VANCOUVER -- Some residents along British Columbia's coastline were woken by tsunami warning sirens early Tuesday morning shortly after an earthquake struck off the coast of Alaska. Here are some things to know about tsunami alerts in Canada:
-- British Columbia learns about potential tsunamis from the U.S. National Tsunami Warning Center.
-- The centre uses seismometers and sea level measuring stations, which send real time data to national and regional warning centres, to determine whether there's a risk.
-- After receiving notice from the U.S., federal and provincial emergency officials assess the information to determine whether it poses a threat to B.C.
-- There are five levels of alerts that B.C. can send out: a warning, an advisory, a watch, an information statement and a cancellation.
-- A tsunami warning means that a "flood wave" is possible and a full evacuation is suggested.
-- An advisory means there will likely be strong currents and people should stay away from the shore.
-- A watch means the government does not yet know how dangerous the situation is, and people should stay alert as they wait for more information.
-- An information statement warns an earthquake has occurred, or that a tsunami warning, watch or advisory has been issued for another section of the ocean. But in most cases, there is no threat of a destructive tsunami.
-- A cancellation is issued when there's no longer a threat.
