HR: 0912h
AN: U11B-06    [Abstracts]
TI: Global slab structure from (P-wave) travel time tomography: neither layered nor whole mantle convection
AU: * Van der Hilst, R D
EM: hilst@mit.edu
AF: Massachusetts Institute of Technology, Earth, Atmospheric, and Planetary Sciences, Cambridge, MA 01742, United States
AU: Li, C
AF: Massachusetts Institute of Technology, Earth, Atmospheric, and Planetary Sciences, Cambridge, MA 01742, United States
AB: We comment on the fate of slabs of subducted lithosphere using a new global model of three dimensional (3-D) variations in mantle P-wave velocity. The model is parameterized by means of rectangular cells in latitude, longitude, and radius, the size of which adapts to sampling. The largest single data source is ISC-NEIC data reprocessed by Engdahl and co-workers, from which we use routinely picked, short period P, Pg, Pn, pP and pwP data (for earthquakes between 1964-2004). Resolution in the lowermost and uppermost mantle is improved by differential times of core phases (PKPDF - PKPAB, PKPBC - PKPAB, Pdiff - PKPDF) and surface reflected waves (PP-P), respectively. The low frequency differential times (Pdiff, PP) are measured by waveform cross-correlation. Approximate 3-D finite frequency kernels are used to integrate the long period data (Pdiff, PP) and short period (P, pP, PKP) data. Spatial resolution is ~100 km in best sampled upper mantle regions. Our model reveals in unprecedented detail the rich variation in style of subduction of lithospheric slabs into the mantle. The images confirm the structural complexity of downwellings in the transition zone discussed in previous papers (Van der Hilst et al., Nature, 1991, 1995, 1997). Slab deflection is apparent in the transition zone beneath back arc regions in the western Pacific and the Mediterranean (Fukao et al., Rev. Geophys., 2001), but deeper penetration seems to occur beneath many other convergent margins, in particular Indonesia and the eastern Pacific/Americas (e.g., Ren et al., JGR, 2007). Owing to added data from stations in China, our model reveals with more clarity the structure of slab fragments stagnant in the transition zone beneath East Asia. As we have suggested before, these results of variable depth subduction are not consistent with the canonical models of either strict layering at 660 km depth or unhindered whole mantle convection.
DE: 7203 Body waves
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 7270 Tomography (6982, 8180)
SC: Union [U]
MN: 2007 Fall Meeting