Abstract P.I.: Humphreys Proposal Number: 97-11808 Institution: University of Oregon Title: Finite element modeling of the seismic and permeability properties of partially molten upper mantle The frequency dependent seismic response of partially molten upper mantle rock is to be determined using viscoelastic finite element computer simulations. Analytic solutions for the mechanical properties of this two-phase material have been elusive because of the complexity of the inclusion shapes. The finite element meshes are based on images produced from analysis of laboratory produced partially molten peridotites. To investigate S-waves, the mesh is strained with a step function in simple shear as a boundary condition and time is stepped forward allowing stress to decay as the melt flows and relaxes viscously. From this stress decay function the frequency dependent complex elastic moduli are computed, yielding the frequency dependent seismic velocity and attenuation. The method is benchmarked by comparing finite element results to relatively simple cases with known analytic solution (e.g., ellipsoids and triple junction tubule-shaped inclusions). Permeability is modeled by applying a pressure differential across the meshed sample, and calculating the hydraulic conductivity of the network from the bulk fluid transport.
