The 8.9 magnitude earthquake on Friday, the largest ever recorded in Japan, occurred in a subduction zone, where one of the earth’s tectonic plates is sliding beneath another.

That was the same day as the 9.0-magnitude quake and tsunami hit Japan; however, Japan is on a different tectonic plate.

This structural style displays low-magnitude extension, has overall tectonic geometry of pure shear and forms rift basins.