Caption: A cartoon of the formation on the Moon of the Orientale Basin and its antipodal weird terrain.

The hypothesis of formation for structures illustrated in the cartoon (e.g., the Orientale Basin itself and the Caloris Basin on Mercury) is that a massive impactor on a spherical world (in this context meaning planet, moon, etc.) creates a huge impact crater (which could be a multi-ring crater) and that seismic waves from impact event are focussed at the antipodal point of the world by its spherical nature where they cause chaotic or jumbled geology that looks weird, hence is called weird terrain.

Credit/Permission: © David Jeffery, 2004 / Own work.
Image link: Itself.
Local file: local link: moon_orientale_basin_formation.html.
File: Moon: Moonscape file: moon_orientale_basin_formation.html.