Abstract - Volcano-related subsidence on Mars has various forms, two of which are the subject of this study. On a small scale, collapse calderas have commonly developed at the tops of volcanic edifices. On a larger scale, whole edifices and their underlying basements seem to have subsided via lithospheric flexure. Previous continuum-based numerical
simulations of each of these processes revealed a similar pattern of surface stress states. These stress states are
generally used in conjunction with Andersonian fault mechanics to predict the structures that should form at the
Martian surface in response to subsidence. For calderas, a central zone of reverse faulting and a peripheral zone
of normal faulting have been postulated and observed. For lithospheric flexure, the same zones were broadly
predicted, but with the addition of an intermediate zone of strike-slip faulting. The prediction of the intermediate
zone has been problematic, however, because associated strike-slip faults have not been observed in nature. We
report results from experimental models of caldera subsidence and lithospheric flexure, both of which produce
arrays of structures that broadly conform to those observed in nature. However, an intermediate zone of strikeslip
faulting predicted by Andersonian theory is, as in nature, not observed. Instead, this zone mainly comprises
oblique-reverse and oblique-normal faults; 'pure' strike-slip faults are rare. Overall, the structures observed in
analogue simulations of both subsidence types are more compatible with those predicted by 3D strain theory of
faulting, rather than Andersonian theory. Our study suggests that a fuller understanding and prediction of faulting
related to volcanic subsidence on Mars and other planets should therefore be guided by 3D strain theory.
Abstract of talk given to:
EGU General Assembly, Vienna, April 2010.