Marine Ecosystems Research Department - jamstec japan agency ...

Japan Marine Science and Technology Center
Institute for Frontier Research on Earth Evolution (IFREE)
estimate the thermal and chemical anomalies, we determined
mantle discontinuity depths using semi-broadband
waveform data from the Trans-Philippine Sea
Array. We employed Velocity Spectrum Stacking of the
receiver functions. First, we computed receiver functions
from three-component seismograms for each
event-station pair. After discarding the receiver functions
with low S/N ratios, we divided the receiver functions
into three groups, those at stations in the Mariana
Trough, in the Parece Vera Basin, and in the Daito
Ridge. We then stacked the receiver functions to
enhance the Pds converted signals from the mantle discontinuities,
where 'd' denotes a discontinuity depth. We
measured Pds-P times to determine the discontinuity
depths, taking into account the S-velocity structure
above the discontinuities, which was taken from existing
tomographic models. The discontinuity depths thus
determined are: km for "" and km
for "" beneath the Mariana Trough, km for
"" and km for "" beneath the Parece Vera
Basin, and km for "" beneath the Daito
Ridge. Signals from the "" were not detected
beneath the Daito Ridge (Fig.). The "" discontinuity
depths beneath the Philippine Sea are substantially
deeper than the global average (km). We will inter-
Fig.2 Lateral variations in Rayleigh wave phase velocities. Blue
lines denote higher velocities than average and red ones
lower velocities.
2.3. Depths of the mantle discontinuities beneath
the Philippine Sea using semi-broadband data
from the Trans-Philippine Sea Array
Studies of the depths of the "km" and "km"
mantle discontinuities indicate thermal and chemical
anomalies in the mantle transition zone independently of
tomographic studies. Recent seismic tomography studies
indicate that the Pacific slab is stagnant in the mantle
transition zone, which could impart thermal and/or
chemical anomalies in and around the stagnant slab. To
Fig. 3 Depths of the "410" and "660" and the thickness of the
mantle transition zone beneath the Philippine Sea. Green
triangles are the OBS stations and the red cross denote
the conversion points of P660s.
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