S. Widiyantoro et al., Seismic tomography with P and S data reveals lateral variations in the rigidity of deep slabs, EARTH PLAN, 173(1-2), 1999, pp. 91-100
Regional seismic tomography of the northwest Pacific island arcs using P- a
nd S-wave arrival time data with similar path coverage reveals an oceanic l
ithospheric slab deflected in the mantle transition zone beneath the Izu Bo
nin region in good agreement with the results of earlier tomographic and ot
her seismic studies in the region. The S-wave images, however, do not show
clearly the deflection of the slab. This implies that the stagnant lithosph
eric slab in the transition zone is more likely a bulk-sound structure, whi
ch is strongly supported by our results from joint inversions for bulk-soun
d and shear wavespeeds. For the Izu Bonin region, where trench migration ha
s been reported, the properties of the deflected slab lying on top of the 6
60 km discontinuity show strong bulk-sound and weak shear signatures in con
trast to the descending slab itself. There is an indication in the shear im
ages that a component of the former oceanic lithosphere is penetrating into
the top of the lower mantle, suggesting that a slab split has occurred. (C
) 1999 Elsevier Science B.V. All rights reserved.