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1993 Fiscal Year Final Research Report Summary

A study of deep structure of volcanoes and crustal earthquakes by seismic observations

Research Project

Project/Area Number 04452061
Research Category

Grant-in-Aid for General Scientific Research (B)

Allocation TypeSingle-year Grants
Research Field 固体地球物理学
Research InstitutionTOHOKU UNIVERSITY

Principal Investigator

HASEGAWA Akira  東北大学, 理学部, 教授 (40004460)

Co-Investigator(Kenkyū-buntansha) MATSUMOTO Satoshi  東北大学, 理学部, 助手 (40221593)
HINO Ryota  東北大学, 理学部, 助手 (00241521)
UMINO Norihito  東北大学, 理学部, 助教授 (30004477)
MATSUZAWA Tohru  東北大学, 理学部, 助手 (20190449)
HORIUSHI Shigeki  東北大学, 理学部, 助教授 (00004490)
Project Period (FY) 1992 – 1993
Keywordscrustal earthquake / deep structure of volcano / seismic tomography / seismic velocity structure / S-wave reflector / seismicity
Research Abstract

Possible evidence for manmatic activity in the crust and the uppermost mantle beneath northern Japan has been obtained from seismic observations. Tomographic image of the 3-D seismic velocity structure clearly delineate low-velocity zones, which are continuously distributed from the upper crust just beneath active volcanoes to the upper mantle. They are inclined to the west and nearly parallel to the dip of the subducted oceanic plate. Exceptionally deep (22-40km), low-freqyebcy micro earthquakes have been found at 12 locations around the low-velocity zones beneath volcanoes, suggesting a close relation to the deep magmatic activity. At shallower depth (10-15km) in or around the low-velocity zones, there exist distinct S-wave reflectors. Observed amplitude spectral rations of reflected to direct S-wave show that the reflector has a strong velocity contrast to the surrounding medium and its thickness is in the order of 100m, which suggests that the reflector body is a thin layr filled with partially molten materials. A detailed seismicity study reveals that the cutoff depth for shallow crustal seismicity changes with location and becomes shallow beneath active volcanoes. These observations appear to shed some light on the state of magma at depths and its close relation to shallow seismic activity in subduction zones.

  • Research Products

    (10 results)

All Other

All Publications (10 results)

  • [Publications] 堀内茂木: "高密度アレイ爆破観測による1931年小国地震震源域周辺の地震波散乱体の分布" 地震. 46. 75-84 (1993)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] 河野俊夫: "1962年宮城県北部地震(M6.5)震源域における微小地震活動" 地震. 46. 85-93 (1993)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] A.Hasegawa: "Deep structure of arc volcanoes as inferred from seismic observations" Phil.Trans.Roy.Soc.London. 342. 167-178 (1993)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] A.Hasegawa: "Deep,low-frequency microearthquakes in or around seismic low-velocity zones beneath active volcanoes in northeastern Japan" Tectonophysics.

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] A.Hasegawa: "Seismic structure of the northeastern Japan convergent margin:a synthesis" J.Geophys.Res.

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] S.Horiuchi: "Seismic scatter distribution near focal area of the 1931 Oguni Earthquake, Iwate Prefecture, northeastern Japan, as derived from P coda wave observations of an explosion by a dense seismic array network." J.Seism. Soc. Japan. 46. 75-84 (1993)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] T.Kono: "Microearthquake activity in the focal area of 1962 Northern Miyagi Earthquake (M6.5)." J.Seism. Soc. Japan. 46. 85-93 (1993)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] A.Hasegawa: "Deep structure of arc volcanoes as inferred from seismic observations." Phil. Trans. Roy. Soc. London.342. 167-178 (1993)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] A.Hasegawa: "Deep, low-frequency microearthquakes in and around seismic low-velocity zones beneath active volcanoes in northeastern Japan." Tectonophysics. in press.

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] A.Hasegawa: "Seismic structure of the northeastern Japan convergent margin : a synthesis." J.Geophys. Res.in press.

    • Description
      「研究成果報告書概要(欧文)」より

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Published: 1995-03-27  

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