HR: 0800h
AN: T21C-0515    [Abstracts]
TI: Fluid-mechanical Representation of Plate Boundaries - Trench-Ridge System -
AU: * Takaku, M
EM: mtakaku@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, Uniersity of Tokyo, 1-1-1,Yayoi, Bunkyo-ku, 113-0032 Japan
AU: * Takaku, M
EM: mtakaku@eri.u-tokyo.ac.jp
AF: IFREE,Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-Cho, Yokosuka-city, 237-0061 Japan
AU: Fukao, Y
EM: fukao@jamstec.go.jp
AF: Earthquake Research Institute, Uniersity of Tokyo, 1-1-1,Yayoi, Bunkyo-ku, 113-0032 Japan
AU: Fukao, Y
EM: fukao@jamstec.go.jp
AF: IFREE,Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-Cho, Yokosuka-city, 237-0061 Japan
AB: Seismic tomography models have been used extensively to simulate mantle convection driven by density heterogeneity. Such simulation to date has been unsuccessful to reconcile itself with the most obvious convection-related phenomenon of plate motions. Here we present a theoretical framework for tomography-based convection modeling to include the plates as an integral part of the mantle convection. We model the lithosphere as a highly viscous, incompressible, Newtonian fluid layer and plate boundaries as faults across which tangential velocities are discontinuous. Fluid-mechanical expressions of such faults have their exact analogies in the seismic source representation theory and can be derived by referring to it. We test this idea against the simplest two-dimensional case with only trench and ridge as plate boundaries, and with only subducting slab as mass anomaly. We model ridge (trench) as the horizontal (vertical) tensile fault that comprises of a conjugate pair of 45-degree dip normal (reverse) faults extending over the entire thickness of the surface layer. The system comprises of three elementary convections, slab mass-driven convection, trench fault-driven convection and ridge fault-driven convection. Flow due to the slab excess mass imposes vertical tensile stress on trench, which is released by flow driven by trench faulting. This faulting converts efficiently the vertical tensile stress to the horizontal tensile stress, which can transmit to extreme distances through the surface viscous layer. This horizontal tensile stress is relieved by flow driven by ridge faulting. The three elementary convections are thus coupled through the stress minimum conditions at ridge and trench. The resultant coupled flow is very plate-like in the surface viscous layer. In this system the horizontal surface velocity depends little on the relative distance between the ridge and trench and depends mostly on the excess weight of the subducting slab. The horizontal speed can be compared to the actual plate velocities for a lithosphere-asthenosphere system with a viscosity ratio of more than 10**3. The system is operated on the whole in a state of minimal stress.
DE: 1213 Earth's interior: dynamics (1507, 7207, 7208, 8115, 8120)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8168 Stresses: general
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: Fall Meeting 2005