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

One of the world’s strongest earthquakes struck Russia’s Far East on Wednesday as an 8.8-magnitude tremor set off a tsunami in the northern Pacific and prompted warnings for Alaska, Hawaii and south toward New Zealand.