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Detection of background acoustic free oscillations and development of a theory of background free oscillations in the system of the solid Earth and the atmosphere

Research Project

Project/Area Number 13304034
Research Category

Grant-in-Aid for Scientific Research (A)

Allocation TypeSingle-year Grants
Section一般
Research Field 固体地球物理学
Research InstitutionThe University of Tokyo

Principal Investigator

FUKAO Yoshio  the University of Tokyo, Earthquake Research Institute, Professor, 地震研究所, 教授 (10022708)

Co-Investigator(Kenkyū-buntansha) WATADA Shingo  University of Tokyo, Earthquake Research Institute, Research associate, 地震研究所, 助手 (30301112)
SUDA Naoki  Hiroshima University, Graduate School of Science, Associate Professor, 理学研究科, 助教授 (10222069)
TAHIRA Makoto  Aichi University of Education, Graduate course of Science education, Professor, 教育学部, 教授 (80024008)
NISHIDA Kiwamu  The University of Tokyo, Earthquake Research Institute, Research associate, 地震研究所, 助手 (10345176)
KOBAYASHI Naoki  Tokyo Institute of Technology, Earth and Planetary Sciences, Research associate, 理学系研究科, 助手 (30272660)
Project Period (FY) 2001 – 2003
Project Status Completed (Fiscal Year 2003)
Budget Amount *help
¥51,480,000 (Direct Cost: ¥39,600,000、Indirect Cost: ¥11,880,000)
Fiscal Year 2003: ¥4,680,000 (Direct Cost: ¥3,600,000、Indirect Cost: ¥1,080,000)
Fiscal Year 2002: ¥17,680,000 (Direct Cost: ¥13,600,000、Indirect Cost: ¥4,080,000)
Fiscal Year 2001: ¥29,120,000 (Direct Cost: ¥22,400,000、Indirect Cost: ¥6,720,000)
KeywordsLone period infrasounds / Earth's background free oscillations / Observation of barometers / 地球自由振動 / 気圧計 / 観測システム / 気圧変動
Research Abstract

In an eventual aim to detect background long period acoustic waves in the atmosphere that have to be excited incessantly by the same sources as for background free oscillations of the solid Earth, we installed a cross array of barometers in a 10 km--wide university forest in central Honshu. The array has 28 micro--barometers employing quartz crystal resonator technology with a station spacing of about 500 m. We analyzed 1-second continuous sampling records in a time period from March 2002 to November 2003 to obtain one--dimensional frequency--wavenumber spectra and two-dimensional frequency--slowness spectra to detect three kinds of waves in the seismic band from 1 mHz to 0.5 Hz. We measured the dispersion curves of these waves with an assumption of stochastic stationary plane waves. The waves we detected are (1)background internal gravity waves traveling from northwest at frequencies from 1 to 5 mHz with a phase velocity of about 50 m/s, (2)background acoustic waves traveling from nor … More thwest at frequencies from 0.01 to 0.1 Hz with a frequency-dependent phase velocity of about 400 m/s at 0.1 Hz and about 1000 m/s at 0.01 Hz, and (3)microbaroms traveling from southeast at frequencies from 0.1 to 0.5 Hz with a phase velocity of about 350 m/s. Internal gravity waves (1) dominate over the random component of atmospheric turbulence in the relevant frequency range. At higher frequencies the random component with coherent length shorter than 500m is dominant. Background acoustic waves (2) show clear annual variation with maxima in winter. The annual variation and their incident azimuths suggest their possible origins in mountain regions. Microbaroms (3) are most likely to be excited by standing ocean waves in nearby coastal regions. The power spectra of these acoustic waves were compared to the seismic spectra obtained in the same university forest. Their spectral shapes are mutually similar and change commonly with variable weather conditions, indicating that the microbaroms and microseisms have their common origins. Less

Report

(4 results)
  • 2003 Annual Research Report   Final Research Report Summary
  • 2002 Annual Research Report
  • 2001 Annual Research Report
  • Research Products

    (13 results)

All Other

All Publications (13 results)

  • [Publications] Nawa, K.: "Sea level variation in seismic normal mode band observed with on-ice GPS and on-land SG at Syowa Station, Antarctica"Geophys.Res.Lett.. 30(7). 1402 (2003)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2003 Final Research Report Summary
  • [Publications] 名和一成: "地球自由振動帯域における潮位変動の影響-昭和基地の場合-"地球. 25(6). 440-444 (2003)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2003 Final Research Report Summary
  • [Publications] Nawa, K.: "Sea level variation in seismic normal mode band observed with on-ice GPS and on-land SG at Syowa Station, Antarctica"Geophys.Res.Lett. 30(7). 1402 (2003)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      2003 Final Research Report Summary
  • [Publications] Nawa, K.: "Sea level variation in seismic normal mode band at Syowa Station"Chikyuu. 25(6). 440-444 (2003)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      2003 Final Research Report Summary
  • [Publications] Nawa, K., N.Suda, S.Aoki, K.Shibuya, T.Sato, Y.Fukao: "Sea level variation in seismic normal mode band observed with on-ice GPS and on-land SG at Syowa Station, Antarctica."Geophys.Res.Lett.. 30(7). (2003)

    • Related Report
      2003 Annual Research Report
  • [Publications] 名和一成, 須田直樹: "地球自由振動帯域における潮位変動の影響-昭和基地の場合-"地球. 25(6). 440-444 (2003)

    • Related Report
      2003 Annual Research Report
  • [Publications] Fukao Y, Nishida K, Suda N, Nawa K, Kobayashi N: "A theory of the Earth's background free oscillations"JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH. 107・B9. 2203 (2002)

    • Related Report
      2002 Annual Research Report
  • [Publications] Nishida K, Kobayashi N, Fukao Y: "Origin of Earth's ground noise from 2 to 20 mHz"GEOPHYSICAL RESEARCH LETTERS. 29・20. 1413 (2002)

    • Related Report
      2002 Annual Research Report
  • [Publications] 田平 誠: "大気の温度構造とインフラソニック波の長距離伝播"超音波TECHNO, 第3巻. 3・10. 23-27 (2001)

    • Related Report
      2002 Annual Research Report
  • [Publications] Fukao, Y., K. Nishida et al.: "A Theory of the Earth's background free oscillations"H, Geophys. Res.. (in press). (2002)

    • Related Report
      2001 Annual Research Report
  • [Publications] Nishida, K., N. Kobayashi, Y. Fukao: "Origin of Earth's ground noise at 0.2-2 mHz"Geoplys. Res Lett.. (in press, highlighted). (2002)

    • Related Report
      2001 Annual Research Report
  • [Publications] 田平 誠: "大気の温度構造とインフラソニック波の長距離伝播"超音波TECHNO,第3巻. 3・10. 23-27 (2001)

    • Related Report
      2001 Annual Research Report
  • [Publications] 綿田 辰吾: "Free-Unixを用いた安価な自動微気圧データ計測・転送システムの開発"東京大学地震研究所技術報告. 6. 33-37 (2000)

    • Related Report
      2001 Annual Research Report

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Published: 2001-04-01   Modified: 2016-04-21  

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