California’s tsunami watch was a false alarm, but what if one actually hit SLO County?

Avila Beach is one of many areas of San Luis Obispo County that would be vulnerable to a tsunami.
Avila Beach is one of many areas of San Luis Obispo County that would be vulnerable to a tsunami.

It was half past midnight on Tuesday when an earthquake — magnitude 7.9 — struck in the Gulf of Alaska, jolting many Alaskans from their beds and sending them scrambling for higher ground as tsunami alerts were sent out across the state and down the West Coast.

The “Good Friday Earthquake” that hit Alaska in 1964 — which at magnitude 9.2 is the most powerful quake recorded in North American history — and the tsunami devastation it wrought were still a living memory for many. A tsunami from that earthquake also killed 12 people in Crescent City and did significant damage to Morro Bay’s harbor.

More recently, an earthquake in northern Japan in March 2011 generated a 6- to 9-foot surge on the Central Coast that did $500,000 worth of damage to Morro Bay docks and piers.

Read Next

An earthquake with a preliminary magnitude of 8.2 struck off Alaska’s Kodiak Island early Tuesday, initially prompting a tsunami warning. The warning has since been cancelled, but an advisory remains for part of the state.

The National Weather Service’s tsunami watch for the California coast Tuesday morning was canceled, but the question remained: What if there were a tsunami here?

While tsunamis primarily pose a risk along San Luis Obispo County’s coastal communities, those wouldn’t be the only places potentially affected, SLO County Emergency Services Manager Ron Alsop said.

A tsunami along Avila Beach could cause San Luis Creek to overflow, causing flooding as far inland as Highway 101, he said. In Cambria, Santa Rosa Creek poses the same concern.

As for warning time, Alsop said it all depends on where the earthquake strikes. One in Japan or Alaska will allow officials more time to formulate a response, while a local earthquake, or one just offshore, would afford virtually no time at all.

“It’s extremely unlikely to have a local earthquake that has a significant tsunami impact,” Alsop said.

If given enough notice, Alsop said “we have a number of ways” to reach the public. One of the key ways, he said, was through the National Oceanic and Atmospheric Administration, which broadcasts weather information as a public service. A special receiver is needed to pick up its VHF signal, however.

Members of the public also can sign up for reverse 911 phone calls from the San Luis Obispo County Sheriff’s Office.

The county also has the ability to send out alerts via radio and TV broadcasts and on cellphones, he said. In the event of a late-night or early-morning alert, such as the tsunami watch issued Tuesday, Alsop said the county has early warning system sirens, and officials could also drive through neighborhoods speaking on a public-address system.

Because of the presence of Diablo Canyon nuclear power plant, “we’re actually required to demonstrate to (Federal Emergency Management Agency) that we can do this route alerting,” Alsop said.

The county also is in the permitting process to install tsunami zone signs along the coastal highways.

Andrew Sheeler: 805-781-7934, @andrewsheeler

Do you know what to do if you accidentally dial 911? Do you know what information is crucial in an emergency? Here's what you need to know to get the police, fire or ambulance service you need fast.

Tsunami warning signs

Tsunamis are triggered by earthquakes. Warning signs that a tsunami may be imminent include sudden shaking, a loud roaring sound coming from the ocean or sudden dramatic rise or fall of the tide. If you see any of those warning signs, you should move inland and uphill as fast as you can.

Tsunami waves appear like a sudden surge or flood and can consist of several waves.

More information: www.slocounty.ca.gov/Departments/Office-of-Emergency-Services.aspx.