An anisotropic viscous representation of Mohr-Coulomb failure for use is modelling coupled mantle-continent dynamics

Moresi, L. and Muhlhaus, H. (2003). An anisotropic viscous representation of Mohr-Coulomb failure for use is modelling coupled mantle-continent dynamics. In: 2003 Fall Meeting, American Geophysical Union, Supplement to EOS, Transactions. 2003 Fall Meeting, San Francisco, USA, (220-220). 7-13 December, 2003.

Author Moresi, L.
Muhlhaus, H.
Title of paper An anisotropic viscous representation of Mohr-Coulomb failure for use is modelling coupled mantle-continent dynamics
Conference name 2003 Fall Meeting
Conference location San Francisco, USA
Conference dates 7-13 December, 2003
Proceedings title 2003 Fall Meeting, American Geophysical Union, Supplement to EOS, Transactions
Place of Publication Washington DC, USA
Publisher American Geophysical Union
Publication Year 2003
Sub-type Other
Volume 84
Issue 46
Start page 220
End page 220
Total pages 1
Language eng
Abstract/Summary In mantle convection models it has become common to make use of a modified (pressure sensitive, Boussinesq) von Mises yield criterion to limit the maximum stress the lithosphere can support. This approach allows the viscous, cool thermal boundary layer to deform in a relatively plate-like mode even in a fully Eulerian representation. In large-scale models with embedded continental crust where the mobile boundary layer represents the oceanic lithosphere, the von Mises yield criterion for the oceans ensures that the continents experience a realistic broad-scale stress regime. In detailed models of crustal deformation it is, however, more appropriate to choose a Mohr-Coulomb yield criterion based upon the idea that frictional slip occurs on whichever one of many randomly oriented planes happens to be favorably oriented with respect to the stress field. As coupled crust/mantle models become more sophisticated it is important to be able to use whichever failure model is appropriate to a given part of the system. We have therefore developed a way to represent Mohr-Coulomb failure within a code which is suited to mantle convection problems coupled to large-scale crustal deformation. Our approach uses an orthotropic viscous rheology (a different viscosity for pure shear to that for simple shear) to define a prefered plane for slip to occur given the local stress field. The simple-shear viscosity and the deformation can then be iterated to ensure that the yield criterion is always satisfied. We again assume the Boussinesq approximation - neglecting any effect of dilatancy on the stress field. An additional criterion is required to ensure that deformation occurs along the plane aligned with maximum shear strain-rate rather than the perpendicular plane which is formally equivalent in any symmetric formulation. It is also important to allow strain-weakening of the material. The material should remember both the accumulated failure history and the direction of failure. We have included this capacity in a Lagrangian-Integration-point finite element code and will show a number of examples of extension and compression of a crustal block with a Mohr-Coulomb failure criterion, and comparisons between mantle convection models using the von Mises versus the Mohr-Coulomb yield criteria. The formulation itself is general and applies to 2D and 3D problems, although it is somewhat more complicated to identify the slip plane in 3D.
Subjects EX
260206 Earthquake Seismology
780104 Earth sciences
Q-Index Code EX
Additional Notes abstract #T31D-0864

Document type: Conference Paper
Collection: School of Earth Sciences Publications
 
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Created: Fri, 24 Aug 2007, 12:53:52 EST