For several tense hours Friday, the entire Pacific Coast and Hawaii braced for a possible tsunami.
As word spread of the coming danger, there was widespread fear of a devastating storm surge. Thousands evacuated coastal communities, many spurred by reverse 911 calls like this:
"A tsunami advisory has been issued by the West Coast-Alaska Tsunami Warning Center. The first waves are expected to arrive in Orange County at approximately 8:45 a.m."
Jimmy Kimmel was on vacation in the South Pacific when the tsunami struck Japan. He tweeted: "I am on an island in French Polynesia, glued to CNN." Hours later he tweeted, "we are evacuating the island. dogspeed."
In Santa Cruz, California, boats in one marina were torn from their moorings. Some sank, some floated free, crashing into other boats.
People in low-lying communities like northern California's Crescent City have lived in fear of tsunamis for decades, because a devastating tsunami hit the city in 1964.
Schoolchildren regularly do tsunami drills in class, and even practice evacuating to higher ground.