海半球ネットワーク:地球内部を覗く新しい目

2001 年度 実績報告書

• 研究課題/領域番号: 09NP1101
• 研究機関: 東京大学
• 研究代表者: 深尾 良夫 東京大学, 地震研究所, 教授 (10022708)
• 研究分担者: 浜野 洋三 東京大学, 大学院・理学系研究科, 教授 (90011709) ; 金沢 敏彦 東京大学, 地震研究所, 教授 (30114698) ; 山田 功夫 名古屋大学, 大学院・理学研究科, 教授 (60022670) ; 佐藤 忠弘 国立天文台, 助教授 (10000176) ; 藤本 博巳 東北大学, 大学院・理学研究科, 教授 (50107455)
• キーワード: 地震 / 地球観測 / 地球電磁気 / 測地 / 地球・惑星内部構造 / プレート運動 / 海底長期観測 / 西太平洋

研究概要

「海半球ネットワーク」計画最終年度にあたって、ネットワークを最終的に整備し、データの解析から大きな成果を得た。ネットワークの建設で特筆すべきは、海底掘削点利用の広帯域地震観測点を予定通り3点完成し、世界で初めて海底掘削点を含む海域ネットワークを完成した点である。既に北西太平洋観測点(WP2)からは世界最長の海底広帯域地震計記録を回収し、そのS/Nの高さは実証済みである。それ以外にも陸域広帯域地震観測網、陸域電磁気観測網、海底電磁気観測網、GPS観測網、超伝導重力アレー、データセンターが完成し順調に稼動中である。また,研究期間中に海底広帯域地震および海底電磁気を組み合わせた「長期機動観測」という新しい観測技術を,世界に先駆けで開発し実用化した。この技術開発により固定観測網を補完してさらに一桁高い分解能で地球内部を詳しく調べるという,研究の今後進むべき方向の一つが明確に示された。問題はこうした観測網をどのように維持するかであり、この点は今も努力中である。データ解析の面でも著しい成果をあげており、特に地震学では(1)スタグナントスラブの概念の確立、(2)常時地球自由振動現象の発見、電磁気学では(3)核内トロイダル磁場とマントル不均質構造とのカップリングによる非双極子磁場生成の説明(4)グローバルスケールの3次元電気伝導度トモグラフィーの実施、測地学では(5)西太平洋プレート運動の詳細解明などが特筆される。

研究成果

• [文献書誌] Sugioka, H., Y.Fukao, T.Okamoto, K.Kanjo: "Detection of shallowest submarine seismicity by acoustic-coupled-shear waves"J.Geophys.Res.. 106. 13485-13499 (2001)
• [文献書誌] Fukao, Y., S.Widiyantoro, M.Obayashi: "Stagnant slabs in the upper and lower mantle transition region"Rev.Geophys.. 39. 291-323 (2001)
• [文献書誌] Fukao, Y., K.Nishida, N.Suda, K.Nawa, N.Kobayashi: "A theory of the Earth's background free oscillations"J.Geophys.Res.. (in press). (2001)
• [文献書誌] Gorvatov, A., Y.Fukao, S.Widiyantoro, E.Gordeev: "Seismic evidence for a mantle plume oceanward of the Kamchatka-Aleutian trench junction"Geophys.J.In., 146.. 146. 282-288 (2001)
• [文献書誌] Gorvatov, A., Y.Fukao, S.Widiyantoro: "Application of a three-dimensional ray-tracing techique to global P, PP and P diff travel time tomography"Geophys.J.Int.. (in press). (2001)
• [文献書誌] Nishida, K., N.Kobayashi, Y.Fukao: "Origin of Earth's ground noise at 0.2-2 mHz"Geophys.Res.Lett.,. (in press). (2001)
• [文献書誌] Takeuchi, N., S.Watada, S.Tsuboi, Y.Fukao, M.Kobayashi, Y.Matsuzaki, T.Nakamura: "Application of distribution distributed object technology to seismic waveform distribution"Seism.Res.Lett.,. (in press). (2001)
• [文献書誌] Iidaka, T., Niu, F: "Mantle and crust anisotropy in the eastren china ragion region as inferred from waveform splitting of SKS and PpSms"Earth, Planets and Space. 53. 159-168 (2001)
• [文献書誌] Iidaka, T., Niu, F: "Seismic anisotropy beneath the Lau back-arc basin inferred from sScS-ScS splitting data"Geophys.Res.Lett.. 28. 863-866 (2001)
• [文献書誌] Kato, M, M.Misawa, H.Kawakatsu: "Small Subsidence of the 660-km Discontinuity Beneath Japan Probed By ScS Reverberanons"Geophys.Res.Lett.,. 28. 447-450 (2001)
• [文献書誌] Kato, M, H.Kawakatsu: "Seismological in situ Estimation of Density Jumps across the Transition Zone Discontinuities beneath Japan"Geophys.Res.Lett.,. 28. 2541-2544 (2001)
• [文献書誌] Vinnik, L., M.Kato, H.Kawakatsu: "Search for seismic discontinuities in the lower mantle"Geophys.J.International,. 147. 41-56 (2001)
• [文献書誌] S.Tsuboi, M.Saito, Y.Ishihara: "Verification of horizontal-to-vertical spectral ratio technique for estimation of site response using borehole seismographs"Bulletin of Seismological Society of America. 91. 499-510 (2001)
• [文献書誌] S.Tsuboi, M.Saito: "Existence of finite rigidity layer at the base of the Earth's liquid outer core inferred from anomalous splitting of normal modes"Earth Planets Space. (in press). (2002)
• [文献書誌] Y.Fukao, Y.Morita, M.Shiobara, T.Kanazawa, H.Utada, H.Toh, T.Kato, T.Sato, H.Shiobara, N.Seama, H.Fujimoto, N.Takeuchi: "The Ocean Hemisphere Network Project (OHP)"Workshop Report OHP/ION Joint Symposium, "Long-Term Observations in the Oceans," Yamanashi, Jan.. 13-29 (2001)
• [文献書誌] N.Takeuchi, M.Kobayashi, R.J.Geller: "Whole mantle S wave structure obtained by preliminary broadband waveform inversion using the Direct Solution Method"OHP/ION Joint Symposium on "Long-Term Observations in the Oceans," Yamanashi, Jan.. 194-195 (2001)
• [文献書誌] N.Takeuchi, S.Watada, Y.Fukao, S.Tsuboi: "OHP data center"OHP/ION Joint Symposium on "Long-Term Observations in the Oceans", Yamanashi, Jan. 2001. 11-12 (2001)
• [文献書誌] H.Mizutani, R.J.Geller, N.Takeuchi: "Derivation of optimally accurate operators for computation of synthetic seismograms for a medium with internode discontinuities"OHP/ION Joint Symposium on "Long-Term Observations in the Oceans" Yamanashi, Jan. 2001. 209 (2001)
• [文献書誌] Chi, P.J., C.T.Russell, J.Raeder, E.Zesta, K.Yumoto, H.Kawano, K.Kitamura, S.M.Petrinec, V.Angelopoulos, G.Le, M.B.Moldwin: "Propagation of the preliminary reverse impulse of sudden commencements to low latitudes"J.Geophys.Res. 106. 18857-18864 (2001)
• [文献書誌] Kepko, L., M.G.Kivelson, K.Yumoto: "Flow bursts, braking, and Pi2 pulsations"J.Geophys.Res. 106. 1903-1915 (2001)
• [文献書誌] Waters, C.L., M.D.Sciffer, B.J.Fraser, F.W.Menk, K.Foulkes, K.Brand, O.Saka, K Yumoto: "The phase structure of very low latitude ULF waves across dawn"J.Geophys.Res.. 106. 15599-15607 (2001)
• [文献書誌] Foldvary L., Y.Fukuda: "IB and NIB Hypotheses and Their possible Discrimination by GRACE"Geophys.Res.Lett. 28. 663-666 (2001)
• [文献書誌] Foldvaxy L., Y.Fukuda: "Evaluation of Temporal Variations on the Gravity Field Caused by Geophysical Fluids and Their Possible Detection by GRACE"JAG Symposia. 123. 143-148 (2001)
• [文献書誌] Hatanaka, Y, A.Sengoku, T.Sato, J.M.Johnson, C.Rocken, C.Meertens: "Detection of Tidal Loading Signals from GPS Permanent Array of GSI Japan"J.Geodetic Soc.Japan. 47. 187-192 (2001)
• [文献書誌] Imanishi, Y.: "Development of a High-Rate and High-Resolution Data Acquisition System Based on a Real-Time Operating System"J.Geod.Soc.Japan. 47. 52-57 (2001)
• [文献書誌] Matsumoto, K., T.Sato, T.Takanezawa, M.Ooe: "A Program for Computation of Oceanic Loading Effects"J.Geodetic Soc.Japan. 47. 243-254 (2001)
• [文献書誌] Mukai, A., S.Takemoto, T.Higashi, Y.Fukuda: "Oceanic Tidal Loadings Estimated from Gravity Observations in Kyoto and Bandung"J.Geod.Soc.Japan. 47. 261-266 (2001)
• [文献書誌] Ogasawara, S., Higashi, T., Fukuda, Y., S.Takemoto: "Calibration of a Superconducting Gravimeter with an Absolute Gravimeter FG-5 in Kyoto"J.Geod.Soc.Jpn. 47. 404-409 (2001)
• [文献書誌] Sato, T., Asari, K., Tamura, Y., Plag, H.P., Digre, H., Fukuda, Y., Hinderer, J.Kaminuma, K., Y.Hamano: "Continuous Gravity Observation at Ny-Alesund, Svalbard, Norway with a Superconducting Gravimeter CT#039"J.Geod.Soc.Jpn. 47. 341-346 (2001)
• [文献書誌] Sato T., Y.Fukuda, Y.Aoyama, H.McQueen, K.Shibya, Y.Tamura, K.Asari, M.Ooe: "On the observed annual gravity variation and the effect of sea surface height variations"Phys.Earth Planet.Interiors. 123. 45-63 (2001)
• [文献書誌] Sudo, Y., L.S.L.Kong: "Three-dimensional seismic velocity structure beneath Aso Volcano Kyushu, Japan"Bull Volcanol. 63. 326-344 (2001)
• [文献書誌] SUN, H.-P., S.Takemoto, H.-T.Hsu, T.Higashi, A.Mukai: "Precise tidal gravity recorded with superconducting gravimeters at stations Wuhan (China) and Kyoto (Japan)"J.Geodesy. 74. 720-729 (2001)
• [文献書誌] Tanaka, Y., Okubo, S., Machida, M., Kimura, I., Kosuge, T: "First Detection of Absolute Gravity Change Caused by Earthquake"Geophys.Res.Lett. 28. 2979-2981 (2001)
• [文献書誌] Yamamoto, K., Ishihara, K., Okubo, S., Araya, A: "Accurate evaluation of ocean tide loading effects for gravity in nearshore region : the FG5 measurements at Sakurajima volcano in Kagoshima Bay, Japan"Geophys.Res.Lett. 28. 1807-1810 (2001)
• [文献書誌] Sumita, I., Hatakeyama, T., Yashihara, A., Hamano, Y: "Paleomagnetism of late Archean rocks of Hamersley basin, Western Australia and the paleointensity at early Proterozonic"Phys.Earth Planet.Int. 128. 223-241 (2001)
• [文献書誌] A.Namiki, K.Kurita: "The influence of boundary heterogeneity in experimental models of mantle convection internal heat sources"Phys.Eartli Planet.Inter. 128. 195-205 (2001)
• [文献書誌] Uyeshima, M., H.Utada, Y.Nishida: "Network-MT method and its first results in central and eastern Hokkaido"Geophys.J.Int.. 146. 1-19 (2001)
• [文献書誌] Palshin N.A., L.L.Vanyan, R.D.Medzhitov, G.I.Shapiro, M.A.Evdoshenko, H.Utada, H.Shimizu, Y.Tanaka: "Use of the Nakohdka-Naoetsu submarine cable the temporal variability of the integral water transport in the sea of Japan"Oceanology. 41. 447-453 (2001)
• [文献書誌] Zhao, G., J.Tang, H.Utada, M.Uyeshima, M.Ichiki M.Ma, Z.Huang, H.Wang: "Measurement of Network-MT in two areas of NE China for study of upper mantle conductivity structure of the back-arc region"Seismology and Geology. 23. 143-152 (2001)
• [文献書誌] Ichiki, M., Uyeshima, M., Utada, H., Zhao, G., Tang, J., Ma, M: "Upper mantle conductivity structure of the back-arc region beneath northeastern China"Geophys.Res.Lett. 28. 3773-3776 (2001)
• [文献書誌] Koyama, T., H.Shimizu, H.Utada: "Possible effects of lateral heterogeneity in the D" layer on electromagnetic variations of core origin"Phys.Earth Planet. Int. 129. 99-116 (2002)
• [文献書誌] Salisbury, M.H., Shinohara, M., Richter, C., et al.: "Galley Proof 1 March 2002"Proc.ODP, Iint.Repts.. 195(in press). (2002)
• [文献書誌] Sacks, I.S., Suyehiro, K., Acton, G.D., et al.: "Western Pacific Geophysical Observatories"Proc.ODP, Init.Repts.. 186. (2000)
• [文献書誌] Kanazawa, T., Sager, W.W., Escutia, C., et al.: "Northwest Pacific Seismic Observatory and Hammer Drill Tests"Proc.ODP, Init.Repts.. 191. 1-159 (2001)
• [文献書誌] Matsuzawa, T., T.Igarashi, A.Hasegawa: "Characteristic small-earthquake sequence off Sanriku, northeastern Honshu, Japan"Geophys.Res.Lett. (2002)
• [文献書誌] Matsuzawa, T., T.Igarashi, A.Hasegawa: "Regularly occurring small earthquakes off Sanriiku, Japan"Tohoku Geophys.J.. 36. 263 (2001)
• [文献書誌] Kensaku Tamaki, H.Fujimoto, Yuji Orihashi, Masao Nakanishi, Phillipe Huchon: "Hotspot-ridge interaction in the Gulf of aden, East aflica"Eos, Transactions, Amercan Geophysical Union, AGU2001 Fall Meeting. 82, (47), November. (2001)
• [文献書誌] Park, J-O., Tsuru, T., Hamajima, T., Kaneda, Y., Taira, A., Kuramoto, S., EW9907/08 Shipboard Scientific Party: "AVO Analysis Along the Nankai Trough Decollement"Journal of Geography. 110(4). 510-520 (2001)
• [文献書誌] Fujie, G., J.Kasahara, R.Hino, T.Sato, M.Shinohara, K.Suyehiro: "A significant relation between seismic activities and reflection intensities in the Japan Trench region"Geophys.Res.Lett.. (in press). (2002)
• [文献書誌] Zhao, D., K.Wang, G.Rogers, S.Peacock: "Tomographic image of low P velocity anomalies above slab in northern Cascadia subduction zone"Earth, Planets and Space. 53. 285-293 (2001)
• [文献書誌] Zhao, D., F.Ochi, E.Takahashi: "Seismic images of hot spots and mantle plumes"AGU Monograph : "Hawaiian Volcanoes : Deep underwater perspectives". Vol.128. 349-364 (2001)
• [文献書誌] Zhao, D.: "Seismological structure of subduction zones and its implications for arc magmatism and dynamics"Phys.Earth Planet.Inter.. 127. 197-214 (2001)
• [文献書誌] Zhao, D.: "New advances of seismic tomography and its applications to subduction zones and earthquake fault zones : A review"The Island Arc. 10. 68-84 (2001)
• [文献書誌] Zhao, D.: "Seismic structure and origin of hotspots and mantle plumes"Earth Planet.Sci.Lett. 192. 192 (2001)
• [文献書誌] 金沢敏彦, 篠原雅尚, 塩原肇, 望月将志, 荒木英一郎, 末広潔: "海半球ネットワークによる広帯域地震観測網"月刊地球. 23-1. 18-26 (2001)
• [文献書誌] 松澤暢, 五十嵐俊博, 長谷川昭: "小地震の解析からわかるプレート間固着状況の時空間変動"SEIMO. 5, No.10. 11-12 (2001)
• [文献書誌] Azusa S., T.Shibutani: "Upper mantle transition zone structure beneath h the Philippine Sea region"Geophys.Res.Lett.,. 28. 871-874 (2001)
• [文献書誌] 山田功夫: "STS-1型地震計の長期安定性に関する問題"地震. 53. 259-262 (2001)
• [文献書誌] 木股文昭: "東海地域で観測される地殻変動の時間ゆらぎとプレートカップリング,"月刊地球. 33. 126-138 (2001)
• [文献書誌] 田部井隆雄, 木股文昭, 大蔵啓弘, 加藤照之, 小竹美子: "GPS観測から見たフィリピン-インドネシア東部の地殻変動"月刊地球. 23. 71-75 (2001)
• [文献書誌] Furumoto, M., Y.Ichimori, N.Hayashi, Y.Hiramatsu, T.Satoh: "Seismic wave velocity changes and stress build-up in the crust of the Kanto-Tokai region"Geophy.Res.Lett.. 28. 3737-3740 (2001)
• [文献書誌] Yoshida M.: "Oscillation of a mountain root strucyure due to a Rayleigh wave incidence"Earth Planets Space. 53. 1009-1109 (2001)
• [文献書誌] 野原 肇, 木股文昭, 三輪 篤, 林 宏和, 平原和郎: "水蒸気ラジオメータ観測による名古屋上空の大気水蒸気分布-1999年10-11月"東濃地震科学研究所報告. 6. 85-90 (2001)