HR: 16:45h
AN: U44A-04 INVITED    [Abstracts]
TI: Inverse scattering of ScS and SKKS waves: high resolution, large scale imaging of Earth's core-mantle boundary region
AU: Wang, P
EM: wangp@mit.edu
AF: Massachusetts Institute of Technology, Earth, Atmospheric, and Planetary Sciences, Cambridge, MA 02139, United States
AU: * Van der Hilst, R D
EM: hilst@mit.edu
AF: Massachusetts Institute of Technology, Earth, Atmospheric, and Planetary Sciences, Cambridge, MA 02139, United States
AU: De Hoop, M V
AF: Purdue University, Center for Computational and Applied Mathematics, Purdue, IN 047907, United States
AU: Shim, S
AF: Massachusetts Institute of Technology, Earth, Atmospheric, and Planetary Sciences, Cambridge, MA 02139, United States
AB: With 3-D inverse scattering of broad band waves we have begun to explore the deep mantle on an unprecedented spatial scale. We combine concepts from inverse scattering (generalized Radon transform, or GRT) and statistics into an approach toward imaging structure near Earth's core-mantle boundary with large amounts of broad-band, three-component ScS and SKKS seismograms acquired by global seismograph networks. Extracting structural information requires few restrictive a priori assumptions about the structures of interest, which makes it complementary to forward modeling approaches. With a generalized Radon transform (GRT) we map broad-band seismogram windows -- comprising the main arrivals and its coda and precursors -- into images that reveal multiple, piece-wise continuous (and statistically significant) interfaces in the lowermost mantle. Tomographic wavespeed perturbations and the variation in depth to a widespread interface 150-300 km above the CMB are consistent with a post-perovskite (ppv) transformation. Stratification below it may results from multiple phase boundary crossings, and a locally observed wavespeed drop above the CMB may mark the base of a ppv-rich lens. We use thermodynamic properties of these phase transitions to estimate temperatures just above the core-mantle boundary (CMB). We infer a temperature at the CMB of 3,950±200 K. Beneath Central America, a site of deep subduction, the deep mantle is relatively cold (ΔT=700±100 K) and core heat flux high (qcmb=80-160 mWm-2, for thermal conductivity κ=5-10 Wm-1K-1). Away from it, the heat flux reduces to 35-70 mWm-2. GRT imaging with ScS can reveal D" structure beneath selected geographical regions (e.g., central and north America, north Pacific, east Asia), but sampling of underside SKKS reflections may allow hemisphere scale D" imaging.
DE: 0910 Data processing
DE: 7203 Body waves
DE: 7207 Core (1212, 1213, 8124)
DE: 7260 Theory
SC: Union [U]
MN: 2007 Fall Meeting