Thanks to this global monitoring system, which has been deployed for more than 20 years, millions of people in Japan and Russia were warned.

The U.S. Tsunami Warning System ( tsunami.gov) will be updating its guidance as experts learn more about the threat, including maps showing what areas face what risks. In the minutes and hours after a major earthquake, tsunami assessments change as researchers track data from buoy and other interments.

Warnings are now downgraded in most areas. The National Tsunami Warning Centre cancelled its tsunami advisory for coastal B.C. early Wednesday, which stretched from the B.C.-Washington border, north to the B.C.-Alaska border.