Eastern Olympus Mons Basal Scarp: Structural and mechanical evidence for large-scale slope instability

The expression of the Eastern Olympus Mons Basal Scarp (EOMBS) is seemingly unique along the edifice. It exhibits two slope-parallel structures: a nearly 100 km long upslope extensional normal fault system and a downslope contractional wrinkle ridge network, a combination that is found nowhere else on Olympus Mons. Through structural mapping and numerical modeling of slope stability of the EOMBS, we show that these structures are consistent with landsliding processes and volcanic spreading. The EOMBS is conditionally stable when the edifice contains pore fluid, and critically stable, or in failure, when the edifice contains a dipping overpressured confined aquifer and mechanical sublayer at depth. Failure of the fault-bounded portion of the flank results in estimated volumes of material ranging from 5600-6900 km(3), or 32-39% of the estimated volume of the "East" Olympus Mons aureole lobe. We suggest that the EOMBS faults may be an expression of early stage flank collapse and aureole lobe formation. Ages of deformed volcano adjacent plains associated with the wrinkle ridges indicate that this portion of the edifice may have been tectonically active at < 50 Ma and may be coeval with estimated ages of adjacent outflow channels, 25-40 Ma. This observation suggests that conditions that favor flank failure, such as water at depth below the edifice, existed in the relatively recent past and potentially could drive deformation to the present day.