Quakes can be followed by deadly waves

In coastal areas, strong quake should motivate people to higher ground

Posted: Saturday, March 04, 2000

Earthquakes may be one of the most feared and destructive forces in Alaska.

But it is their close cousin, the tsunami, which has a fatal reputation.

In the aftermath of the 1964 Good Friday earthquake, the majority of deaths were from the resulting tsunamis -- seismic sea waves -- which reached as far south as northern California, where two people were killed. In all, 131 people were killed by the quake and tsunamis.

According to Paul Whitmore, a geophysicist at the Alaska Tsunami Warning Center, the key to avoiding danger is being aware of the risk.

"Any place, really, along the ocean can be in danger," Whitmore said. "Historically the open ocean side of the Kenai Peninsula has been more at risk."

Any strong earthquake can cause a tsunami, as can large landslides, which may follow. Because events happen so quickly, it is important to head for higher ground as soon as possible.

"If you feel a strong earthquake that shakes for 20 to 30 seconds, that makes if difficult to stand, don't wait for official warning," said Whitmore.

The ideal elevation, he said, is at least 100 feet above sea level, since tsunamis of that size are extremely rare.

A common misconception is tsunamis are large walls of water, which crush everything in their path, then quickly recede.

Whitmore said reality doesn't match that Holly-wood image.

"If you have a 5-foot tsunami, that means there's going to be a 5-foot rise in sea level," he said. "It's like a tide cycle that's compressed and magnified."

What separates tsunamis from floods are currents that can reach 20 to 30 knots and will happen several times, anywhere from every 5 minutes to every half hour.

Whitmore said the most common cause of injuries is returning to sea level before it's safe.

"Sometimes people tend to return to shore too early," said the geophysicist. "Usually it's the most dangerous in the first couple of hours."

He recommends waiting until two hours after strong waves have stopped, or if at night, until daybreak. It is also possible to measure safety with tidal gauges.

"If you feel the earthquake, don't wait for official warning," Whitmore reiterated. "Once you're in, it's kind of late."

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