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Seismological Study of 920km-mantle Discontinuity and the Mantle Transition Zone

Research Project

Project/Area Number 07640550
Research Category

Grant-in-Aid for Scientific Research (C)

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

Principal Investigator

KAWAKATSU Hitoshi  U.Tokyo, Earthquake Research Institute Associated Professor, 地震研究所, 助教授 (60242153)

Project Period (FY) 1995 – 1996
Project Status Completed (Fiscal Year 1996)
Budget Amount *help
¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 1996: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1995: ¥1,700,000 (Direct Cost: ¥1,700,000)
Keywordsmantle transition zone / 920km discontinuity / J-array / structure of earth's interior
Research Abstract

We have shown that certain features seismologically observable do exist in the mid-mantle beneath several subduction zones in the western ocean hemisphere.
By stacking hundreds of short-period seismograms observed in Japan ("J-array"), we have suggested that there is a seismic discontinuity at a depth of-920km beneath Tonga, Japan, and Indonesia subduction zones. Further study for Indonesia subduction zone, however, revealed a large depth variation of the discontinuty and thus we now cell it a "mid-mantle discontinuity". The depth variation of the mid-mantle discontinuity beneath the Indonesia arc, where the discontinuity deepens from 940 km at the eastern end to 1080 km at the western end, appears to be well correlated with the location of the high-velocity anomalies (HVA) in recent tomographic models. However, the mid-mantle discontinuity cannot be simply coincided with the bottom of the high-velocity anomalies as was suggested in our earlier paper as one possible explanation, because … More a velocity increase at the discontinuity is observed from the waveform analysis.
We utilized near receiver P-to-S conversion waves (so-called receiver function) to study the effect of the presence of a slab on the mantle transition zone discontinuities. Broadband waveforms of deep events occurred in Tonga observed at three stations in the northwestern ocean hemisphere, HIA,MDJ,MAJO,are stacked to produce receiver functions beneath those stations. Beneath the station in the northeast China (MDJ) where the subducted Pacific plate appears to stagnate along the '660-km' discontinuity, the discontinuity response function has more complicated features than those of other stations. The inversion result indcates no depression of the '660-km' discontinuity at the tip of the subducting slab beneath MDJ ; instead a multiple-discontinuity structure down to a depth of 780 km (at 670km, 740km and 780km) is observed. We interpret these features as the first in situ evidence for the garnet*ilemenite*perovskite phase transformation, as well as for gamma-spinel*perovskite+ Mg- wustite transformation. Less

Report

(3 results)
  • 1996 Annual Research Report   Final Research Report Summary
  • 1995 Annual Research Report
  • Research Products

    (11 results)

All Other

All Publications (11 results)

  • [Publications] Niv and Kawakatsu: "Direct evidence of the undulation of the 660km discustinvity" Geophysical Research Letters. 22. 531-534 (1995)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1996 Final Research Report Summary
  • [Publications] Niv and Kawakatsu: "Complex structure of the mantle discontinuities at the tip of subducting slab beneath the northeast china" Journal of Physics of Earth. 44. 701-711 (1996)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1996 Final Research Report Summary
  • [Publications] Niv and Kawakatsu: "Depth vaviation of the mid-mantle seismic discontinuity" Geophysical Research Letters. 24. 429-432 (1997)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1996 Final Research Report Summary
  • [Publications] Niu, F., and H.Kawakatsu: "Direct evidence of the undulation of the 660-km discontinuity beneath Tonga : comparison of Japan and US regional array data Geophys." Res.Lett.22. 531-534 (1995)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1996 Final Research Report Summary
  • [Publications] Niu, F., and H.Kawakatsu: "Complex structure of the mantle discontinuities at the tip of the subducting slab beneath the northeast China : a preliminary investigation of broadband receiver functions" J.Phys.Earth. 44. 701-711 (1996)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1996 Final Research Report Summary
  • [Publications] Niu, F., and H.Kawakatsu: "Depth variation of the mid-mantle seismic discontinuity, Geophys." Res.Lett.24. 429-432 (1997)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1996 Final Research Report Summary
  • [Publications] Niu and Kawakatsu: "Direct evidence for the undulation of the 660-km discontinuity beneath Tonga:Comparison of Japan and California array data" Geophysical Research Letters. 22. 531-534 (1995)

    • Related Report
      1996 Annual Research Report
  • [Publications] Niv and Kawakatsu: "Complex structure of the mantle discontinuities at the tip of the subducting slab beneath the northeast china" Journal of Physics of the Earth. 44. 701-711 (1996)

    • Related Report
      1996 Annual Research Report
  • [Publications] Niv and Kawakatsu: "Depth variation of the mid-mantle seismic discontinuity" Geophysical Research Letters. 24. 429-432 (1997)

    • Related Report
      1996 Annual Research Report
  • [Publications] Niu and Kawakatsu: "Direct evidence for the undulation of the 660-km discontinuity beneath Tonga:Comparison of Japan and California array data" Geophysical Research Letters. 22. 531-534 (1995)

    • Related Report
      1995 Annual Research Report
  • [Publications] Niu and Kawakatsu: "Complex structure of the mantle discontinuities at the tip of the subducting slab beneath the northeast China:a preliminary" Jourral of Physics of the Earth. 44. (1996)

    • Related Report
      1995 Annual Research Report

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Published: 1995-04-01   Modified: 2016-04-21  

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