Small Subsidence of the 660-km Discontinuity Beneath Japan
Probed By ScS Reverberations
Mamoru Kato, Mika Misawa, and Hitoshi Kawakatsu
Geophys. Res. Lett., in press, 2000
Abstract
We investigated layering structure in the mantle beneath
the Japan Islands using the {\it ScS} reverberation waveforms
of two recent large deep events in the northwest Pacific.
Broadband seismograms of these events recorded at two dense
networks, J-Array and FREESIA, show clear {\it ScS} reverberations.
Regional variation of the elastic and anelastic structure
of the mantle as well as properties of the major velocity
discontinuities are estimated by waveform modeling. The 660-km
discontinuity is the deepest in the region where the stagnant
subducting slab in the transition zone is tomographically imaged,
and the subsidence is of $\sim$10 km, smaller than previous
estimates with {\it SS} precursors. No significant elevation
is detected for the 410-km discontinuity.