|Low Velocity Province at
Province at the CMB
Extent of the Pacific Low Velocity Province
Constrained by the Vietnam Broadband Seismograph Array
Figure: (a) Observed ScS-S and sScS-sS travel time residuals
projected at the bouncing points of ScS or sScS. (b) Synthetic ScS-S and
sScS-sS travel time residuals computed for our preferred model.
We present evidence showing the extent of the low-velocity region in the
lowermost mantle beneath the western Pacific. We analyzed S, sS, ScS-S,
and sScS-sS travel times
observed by the Vietnam broadband seismograph array deployed as part of
the Ocean Hemisphere Project. The abrupt changes in ScS-S and sScS-sS
travel times suggest that the western geographical boundary of the
low-velocity region is located around 140^\circ E and is sharp
(more than 4 % velocity contrast within 200 km; Figure).
The dependency of S and sS travel time anomalies of epicentral distances
suggests that the strong low-velocity region is confined to within 400 km
from the CMB (core-mantle boundary). The existence of lateral
with a 100 km scale inside the low-velocity region is also suggested by the
abrupt changes in S and ScS waveforms.
- Takeuchi, N., Morita, Y., Xuyen, N.D. & Zung, N.Q.,
2008. Extent of the low-velocity region in the lowermost mantle beneath the
western Pacific detected by the Vietnamese broadband seismograph array,
Geophys. Res. Lett., 35, L05307, doi:10.1029/2008GL033197.