Tsunami alerts were issued for Alaska and Hawaii on Tuesday after a major, 8.8 magnitude earthquake struck off the coast of Russia, according to officials.

An 8.8-magnitude earthquake struck off Russia’s eastern coast on late Wednesday morning, local time. The quake triggered tsunami waves across the Pacific that hit Russia, Japan, Canada and parts of the US coast.

Russia’s magnitude 8.8 earthquake spawned serious tsunami warnings, but waves have been moderate so far. Here’s the geological reason why