By Evan Bush, NBC News

The magnitude-8.8 earthquake off Russia’s Kamchatka peninsula sent a wave of water racing at the speed of a jetliner toward Hawaii, California and Washington state, spurring warnings and alarm overnight Wednesday.

But when the tsunami waves arrived, they didn’t cause devastation or deaths in the United States, and the inundation might not have appeared threatening in some locations where warnings were issued.

That doesn’t mean the tsunami was a “bust,” that it was poorly forecast or that it didn’t pose a risk, earthquake and tsunami researchers said.

“You start to hear ‘tsunami warning,’ and everyone immediately thinks of the last Hollywood movie they saw, and then it comes in at 3 feet and people are like, ‘What’s that?’” said Harold Tobin, the director of the Pacific Northwest Seismic Network and a professor at the University of Washington. “We should count it as a win that a tsunami occurred, we got a warning and it wasn’t the worst-case scenario.”

Here’s what to know.

How strong was the Kamchatka earthquake? And why did it change so much?

Initial reports from the U.S. Geological Survey pegged the Kamchatka earthquake at magnitude 8.0. Later, it was upgraded to 8.8.

“That is not uncommon for very, very large earthquakes in those initial minutes,” Tobin said. “Our standard algorithms for determining the size of an earthquake quickly saturate. It’s like turning up an amp and getting a lot of distortion.”

One of the first signs the earthquake was stronger than the initial seismic reports said was an initial measurement from a buoy about 275 miles southeast of the Kamchatka peninsula.

The buoy, which is part of the National Oceanographic and Atmospheric Administration’s DART (Deep-ocean Assessment and Reporting of Tsunamis) system, is connected to a seafloor pressure sensor about 4 miles below the surface.

The sensor registered a 90-centimeter wave — more than 35 inches — which is eye-popping to tsunami researchers.

“That’s the second-largest recording we ever saw in the tsunami world,” said Vasily Titov, a senior tsunami modeler at NOAA’s Pacific Marine Environmental Laboratory, adding that it indicated there was “a catastrophic tsunami propagating in the ocean.”

Titov said the only higher reading was from the 2011 Tōhoku earthquake and tsunami, which killed nearly 16,000 people in Japan.

Seismic models later confirmed that Wednesday’s earthquake was magnitude 8.8, which means it released nearly 16 times as much energy as a magnitude-8.0 earthquake, according to a USGS calculation tool.

Tōhoku was much bigger.

Tobin estimated that earthquake released two to three times as much energy as was observed in Kamchatka. Titov said the tsunami in Japan was also about three times larger.

In addition, he said the Tōhoku earthquake “produced an anomalously large seafloor displacement,” lurching and moving more water than expected, even for an earthquake of its magnitude.

At Kamchatka, “it’s likely that there was less seafloor displacement than could have happened in a worst-case or more dire scenario for a magnitude-8.8,” Tobin said, though more research will be needed to confirm that theory.

[…]

Why were people in Hawaii evacuated for a 5-foot wave?

Yong Wei, a tsunami modeler and senior research scientist at the University of Washington and the NOAA Center for Tsunami Research, said a 1.5-meter (5-foot) tsunami wave can be very dangerous, particularly in shallow waters off Hawaii.

Tsunami waves contain far more energy than wind waves, which are far shorter in wavelength and period (time between waves) and slower in speed.

Wei said tsunami waves of the size that struck Hawaii can surge inland “tens of meters,” produce dangerous currents and damage boats and other moveable objects.

“People die. If they stay there and they don’t get any warning, 2 meters can definitely kill people,” Wei said. “If you’re on the beach, strong currents can definitely pull you out into the ocean and people will get drowned.”

Tobin said the initial warnings were conservative but appropriate, in his view.

“I don’t want people to think, oh, we had a warning and nothing much happened and pooh-pooh it — ‘I can ignore it,’” he said. “Warnings by nature have to err a bit on the side of caution.”

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Read more about CICOES research on tsunami forecasts and modeling.