One of the most powerful earthquakes in modern history shook Russia’s remote east coast Wednesday, sending tsunami waves hurtling across the Pacific Ocean and putting nations from Japan to the United States to Chile on high alert with millions urged to evacuate.

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

Millions of people were evacuated, as minds cast back to the devastating tsunami of Boxing Day 2004 in the Indian Ocean and Japan 2011, both triggered by similarly large earthquakes. But today's tsunami has been much less severe, even though it's brought some damage.