FRANKLYWNOW - What goes into a tsunami warning?

At the National Tsunami Warning Center in Palmer, director Paul Whitmore has an extremely important job after an earthquake: Warning communities that might be affected by a tsunami.

“It can be as short as minutes,” Whitmore said. “In 1964 some communities had impacts from a tsunami before the earthquake even stopped shaking.”

He said the circumstances of the ’64 quake are rare. A tsunami would reach most cities within 15 to 20 minutes of a major earthquake.

Three factors go into deciding to issue a warning: Location, depth and magnitude.

“Location — whether it’s on shore or off shore. The depth of the earthquake — whether it’s shallow up on the crust or deeper, and magnitude… the magnitude is the biggest criteria,” Whitmore explained.

The center won’t issue a warning unless the magnitude is 7.1 or higher, which is the magnitude seismologists gave Sunday’s quake. The deep epicenter — more than 75 miles down — didn’t make it a threat though.

Whitmore said people in the Anchorage area unlikely to ever see a tsunami because of the shallow water in Cook Inlet. The Alaska Earthquake Center at the University of Alaska Fairbanks put out a model demonstrating how the waves would impact Alaska’s largest city.

“You can see a lot of energy as it moves up Cook Inlet, it’s dissipated, and by the time we get to Anchorage there’s very little impact at all,” Whitmore pointed out.

While Anchorage may be safe, Whitmore said other coastal communities always need to be aware of the danger.

“If they feel a strong earthquake that lasts for 20 to 30 seconds or more, that’s nature’s indicator a tsunami may be imminent,” he said.

After Sunday’s shaker, the community of Nanwalek had several people evacuate to higher ground, despite the lack of a tsunami warning. Whitmore said it’s always better to be safe than sorry.

If a tsunami warning is issued, the first place it will be posted is on the National Tsunami Warning Center’s website.

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