The odds are nearly 1-in-10 that a giant tsunami will hit Hawaii in the next 50 years from an earthquake in the Aleutian Islands, University of Hawaii researchers reported Friday.
The tsunami, equivalent to the one that ravaged Japan in March 2011, would inflict $40 billion in damage here, the researchers estimate, citing a 2013 state report.
The scientists, led by UH-Manoa geophysicist Rhett Butler, created a model based on the five largest quakes to rock the earth since 1900. They include the 2011 Tohoku quake in Japan, the Sumatran quake of 2004, the 1964 Alaska quake, the 1960 Chile quake and one in Kamchatka, Russia, in 1952.
All were magnitude 9.0 or greater.
“These five events represent half of the seismic energy that has been released globally since 1900,” Butler said in a statement Friday. “The events differed in details, but all of them generated great tsunamis that caused enormous destruction.”
In a telephone interview Friday, Butler compared the process to determining the value of a house.
“What’s your house worth? Well, you don’t know. But what an appraiser does is look at comparables. That’s what we did. We looked at comparables for tsunamis from other magnitude-9s.”
The model also takes into account the rate of subduction — the Pacific plate grinding under the North American plate — and the length of the Aleutian subduction zone, he said.
They came up with a probability of 9 percent plus or minus 3 percent for a magnitude-9.0 in the Aleutians over the next 50 years. The chances are less — 3.5 percent — for a quake of that size in the section of the Aleutians directly facing Hawaii.
“That is what I consider the worst case, with the energy focused directly at Hawaii,” Butler added. But a large quake doesn’t have to be in that zone to cause destruction in Hawaii.
Butler and co-authors Neil Frazer, a UH geology professor, and William Templeton, now at Portland State University, published their findings in Solid Earth, a journal affiliated with the American Geophysical Union.
To refine the probability estimates, they took into account prehistoric tsunamis, including one that hit Kauai in the 16th century, placing ocean deposits in the Makauwahi sinkhole, 300 feet from the ocean near Kalaheo.
“We were surprised and pleased to see how well the model actually fit the paleo-tsunami data,” Butler said.
The $40 billion damage estimate comes from the 2013 Multi-Hazard Mitigation Plan, prepared for state Civil Defense.
The UH team is now considering ways to extend the analysis to smaller earthquakes, magnitude
7 or 8, around the Pacific.