HR: 16:30h
AN: T14B-03    [Abstracts]
TI: Imaging structure at and near the core mantle boundary with a generalized Radon transform of broad band ScS and SKKS coda waves
AU: Wang, P
EM: wangp@mit.edu
AF: EAPS-MIT, 77 Masschusetts Ave, Cambridge, MA 02139 United States
AU: * Van der Hilst, R
EM: hilst@mit.edu
AF: EAPS-MIT, 77 Masschusetts Ave, Cambridge, MA 02139 United States
AU: De Hoop, M
EM: mdhoop@mines.edu
AF: CWP-CSM, Colorado School of Mines, Cambridge, CO 80401 United States
AU: Ma, P
EM: pingma@stat.harvard.edu
AF: Department of Statistics, Harvard University, Cambridge, MA 02138 United States
AB: Abstract: Seismic constraints on structure at or near the core-mantle boundary (CMB) and on the nature of any nearby interfaces is of great importance for understanding the mineralogy, phase chemistry, and dynamics in Earth's lowermost mantle. Much pioneering work has been done with forward modeling of core reflected or diffracted waves, but the exponentially growing data sets available through IRIS call for powerful inversion methods. In order to produce accurate images of scatterers or interfaces near the core-mantle boundary (CMB) from seismic body waves such as ScS and SKKS - and their codas - we have developed a generalized Radon transform (GRT) from 'exact' asymptotic analysis and the theory of Fourier integral operators. We enhance the images, estimate uncertainty, and infer scaling properties of the interfaces using mixed-model statistics (i.e., properties of the GRT imaging operator are used to describe and reduce noise and data misfit). Our inverse scattering approach is set up to process and interpret tens of thousands of broad-band waveforms in order to detect (and characterize) variations in acousto-elastic properties in the so-called D" region, the CMB proper, and Earth's outermost core. We present applications of GRT imaging to a selected region of the CMB beneath Central America; all ScS rays with a midpoint in this selected region (from -115 to -65W and -10S to 40N) and generated by earthquakes with an Mb magnitude larger than 5.2 are used. We hope to constrain the lateral variation in height above the CMB (related to the Clapeyron slope in case of a phase transition) and the regularity of interfaces in the bottom 300 km or so of the mantle. A pilot study, with over 20,000 ScS records, has yielded image gathers that reveal a sharp CMB and a more gradual interface ~ 280 km above it, and there are hints of structures in between. We will present results for a great circle transect from (-105W, 0) to (-75W, 30N): some 65,000 transverse component broad band records are used to construct 40 juxtaposed radial image gathers, which in combination form a 2000 km long 2-D profile of structure at or near the CMB beneath Central America.
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 7207 Core and mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting