川勝 均 氏　(地震研究所)

「Seismic Evidence for Deep Water Transportation in the Mantle」

2007年4月25日

Water in the mantle is expected to play essential roles in
various significant problems of geodynamics,
such as generation of the arc volcanism, lubrication of the
subduction zone plate interface, controlling mantle rheology, and
delineating its location and abundance in the
mantle may be considered as one of the most important issues
in the current earth science.
How water is transported into the mantle, however, has never
been clear, except that it is generally believed the subducting
hydrated oceanic crust is the major carrier.
I present seismic evidence indicating the transportation
of water into the deeper portion of the mantle
wedge of the subduction zone beneath northeastern Japan.
The reflectivity profiles of seismic waves obtained from
migrated receiver functions of teleseismic earthquakes
recorded by Hi-net show strong signature of the dehydration
of the subducting oceanic crust in the depth interval of 50-90km.
Below this depth range, a low-velocity layer on the top of
the subducting plate, which we infer as a channel
of serpentinite that brings water into the deep mantle,
is observed. The overall feature of our image
is consistent with the result of the numerical simulation of
the water transportation beneath the Japan arc by Iwamori (2007),
and thus provides a strong line of evidence for deep water
transportation within the mantle wedge of the subduction zone.