリングデータにより基底までの深さと堆積層の密度を推定した.琵琶湖の湖水の影響についても湖底地形をコンタで与え,三次元タルワニ法で計算した.伊勢湾から太平洋にかけての海上・海底の重力データに対しては海底地形を与えて海水の補正を行なった.得られた修正ブーゲ異常図では琵琶湖付近に依然として負の領域が残り,その値は-40mGalに達することがわかった.この量をモホ面の起伏で説明すると中部山岳と同程度となる.この残差ブーゲ異常をフィリピン海プレートの沈み込みに関連づけて説明してみた.フィリピン海プレートの海洋地殻は玄武岩質のまま沈み込み,伊勢湾から若狭湾にかけて大陸地殻に接している.この海洋性地殻を含めたプレートの三次元モデルから計算したプレートの重力効果により,琵琶湖を中心とした負のブーゲ異常をうまく説明することができた.琵琶湖付近での残差ブーゲ異常はフィリピン海プレートの上部にある比較的軽い海洋地殻の浅いもぐりこみのために,見掛け上,地殻が厚くなることによって生ずると考えられる.これにより,(見掛け上)モホ面が深くなっていることも地殻底地震の震源面がせりあっていることもうまく説明できた.

著者

神沼 克伊 大滝 修 木村 勲

出版者

日本測地学会

雑誌

測地学会誌 (ISSN:00380830)

巻号頁・発行日

vol.43, no.4, pp.241-243, 1997-12-25 (Released:2010-09-07)

参考文献数

4

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A route for repeat leveling survey was established around Syowa Station (69° S, 39° E), East Ongul Island, Antarctica in 1979 and 1982. The leveling measurements were repeated in 1996. However only 2.3 km out of the total length of 5.3 km route was surveyed for the time limitation during the summer operation of the 37th Japanese Antarctic Research Expedition (DARE-37). The other part of the route was measured by DARE-38 in February 1997. In total, the discrepancy of forwardand backward leveling, and closing error of the measurement circuit, were obtained within the limitation of the first order leveling of the Geographical Survey Institute. However the measurement between BM 1029-BM 1030 was 0.6 mm out of the limitation. This was seemed to be caused by change of the field condition. There are two ponds named Midoriike and Kamome-ike between the two bench marks. Water overflowed from Kamome-ike to Midoriike during summer seasons in 1996 and 1997. Leveling survey had to be done in the water. This worst condition must be the reason of the measurement between BM 1029 and BM 1030 over the limitation. Except the results between BM 1029-BM 1030, no appreciable changes along the east-west direction (BM 1040-BM 1026) and the north-south direction (BM 1026-BM 1029) were observed for the last 15 years. It is inferred from geomorphological andgeophysical data that the crust around Syowa Station continues to uplift after deglaciation. The observations from repeat leveling measurements suggest no significant changes, which further supports the idea that the crustal uplift is a block movement. A route for repeat leveling survey was established around Syowa Station (69° S, 39° E), East Ongul Island, Antarctica in 1979 and 1982. The leveling measurements were repeated in 1996. However only 2.3 km out of the total length of 5.3 km route was surveyed for the time limitation during the summer operation of the 37th Japanese Antarctic Research Expedition (DARE-37). The other part of the route was measured by DARE-38 in February 1997. In total, the discrepancy of forwardand backward leveling, and closing error of the measurement circuit, were obtained within the limitation of the first order leveling of the Geographical Survey Institute. However the measurement between BM 1029-BM 1030 was 0.6 mm out of the limitation. This was seemed to be caused by change of the field condition. There are two ponds named Midoriike and Kamome-ike between the two bench marks. Water overflowed from Kamome-ike to Midoriike during summer seasons in 1996 and 1997. Leveling survey had to be done in the water. This worst condition must be the reason of the measurement between BM 1029 and BM 1030 over the limitation. Except the results between BM 1029-BM 1030, no appreciable changes along the east-west direction (BM 1040-BM 1026) and the north-south direction (BM 1026-BM 1029) were observed for the last 15 years. It is inferred from geomorphological and geophysical data that the crust around Syowa Station continues to uplift after deglaciation. The observations from repeat leveling measurements suggest no significant changes, which further sup-ports the idea that the crustal uplift is a block movement.