Anisotropy:
[Thanh-Son] Pham said the speed likely differs [in the core] based on the wave direction due to a physical property known as anisotropy, which allows a material to possess different properties in different directions. We commonly see anisotropy in wood, which is easier to chop along its grain than against it. [“Scientists have discovered a new core at the center of the Earth,” Kasha Patel, WaPo]
