AXIAL FOCUSING OF ENERGY FROM A HYPERVELOCITY IMPACT ON EARTH

We have performed computational simulations to determine how energy fr om a large hypervelocity impact on the Earth's surface would couple to its interior. Because of the first-order axial symmetry of both the i mpact energy source and the stress-wave velocity structure of the Eart h, a disproportionate amount of energy is dissipated along the axis de fined by the impact point and its antipode (point opposite the impact) . For a symmetric and homogeneous Earth model, all the impact energy t hat is radiated as seismic waves into the Earth at a given takeoff ang le (ray parameter), independent of azimuthal direction, is refocused ( minus attenuation) on the axis of symmetry, regardless of the number o f reflections and refractions it has experienced. Material on or near the axis of symmetry experiences more strain cycles with much greater amplitude than elsewhere, and therefore experiences more irreversible heating. The focusing is most intense in the upper mantle, within the asthenosphere, where seismic energy is most effectively converted to h eat. For a sufficiently energetic impact, this mechanism might generat e enough local heating to create an isostatic instability leading to u plift, possibly resulting in rifting, volcanism, or other rearrangemen t of the interior dynamics of the planet. These simulations demonstrat e how hypervelocity impact energy can be transported to the Earth's in terior, supporting the possibility of a causal link between large impa cts on Earth and major internally-driven geophysical processes.