Antipodal focusing of seismic waves due to large meteorite impacts on Earth

SUMMARY

We examine focusing of seismic waves at the antipode of large terrestrial meteorite impacts, using the Chicxulub impact as our case study. Numerical simulations are based on a spectral-element method, representing the impact as a Gaussian force in time and space. Simulating the impact as a point source at the surface of a spherically symmetric earth model results in deceptively large peak displacements at the antipode. Earth’s ellipticity, lateral heterogeneity and a spatially distributed source limit high-frequency waves from constructively interfering at the antipode, thereby reducing peak displacement by a factor of 4. Nevertheless, for plausible impact parameters, we observe peak antipodal displacements of ∼4 m, dynamic stresses in excess of 15 bar, and strains of 2 × 10⁻⁵ . Although these values are significantly lower than prior estimates, mainly based on a point source in a spherically symmetric earth model, wave interference en route to the antipode induces ‘channels’ of peak stress that are five times greater than in surrounding areas. Underneath the antipode, we observed ‘chimneys’ of peak stress, strain and velocity, with peak values exceeding 50 bar, 10⁻⁵ and 0.1 m s⁻¹, respectively. Our results put quantitative constraints on the feasibility of impact-induced antipodal volcanism and seismicity, as well as mantle plume and hotspot formation.