Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.p32c0562c&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #P32C-0562
Physics
5475 Tectonics (8149), 6225 Mars, 8010 Fractures And Faults, 8020 Mechanics, 8164 Stresses: Crust And Lithosphere
Scientific paper
Alba Patera is one of the most peculiar and outstretched volcanoes known in the Planetary System, measuring up to 2700 km across, with a relative elevation of 7 km. The edifice is constituted by a large shield volcano with flat apex of about 5 km elevation on which formed a younger 2 km high central cone. As reported from the Viking images, Alba Patera is characterised by numerous extensional fractures in predominantly north-south direction. These grabens curve around the summit at about 200 km distance, off-centre toward the east. Some similar structures but over a limited radial extent (i.e. Catenae) are observed at a further distance at the lower slope of the main shield. A few radial compressive features or wrinkle ridges have been also identified on the summit. Using the Finite Element code Tekton, we reconstructed the stress fields induced by deformation under volcanic load and/or subsurface forces with addition of a regional extensional stress from the Tharsis rise, paying heed to the effects of the used parameters and to the failure criterion. We show that 1) simulating the topographic load as vertical forces or pressures on an elastic plate of constant thickness neglects the internal deformation of the edifice itself and its contribution to the plate thickness, which may be, however, considerable for a thin plate. We added therefore the whole geometry of the edifice, that is the observed topography and the major portion that fills the plate subsidence, and introduced body forces. 2) The bisected shape of the volcano, mentioned above, results in a local zone of higher differential stresses on the flanks. We obtained three domains of fault-types, a) a region of thrust faults at the summit, b) followed by strike-slip faulting and c) surrounded by concentric normal faults, these with increasing distance from the load centre. The wideness of the fault domains, the positions and the amounts of stress difference maxima depend strongly on the thickness of the plate, the load size, the Young modulus and the particular shape of the load. We also demonstrate how the various fault-domains on the surface and through the edifice are modified by the addition of a regional extensional stress and/or subsurface forces.
Cailleau Beatrice
Janle Peteh
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