Anomalous deepening of a seismic belt in the upper-plane of the double seismic zone in the Pacific slab beneath the Hokkaido corner: Possible evidence for thermal shielding caused by subducted forearc crust materials

Saeko Kita, Tomomi Okada, Akira Hasegawa, Junichi Nakajima, Toru Matsuzawa

Research output: Contribution to journalArticlepeer-review

96 Citations (Scopus)

Abstract

Hypocenter relocations of earthquakes in the Pacific slab have shown an anomalous deepening of a seismic belt in the upper-plane of the double seismic zone at depths of 80-120 km beneath the Hokkaido corner, while it is located at depths of 70-90 km in the surrounding Tohoku and eastern Hokkaido areas. Seismic tomographic inversions performed beneath the Hokkaido corner have shown that a low-velocity zone having seismic velocities of crust materials exists in the mantle wedge just above the Pacific slab and makes direct contact with the upper surface of the Pacific slab. These observations suggest that: 1) the low-velocity zone just above the Pacific slab is part of the subducted Kuril forearc sliver. 2) The contact with the subducted, and so relatively cold, sliver materials prevents the mantle wedge from heating the Pacific slab and causes a lower temperature condition in the Pacific slab crust beneath the Hokkaido corner than in the surrounding areas. 3) As a result, a delay of eclogite-forming phase transformations occurs and enhances the local deepening of the seismic belt in the slab crust there.

Original languageEnglish
Pages (from-to)415-426
Number of pages12
JournalEarth and Planetary Science Letters
Volume290
Issue number3-4
DOIs
Publication statusPublished - 2010 Feb 20

Keywords

  • Hokkaido corner
  • dehydration embrittlement
  • eclogite-forming phase transformation
  • intraslab earthquakes
  • the upper-plane seismic belt

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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