HR: 0800h
AN: T11C-0727    [Abstracts]
TI: Faults induced by Slab Bending: A Consequence of Pressure-Dependent Plasticity Coupled with Dislocation Creep
AU: Gerya, T V
EM: taras.gerya@erdw.ethz.ch
AF: Swiss Federal Institute of Technology, Dept. of Earth Sciences, Zurich, 8093, Switzerland
AU: * Yuen, D A
EM: daveyuen@gmail.com
AF: University of Minnesota, Dept. of Geology and Geophysics, Minneapolis, MN 55455, United States
AU: Connolly, J A
EM: jamie@erdw.ethz.ch
AF: Swiss Federal Institute of Technology, Dept. of Earth Sciences, Zurich, 8093, Switzerland
AB: Modeling of slab bending is of crucial importance in geodynamics and earthquake hazard issues, since this process is always associated with subduction and is related to the structural and seismic features inside the slab at the trench area. Of special interest is bending-related faulting of the incoming plate creating a pervasive tectonic fabric that cuts across the crust, penetrating deep into the mantle. Faulting is active across the entire ocean trench slope, promoting hydration of the cold crust and upper mantle surrounding these deep active faults. The along-strike length and depth of penetration of these faults are also similar to the dimensions of the rupture area of intermediate-depth earthquakes. We performed systematic numerical modelling of spontaneous bending process of incoming plate during subduction. In the beginning of this experiment two plates of different ages are juxtaposed together along the transform fault with low plastic strength creating favorable conditions for spontaneous initiation of subduction and the concurrent slab bending. Deformation pattern in slab bending area is quite distinct: the top of the slab is subjected to intense plastic deformation with localized faults zones while the bottom of the slab is deformed in a ductile way by dislocation creep with enhancement of the deformation due to high stresses in the bending area. The plastic deformation and dislocation creep fields are, respectively, characterized by extension and compression in a horizontal direction. These two fields are clearly separated by the narrow non-deforming area in the core of the slab characterized by low deviatoric stresses. Results of our experiments suggest that in case of free surface condition atop the slab it can be easily bent by its own weight triggering spontaneous retreating subduction. The bending process is facilitated (i) by lowered pressure in the extension region favouring deep penetration of faults and (ii) by high stresses in the compression region resulting in local lowering of slab viscosity due to the power-law nature of dislocation creep. The large depth of penetration of localized faults (10-50 km) and their uniform preferential dip are caused by pressure-dependent rather then depth-dependent plasticity. On the other hand dislocation creep in the deep portion of the slab promote lateral narrowing of bending zone ,causing the appearance of slab bending faults within localized 100- 150 km wide area atop the slab.
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 3613 Subduction zone processes (1031, 3060, 8170, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting