Guided wave observations and evidence for the low-velocity subducting crust beneath Hokkaido, northern Japan Geofluid processes in subduction zones and mantle dynamics

Takahiro Shiina, Junichi Nakajima, Genti Toyokuni, Toru Matsuzawa

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

At the western side of the Hidaka Mountain range in Hokkaido, we identify a clear later phase in seismograms for earthquakes occurring at the uppermost part of the Pacific slab beneath the eastern Hokkaido. The later phase is observed after P-wave arrivals and has a larger amplitude than the P wave. In this study, we investigate the origin of the later phase from seismic wave observations and two-dimensional numerical modeling of wave fields and interpret it as a guided P wave propagating in the low-velocity subducting crust of the Pacific plate. In addition, the results of our numerical modeling suggest that the low-velocity subducting crust is in contact with a low-velocity material beneath the Hidaka Mountain range. Based on our interpretation for the later phase, we estimate P-wave velocity in the subducting crust beneath the eastern part of Hokkaido by using the differences in the later phase travel times and obtain velocities of 6.8 to 7.5 km/s at depths of 50 to 80 km. The obtained P-wave velocity is lower than the expected value based on fully hydrated mid-ocean ridge basalt (MORB) materials, suggesting that hydrous minerals are hosted in the subducting crust and aqueous fluids may co-exist down to depths of at least 80 km.

Original languageEnglish
Article number69
Journalearth, planets and space
Volume66
Issue number1
DOIs
Publication statusPublished - 2014 Dec

Keywords

  • Dehydration
  • Finite difference method
  • Guided wave
  • Hokkaido
  • Intermediate-depth earthquake
  • Pacific slab
  • Subducting crust

ASJC Scopus subject areas

  • Geology
  • Space and Planetary Science

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