Effects of Planet Curvature and Crust on the Shock Pressure Field Around Impact Basins

Abstract

We investigate the effects of planetary curvature and the crust-mantle boundary on the shock pressure field around impact basins on Mars using acoustic ray path calculations and hydrocode simulations. Planet curvature and, to a lesser extent, increasing sound speed with depth shallow the zone of wave interference, where shock pressures decay rapidly to the surface. The depth to the interference zone boundary diverges from the flat surface solution for projectile-to-Mars radius ratios greater than ~1% (transient craters greater than ~300 km); the difference increases with distance from the impact point and projectile size. In hydrocode simulations (but not the simple ray path model), the presence of the crust-mantle boundary produces nearly vertical pressure contours in the crust. Around Hellas basin, demagnetization occurs at shock pressures between 1.1 (±0.2) and 3.4 (±0.7) GPa, where the range is due to the uncertainty in the transient crater diameter.