Seismic evidence for high pore pressures in the oceanic crust: Implications for fluid-related embrittlement

Takahiro Shiina, Junichi Nakajima, Toru Matsuzawa

Research output: Contribution to journalArticlepeer-review

38 Citations (Scopus)


We estimated the P wave velocity structure of the crust of the subducting Pacific plate beneath northeast Japan using arrival time data of P-to-S-converted waves. The results show that the P wave velocity of the subducting crust varies along the arc and increases abruptly at a depth of ∼100 km, from 6.5-7.0 km/s in the fore arc to 7.5-8.5 km/s in the back arc. The P wave velocity in the fore arc is ∼10% lower than theoretically expected values for the metamorphosed mid-ocean ridge basalt material. Seismicity in the subducting crust is most active at depths of 70-80 km where P wave velocities are lowest. The marked reduction of P wave velocity suggests the coexistence of aqueous fluids with hydrous minerals. Abundant fluids elevate pore fluid pressures and reduce effective normal stress, promoting intensive seismic activity in the low-velocity crust. Our observations provide seismic evidence that earthquakes in the subducting crust are facilitated by fluid-related embrittlement.

Original languageEnglish
Pages (from-to)2006-2010
Number of pages5
JournalGeophysical Research Letters
Issue number10
Publication statusPublished - 2013 May 28


  • PS-converted wave
  • Pacific plate
  • dehydration
  • oceanic crust
  • seismicity
  • tomography

ASJC Scopus subject areas

  • Geophysics
  • Earth and Planetary Sciences(all)


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