HR: 17:30h
AN: U34A-07    [Abstracts]
TI: Testing Mantle Flow Models with Joint Seismic-Geodynamic Inversions
AU: * Simmons, N A
EM: nathan@geo.utexas.edu
AF: Jackson School of Geosciences,University of Texas at Austin, 1 University Station C1140, Austin, TX 78712
AU: Grand, S P
EM: steveg@geo.utexas.edu
AF: Jackson School of Geosciences,University of Texas at Austin, 1 University Station C1140, Austin, TX 78712
AU: Forte, A M
EM: forte.alessandro@uquam.ca
AF: Universitie de Quebec a Montreal, GEOTOP - Dept des Sciences de la Terre Universite de Quebec a Montreal, C. P. 888, Succ. Centre-Ville, Montreal, QUE h3c3p8 Canada
AB: Fundamental questions remain regarding the means by which the Earth's mantle convects. Three-dimensional seismic velocity models are instantaneous snapshots of the deep interior and should yield important information about the type of convection that occurs. However, these models have irregular resolution within them which changes amongst different models due to several factors including variation of datasets and methodology. Furthermore, the interpretation of the tomography models remains debatable. Seismic tomography models continue to improve over time; however, it is likely that their interpretation in terms of mantle layering will continue to be debated. Global gravity anomalies, dynamic surface topography, and plate motions are other surface observables that contain mantle flow signatures. With a density and viscosity field, these observables can be predicted in a forward model sense via dynamic response functions. Dynamic response functions relate a given density anomaly to a given geophysical observable and depend on the existence of chemical or phase change boundaries that impede vertical mass transport across the mantle as well as the viscosity of the mantle. Consequently, we may discriminate amongst various flow models that may or may not contain barriers to mantle flow. Using various scalings between seismic velocity and density, we can jointly invert geodynamic and seismic data for seismic velocity. We present some joint 3-D shear-wave seismic velocity inversions with various flow model assumptions using optimized velocity to density scalings and viscosity structures. For the seismic data, we use Sn, sSn, ScSn, sScSn, SKS, and SKKS travel time residuals (n refers to multi-bounce waves such as SS) totaling over 44,000 measurements. We combine these data with free-air gravity, dynamic topography, plate motion, and dynamic ellipticity measurements to generate the joint models for given mantle flow model assumptions. We have determined that we can fit the seismic and geodynamic data equally well as the seismic data alone given a whole mantle flow assumption. However, with the assumption that a barrier to flow exists near the 660km depth range, an equal fit to the seismic data cannot be established with the current data and model parameters. We will also present results from other mantle flow assumptions including impedance to flow near 1000km and 2000km depth ranges as well as alternate velocity-density scalings. Along with mantle flow mechanics, these results will give us an indication of the likelihood that negative velocity-density scalings exist in the deepest mantle as has been proposed for the African anomaly.
DE: 8180 Tomography
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 7203 Body wave propagation
DE: 7207 Core and mantle
SC: Union [U]
MN: 2004 AGU Fall Meeting