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Researcher: Hilo evacuation maps should account for possible megatsunami

Hilo’s existing tsunami evacuation zones are not sufficient to respond to a hypothetical megatsunami, according to a University of Hawaii researcher.

Back in 2011, the Hawaii Emergency Management Agency and the Pacific Tsunami Warning Center began work on new tsunami models for the state after the Tohoku earthquake and tsunami struck Japan.

Those models were completed in 2015 and were subsequently incorporated into updated tsunami evacuation plans on Oahu, Kauai and Maui — but not on Hawaii Island.

However, Hawaii County Civil Defense Director Talmadge Magno said such an update would be superfluous.

“When our evacuation maps were drawn up, (former Civil Defense Director and Mayor Harry) Kim added this buffer zone around the evacuation zone,” Magno said.

That increased space added to the evacuation zone encompasses a model of the worst-possible scenario developed by the state in 2015, Magno said.

“That’s not an accurate statement,” said Kwok Fai Cheung, a professor of ocean resources and geoengineering at UH-Manoa who developed the updated models.

Cheung’s models, he said, are mostly covered by Hawaii County’s evacuation plans, but there are certain areas where the worst-case model exceeds the evacuation plan.

“Hilo is one of those places,” Cheung said, explaining that the worst-case model extends south of Hilo International Airport, while the current plan only extends to the north edge of the airport. Other sites in Kailua-Kona and Kawaihae are similarly not covered by the evacuation plan.

“I’ve offered to help (Hawaii) County multiple times, even though my contract with the state has run out,” Cheung said, although he added that Hawaii County Civil Defense had different leadership when he presented his models to them, and therefore might not be aware of the most updated models.

Before the Tohoku quake, the state’s tsunami evacuation plans were based on the impacts of tsunamis that struck within the last 100 years, Cheung said.

However, the Tohoku tsunami was more powerful than any other to have struck the region in the last century, and overwhelmed the Japanese tsunami defense measures, leading to more than 14,000 deaths in the immediate aftermath of the disaster.

In the wake of the Tohoku quake, Cheung said the state realized that its models should consider not only the tsunamis of the recent past, but also a hypothetical worst-case scenario in order to avoid future disaster. To that end, Cheung’s models imagined a 9.6-magnitude earthquake originating from the Aleutian Islands.

UH-Manoa geophysicist Rhett Butler, former director of the Hawaii Institute for Geophysics and Planetology, said an Aleutian quake is the most plausible source for a Hawaii megatsunami.

“The Aleutians are right there, and they’re pointed straight at us,” Butler said, but added that potential tsunami-triggering quakes also could originate from around the Kamchatka Peninsula in Siberia. A Kamchatka tsunami, however, would take much longer to reach Hawaii.

Butler said there is compelling, although not conclusive, evidence that a similar megatsunami event struck the islands about 300 to 350 years ago, based on sediment deposits on Kauai. Such events are estimated to occur once in a millennium.

The 1946 tsunami that hit Hilo, which occurred 75 years ago Thursday, originated from an 8.6-magnitude Aleutian quake.

Magno said Civil Defense reviews the county’s tsunami evacuation plans every year, and will run a training exercise at the Hilo International Airport later this year.

Email Michael Brestovansky at mbrestovansky@hawaiitribune-herald.com.
Source: Hawaii Tribune Herald

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