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The Honolulu Advertiser
Posted on: Tuesday, January 11, 2005

Hawai'i tsunami zone maps may be flawed

By Deborah Adamson
Advertiser Staff Writer

Hawai'i's tsunami evacuation maps haven't been updated in 13 years and may be inaccurate since they're based on an outdated computer model, several experts said yesterday.

And it will take five to 10 years before the statewide maps will be completely revised to reflect the effect of tsunamis emanating not only from the Pacific Rim but also from elsewhere around the globe and from waters off the Big Island.

"Some of the maps might not be that accurate," said Kwok Fai Cheung, chairman of the Ocean and Resources Engineering Department at the University of Hawai'i-Manoa, who was hired by the state last year to update the maps.

The effects of tsunami generated by local events — earthquakes or undersea landslides — may be significantly under-estimated by the existing maps, he said.

Even though a local tsunami "is not as frequent ... if it happens, the effect would be quite disastrous," he said.

The evacuation maps, found in the front of Hawai'i telephone books, were first published in 1991 and have not been updated since.

While Cheung started working on his project a year ago, the recent Indian Ocean disaster has raised interest in detection and preventive measures in tsunami-prone states, such as Hawai'i.

Cheung has studied the potential of a tsunami impact on O'ahu's North Shore and as a result the evacuation line for parts of the area will be extended farther inland, said Brian Yanagi, tsunami program manager for the state's Civil Defense Division. Cheung's study will cover all coastlines in the state, and could take as long as 10 years to complete, Yanagi said.

The existing maps are one-dimensional, in the sense that they do not take into account the effects of ocean-floor topography that can change the way a wave behaves as it approaches the shoreline. As an example, the shape of the ocean floor in Hilo Bay seems to enhance the power of an incoming tsunami, and that has caused Hilo to be severely impacted by tsunamis in 1946 and 1960, while other parts of the state hit by the same waves did not suffer such severe damage.

The new computer model uses up-to-date ocean-floor mapping data to create what Cheung calls a two-dimensional tsunami map, which he said overcomes the older program's shortcomings.

One of Cheung's main concerns is the effect of a tsunami generated off the Kona coast, which would hit the Big Island in minutes and reach Honolulu in half an hour. He's going to work with the state to possibly develop a second evacuation map that would reflect the effects of a locally generated tsunami.

Gerard Fryer, an associate geophysicist and tsunami specialist at the Hawaii Institute of Geophysics and Planetology, said that with the exception of the Big Island, current evacuation maps should generally suffice for any locally generated tsunamis, even from a 7.8-point earthquake, which he believes is the largest possible there.

However, Fryer acknowledges that the reliability of the current maps has to be confirmed by Cheung's updated methods.

"We don't know they're good until we run the model," he said.

He has already spotted some inaccuracies in the existing tsunami maps: For instance, they show that Ala Moana Boulevard wouldn't be deluged if a tsunami occurs.

"Ala Moana Boulevard is likely to have boats on it," he said.

Staff writer Jan TenBruggencate contributed to this report. Reach Deborah Adamson at dadamson@honoluluadvertiser.com or 525-8088.