Alaska earthquake prompts tsunami watch in Bay Area

An under sea, 7.9 magnitude Alaskan earthquake set off a tsunami watch along the entire west coast with some people receiving texts and Tweets on their smart phones, but no general alarms or alerts.

At about half past one this morning, the San Francisco Department of Emergency Services texted and tweeted out a tsunami watch; keyword: watch.   It said, "If you are w/in SF & 3 blocks of the Pacific Coast or w/in 5 blocks of SF Bay, PREPARE TO EVACUATE."

"What that means is that the possibility of a tsunami is being evaluated and it is not a confirmed event," said Francis Zamora of the San Francisco Emergency Management Department.

If scientists had confirmed that a tsunami was likely on the way or already occurring, the alert level would have been raised. "Then that would escalate to what's called the tsunami advisory of tsunami warning. From there, we can us things like the sirens, the emergency wireless alerts to get the word out," said Mr. Zamora.

Scientists quickly determined that Tuesday's quake did not generate a tsunami and called off the alerts. Nonetheless, many did not receive any notice at all. That's no surprise to the City's former Emergency Director Lou Canton. "Here in San Francisco we have Alert SF and you can opt into this. But if you're not opted into the system, you won't get the alerts from the system," said Mr. Canton.

Folks on Ocean Beach had different opinions on  how big a tsunami here could be. "I'd say maybe about a hundred feet, maybe a hundred fifty," said a  young woman named Alle. Another man envisioned even bigger waves of Hollywood proportions. "I think just for the action purposes of the movie, just  to emphasize the film," said beach visitor Damian Malone.

So how big a wave could hit San Francisco's Ocean Beach? According to the USGS and other experts, the largest credible wave would be 10 to 15 feet and it would travel about three blocks. A giant wall of water is not likely. 

There are now proposals in Sacramento  to create a single statewide system for all kinds of disasters that could be precisely targeted even down to the square block level. "You want to be able to go to the particular area you want to have evacuated, not necessarily to a large area," said Mr. Canton.

An Alaskan tsunami would take four to six hours to get to the San Francisco Bay Area. A Japanese tsunami would take 12 hours.