3D modeling of planetary lobate scarps: The case of Ogygis Rupes, Mars

Abstract

Lobate scarps are the topographic expression of the largest thrust faults observed on the surfaces of terrestrial planets and their study provides information on the mechanical characteristics of the lithosphere at the time of formation. Here we show the results of 3D modeling of Ogygis Rupes, located in Aonia Terra, which is one of the most topographically pronounced lobate scarps described in the cratered martian highlands. The observed relief of Ogygis Rupes has been modeled by a combination of Trishear and Fault Parallel Flow algorithms, providing a successful reproduction of the observed topography through a 3D modeling that includes the main thrust fault, forming the lobate scarp relief, and two subsidiary backthrusts. This recreation allows us to interpret Ogygis Rupes relief, modeling the fault propagation folding, and constraining fault parameters and their variations along strike. The detailed slip distribution along the three faults reflects a general decay from the center to the edges for each fault, with the maximum slip value (2850 m) located approximately at the center of the main fault. The fault surfaces obtained for the main thrust fault and the two backthrusts show listric geometries at depth. The decollement where the main fault roots is set at ∼17–18 km deep, related to a main rheological threshold that on Mars is interpreted to be the depth of the Brittle-Ductile Transition at the time of the lobate scarp formation (Late Noachian/Early Hesperian). The listric morphology of the main fault implies that the total slip associated with this thrust fault is transmitted from the decollement, being representative of the regional shortening associated with the lobate scarp formation. Otherwise, the modeled backthrusts are subsidiary listric faults rooting at shallower depths (2.3–5.6 km), probably indicating the presence of mechanical discontinuities in the brittle domain of the martian lithosphere.