HR: 10:35h
AN: MR22A-02    [Abstracts]
TI: Seismic Waveform Modeling of a Phase Change in the Lowermost Mantle Associated with Chemical and Thermal Heterogeneity
AU: * Cormier, V F
EM: vernon.cormier@uconn.edu
AF: University of Connecticut, Physics Department 2152 Hillside Road, Storrs, CT 06269-3046 United States
AB: Poor lateral coherence of seismic waves interacting with the lowermost mantle (D^" region) may be consistent with either the effects of constructive and destructive interference of waves scattered from distributed heterogeneity in D^" or the effects of topography on one or more discontinuities. Likewise the transverse isotropy inferred from S waves interacting with this region can be the result of long wavelength averaging of smaller scale heterogeneity or topography of one or more discontinuities or sharp transitions in D^" structure. To determine if any of these effects of small-scale fabric can significantly bias the interpretation of D^" structure by simple layered models, seismograms are synthesized by a pseudospectral method in models of D^" fabric and complex topography of a possible perovskite phase transition. Structures examined include a discontinuity with statistically described topography, spatially continuous heterogeneity, and bimodal models of heterogeneity containing either high velocity inclusions (solid-solid phase changes) or low velocity inclusions (partial melt). Numerical experiments show that (1) apparent S anisotropy can be produced from isotropic distributions of heterogeneity in the presence of vertical gradients and (2) that it is difficult to create observable narrow angle reflections from D^" discontinuities without the existence of large-scale 3-D structure. These results demonstrate that the seismic interpretation of D^" structure can be assisted by mineral physics if it can provide constraints on the fabric and spatial thermal spectrum of a chemically heterogeneous lower mantle.
UR: http://www.phys.uconn.edu/~cormier/fall2005agu
DE: 3909 Elasticity and anelasticity
DE: 7203 Body waves
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7290 Computational seismology
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005