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Thursday, November 20, 2014         

KOKUA LINE


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Tsunami wave height not basis for setting inundation zones

By June Watanabe

POSTED:



Question: With regard to the maps of tsunami evacuation zones, do you know at what wave or surge height these are based on? The tsunami in Japan was reported at 23 feet in some areas. It was also reported that the surge traveled three miles inland. The maps don't indicate what height is anticipated, so I can’t tell whether these are best- or worst-case scenarios.

Answer: The maps are not based on waves of a specific height.

Rather, they’re based on “significant tsunamigenic earthquakes that might occur around the Pacific Rim,” said Kwok Fai Cheung, professor in the Department of Ocean and Resources Engineering at the University of Hawaii at Manoa.

Hawaii State Civil Defense updated its evacuation zones last year, based on tsunami inundation maps that Cheung developed. Inundation refers to how far inland tsunami waves might travel.

Cheung studied five destructive tsunamis that struck Hawaii during the past century, generated by the 1946 Aleutian earthquake, the 1952 Kamchatka earthquake, the 1957 Aleutian earthquake, the 1960 Chile earthquake and the 1964 Alaska earthquake.

Those tsunamis were modeled on the computer and studied to develop the worse-case inundation scenarios, Cheung said.

Additionally, he considered hypothetical tsunamis generated by magnitude-9.5 earthquakes from Japan, the Marianas, the Solomon Islands, Tonga and the Pacific Northwest.

Cheung explained that evacuation maps might extend further than inundation maps because, for example, “the water might stop in the middle of a city block, but for evacuation purposes, you don’t want to confuse people, so you evacuate the entire block.”

The evacuation maps rely on roadways or other identifiable features as landmarks.

Cheung also said that sometimes the evacuation zones might depend on what law enforcement resources are available to help get people to safety.

It’s not “rational” to use a single wave height to determine inundation zones, he said, because the wave energy might be focused in one location but be distributed over a larger area in another location.

“I modeled the tsunamis all the way from the source, accounting for all the transformation across the Pacific Basin” as well as local conditions, Cheung said. “We take all those (factors) into account to determine the inundation (maps).”

The evacuation zone maps can be found on the city Department of Emergency Management website, www1.honolulu.gov/dem/draft_tsunami_evacuation_zone_maps_.htm, the State Civil Defense website, www.scd.hawaii.gov or in the telephone directory.

AUWE

To all the people who returned grocery carts of food and water the day after the March 11 tsunami. You folks hoarded all these items, making it almost impossible for others to purchase them. Maybe you should purchase things you actually are going to use whether we have a tsunami or not!
Concerned Citizen

Write to “Kokua Line” at Honolulu Star-Advertiser, 7 Waterfront Plaza, Suite 210, 500 Ala Moana Blvd., Honolulu 96813; call 529-4773; fax 529-4750; or e-mail kokualine@staradvertiser.com.






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