[MainFrame65]

The math is well beyond me, but I believe that the idea is that the stricture of the Earth would act as a lens and mirror system, with the varying densities of the inner core, mantle, and crust, as well as the boundary effect of the outer spherical surface acting to focus the energy on the opposite side (antipode).

I don't know if it relates, but if you drop a heavy ball straight down into a pool, the water flows around the top of the ball and spouts upward rather than just splashing out.

[gcruse]

Lensing is certainly possible. But think how much power it would take to punch a hole in the mantle...