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Influence of buried craters on wrinkle ridges on Mars

Influence of buried craters on wrinkle ridges on Mars. Erwan Mazarico 12.521 Final Project. MOLA. Outline. Motivation Wrinkle Ridges on Mars Observations of Buried craters Modeling with Abaqus Preliminary Results Conclusion and Future Work. Motivation. Wrinkle ridges

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Influence of buried craters on wrinkle ridges on Mars

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  1. Influence of buried craters on wrinkleridges on Mars Erwan Mazarico 12.521 Final Project MOLA

  2. Outline • Motivation • Wrinkle Ridges on Mars • Observations of Buried craters • Modeling with Abaqus • Preliminary Results • Conclusion and Future Work

  3. Motivation • Wrinkle ridges • Globally observed • Compressional features • On volcanic plains, some “ghost craters” are observed Hypothesis = buried craters that influences the distribution of stresses at the surface of the volcanic layer

  4. Wrinkle Ridges • Topographic observations • Maximum relief of several 100’s meters • Spacing ~20-35km Solis Planum Lunae Planum Watters(2004)

  5. Wrinkle formation • Several scenarios • Single blind listric thrust fault • Thermal stresses • Multiple folds/faults (thrust, back-thrust) Montési and Zuber (2003)

  6. Single blind listric thrust fault Coulomb Watters (2004)

  7. Single blind listric thrust fault • Listric fault does not break the surface • Quite sensitive to fault geometry and slip • Thin-skinned formation • Consistent with buried craters localizing the thrust faults Coulomb

  8. Thermal Stresses • Thermal stresses due to global cooling are large • Compressional mechanism to form wrinkle ridges far from obvious loading/uplift zones • Shallow expression because elastic tensional stresses at greater depth • Explains ‘globality’

  9. Deep thrust faults • Large-scale topographic gradient on top of ridges • Large, deep (4-15km) thrust faults(<30°) • Near surface: fault stops; spay into smaller forward- or back-thrusts; accommodated by folding Golombek et al. (2001) Montési and Zuber (2003) Montési and Zuber (2003)

  10. Ghost Crater Example

  11. Ghost Crater • Formation Hypothesis Cartoon initial length

  12. Ghost Crater • Formation Hypothesis Cartoon initial length initial length

  13. Modeling with Abaqus • High-end FEM code with GUI, automatic meshing, etc. • Constructing the model and putting the BC • Different geometries tested • Crater modeled as cylinder, smooth cylinder, part of a sphere • Different displacements applied • Pushing on the X+ face, or both X-/X+ faces

  14. Using Abaqus Model Material •  = 0.6 •  = 0.25 • E = 20GPa •  = 2700 kg.m-3 176km x 176km x 25km

  15. Using Abaqus Mesh Tetrahedral elements

  16. Using Abaqus Boundary Conditions

  17. Using Abaqus Gravity Load

  18. Using Abaqus Impose displacement

  19. Abaqus Rheology Test Xtotal=19km=12.5% Elastic (  = 0.25 ) Elasto-Plastic Associated V≈9% V≈30.5% !! V≈2% V≈0% Elasto-Plastic Non-Associated Elastic Incompressible(  = 0.5 )

  20. Abaqus Rheology Test • Elastic is definitely not the rheology to use in our case • Elasto-Plastic Associated (EPA) causes some concern from the test … • Elasto-Plastic Non-Associated (EPNA) often crashes due to non-uniqueness (negative eigenvalues), or too high local plastic strains ►most runs are done in EPA

  21. Abaqus Results • Cylindrical crater • Cylindrical crater with smoothed edges • Spherical crater

  22. Cylindrical crater von Mises stresses

  23. Cylindrical crater Vertical displacement

  24. Cylindrical Crater Vertical displacement

  25. Cylindrical Crater Vertical displacement

  26. Cylindrical Crater AC Yield

  27. Smoothed Cylindrical Crater Vertical displacement

  28. Smoothed Cylindrical Crater Plastic Strain

  29. Spherical Crater Vertical Displacement

  30. Spherical Crater Total Strain

  31. Spherical Crater Concern AC Yield

  32. Problems encountered • Strange behavior of Elasto-Plasticity Associated material … (V, AC Yield) • Could not produce real wrinkles • Volcanic plain not superimposed (attempted but not successful)

  33. (very) preliminary conclusions • Localization of uplift at the crater rims seems to happen but needs futher work to be conclusive, especially after adding a layer above • Hard to form wrinkles and to use Abaqus properly !

  34. Future Work • Model crater with top layer (2-8km thick) with appropriate contact interaction • Use Abaqus output stresses to produce model of faults • Use 3d-def to get surface displacements • See conditions to have visible wrinkles following the buried craters • Count ghost craters from MOLA and see if consistent

  35. Thank you

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