HR: 14:55h
AN: T23D-05    [Abstracts]
TI: Investigating the Link Between Mantle Flow and Seismic Anisotropy in Regions of Subduction.
AU: * Pinero, L
EM: ear9ltp@earth.leeds.ac.uk
AF: University of Leeds, School of Earth and Environment, Leeds, LS2 9JT United Kingdom
AU: Kendall, J
EM: kendall@earth.leeds.ac.uk
AF: University of Leeds, School of Earth and Environment, Leeds, LS2 9JT United Kingdom
AU: Lowman, J
EM: j.lowman@earth.leeds.ac.uk
AF: University of Leeds, School of Earth and Environment, Leeds, LS2 9JT United Kingdom
AB: Plate subduction is a fundamental feature of mantle convection and observations of seismic anisotropy hold insights into the mantle's response to subduction. In general, observations of SKS splitting from subduction regions worldwide show considerable variability in both orientation and magnitude. Splitting in local events that sample the backarc show relatively small amounts of splitting and usually trench parallel orientations. Splitting in deeper slab events exhibit a behaviour more like that observed for SKS phases. Cumulatively, these observations suggest significant sub-lithospheric and sub-slab anisotropy. These observations have motivated geodynamical numerical modelling of thermal convection to investigate sub-lithospheric flow in subduction environments. In order to gain insights into the connection between mantle flow and seismic anisotropy we present calculations developed for 3D Cartesian-geometry models of mantle convection with rigid plates. The calculations incorporate a fixed plate geometry with velocities that evolve dynamically with the convecting system. A depth-dependent Newtonian viscosity and internal heating are included in the calculations. Wrap-around boundary conditions are imposed on the model. Simple 3D models that mimic Earth-like subduction settings show that the mantle flow field can be very complex and qualitatively explain the diversity of splitting measurements worldwide. Slab morphology and plate age severely affect the flow in near-slab regions and can induce slab-parallel flow. Thermal flow models are converted to heterogeneous anisostropic elastic models and shear-waves are tracked through the resulting subduction models. Synthetic splitting parameters are then compared with those from subduction regions around the world. The model results help explain the highly variable splitting parameters observed worldwide. In the past, trench parallel flow has been explained via more ad-hoc models where the mantle is forced to flow around the slab. Our modelling shows that trench-parallel fast shear-wave polarisations can be more simply explained by thermal effects.
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8158 Plate motions--present and recent (3040)
DE: 7200 SEISMOLOGY
DE: 7218 Lithosphere and upper mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting