Seismological evidence for compositional variations at the base of the mantle transition zone under Japan Islands

Akira Yamada, Dapeng Zhao, Toru Inoue, Daisuke Suetsugu, Masayuki Obayashi

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

Temperature and water content anomalies just above the 660-km discontinuity under the Japan Islands are estimated from seismological observations. Two sets of seismological observations of P-wave velocity perturbations and depth variations of the 660-km discontinuity are used, which are (1) long-wavelength (~ 500 km) variations from seismic tomography based on a grid parameterization and waveform analysis of ScS reverberations and (2) moderate-wavelength (~ 150 km) variations from seismic tomography with a block parameterization and receiver-function analysis. To estimate temperature and water content anomalies, partial derivatives of velocity and depth variations with respect to temperature and water content determined by mineral physics studies are used. Under Southwest Japan, low temperature and high water-content anomalies are obtained from both sets of seismological observations, which have already been found by a previous study. Under Northeast Japan, however, there are discrepancies between the results estimated from the two data sets, possibly due to the different resolution scales. This discrepancy is dismissed when examining distributions of the temperature and water content anomalies. These anomalies can be grouped into two geographical locations, one group under Southwest Japan, the other under Northeast Japan. The two groups are clearly separated and exhibit common features in both sets of the seismological observations. The grouping is interpreted by a compositional difference between the subducting Pacific slab under Southwest Japan and a normal mantle under Northeast Japan.

Original languageEnglish
Pages (from-to)482-490
Number of pages9
JournalGondwana Research
Volume16
Issue number3-4
DOIs
Publication statusPublished - 2009 Dec

Keywords

  • Mantle transition zone
  • Seismic observations
  • Subducting slab
  • Temperature anomaly
  • Water content

ASJC Scopus subject areas

  • Geology

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