Near and far-field hazards of asteroid impacts in oceans

摘要

Hazards resulting from asteroid ocean impacts were modelled using hydrocode simulations to examine the near-field effects including the initial formation and subsequent long range propagation of tsunami waves that can transport potentially damaging energy far from the impact site.Three-dimensional simulations of oblique impacts into deep water, with trajectory angles ranging from 27 degrees to 60 degrees above the horizontal, were performed with the Los Alamos Rage hydrocode. The simulations include atmospheric effects such as ablation and airbursts. These oblique impact simulations are performed in order to help determine whether there are additional dangers due to the obliquity of impact not covered by previous studies. The energy transferred to both the air blast wave and the water are calculated as well as the amount of sea water lofted into the upper atmosphere. Water crater sizes and subsequent surface elevation profiles, surface pressures, and depth-averaged mass fluxes within the water are prepared for use in far-field propagation studies. Like previous three-dimensional simulations, these simulations show that except at exceedingly shallow entry angles below those simulated here the resulting waves are roughly circular and that the initial waves and central jet oscillation are highly turbulent and dissipate a lot of the energy.Two-dimensional axisymmetric simulations of long range propagation of impact tsunami were performed using the Lawrence Livermore ALE3D hydrocode on the NASA Pleiades supercomputer. These simulations showed that impacts under 1 gigaton TNT equivalent into the deep ocean basins will create deep-water waves that undergo dispersion, whereas impacts onto continental shelves will create shallow-water waves that do not suffer dispersion. The simulations also showed that on the order of 1% of the kinetic energy of the impact is converted into the tsunami wave. This is an order of magnitude less than previous semi-empirical estimates of similar to 15% based on explosion test data and laboratory scale impacts.