Japan-Level Tsunami Damage Unlikely in Hawaii
The images of massive tsunami waves crashing through the countryside, tossing cars like toys and erasing entire towns broadcast to the world from Japan last week are unlikely to be replicated in Hawaii even under the worst set of circumstances, experts say.
A federally-funded University of Hawaii study to model the “credible worst case scenario” for a tsunami hitting the Hawaiian Islands has already been used to update Oahu’s evacuation maps, while the Big Island claims its maps were already sufficiently conservative to require no changes.
Kwok Fai Cheung, a professor in the University of Hawaii‘s Department of Ocean and Resources Engineering, designed the worst-case inundation models based on the largest Hawaii tsunamis during the last century and hypothetical events originating at earthquake hotspots near and far.
“The maps are based on the five historical events and then we did additional analysis to confirm the maps are OK for a significant event from elsewhere in the Pacific Basin,” he told Civil Beat Monday.
The five historical events considered were 1952 in Kamchatka, 1946 in the Aleutian Islands, 1957 and 1964 in Alaska and 1960 in Chile, Cheung said.
The hypotheticals doubled the size of the quake that started the deadly tsunami in Sumatra and the Indian Ocean in 2004 and transplanted that event to spots on the Kuril Islands north of Japan, the Mariana Islands, the Solomon Islands, Cascadia, Tonga and Japan, he said.
For good measure, he also included three hypothetical magnitude 7.5 tsunami events on the west side of the Big Island that would send energy back toward the rest of the state. All scenarios were run at high tide, “just to be conservative.”
The project calls for Cheung to provide his inundation maps to the county civil defense agencies, which then tweak them to maximize the efficiency of police roadblocks and other evacuation-related government operations. His Oahu model, published in 2008, inspired the City and County of Honolulu to move the border of the evacuation zone a few blocks mauka in at least one location.
“For East Honolulu, if you look at the evacuation maps from an old telephone book, you would see the evacuation zone stop at Kalanianaole Highway,” Cheung said. “Now the new evacuation map shows part of the valley, people living in the valley adjacent to the highway would have to be evacuated.”
His Big Island work was completed in 2010, too late to be incorporated in new maps in time for the event last week, and Cheung declined to provide details. Hawaii County Civil Defense Administrator Quince Mento said the county reviewed the models and determined it didn’t need to make any changes.
“Our evacuation lines are so conservative to begin with that there wasn’t any need to alter any of it,” he said.
The evacuation maps are designed to facilitate an orderly process that could take up to three hours to complete. In the event of a tsunami generated near Hawaii’s shores — like the 1975 quake Cheung based some of his hypotheticals on — there would be little time for warnings. A wave could reach shore in a matter of minutes, and could even travel from the Big Island to Honolulu in less than half an hour.
Geophysicist Gerard Fryer of the Pacific Tsunami Warning Center, part of the National Oceanic and Atmospheric Administration’s National Weather Service that monitored last week’s event, said he hopes his team can get a warning out in less than two minutes, and that counties would quickly sound the sirens when given the heads up.
“They’ve been told, ‘Don’t ask questions. If we say sound your siren, you just press the button.'”
A local earthquake is unlikely to be anywhere close to the magnitude 9.0 temblor that shook Japan Friday. Hawaii is comfortably inside the ring of fire that generates the vast majority of the world’s seismic activity.
“The source is so much smaller than the Japanese earthquake, so it’s going to die down with distance that much more quickly,” Fryer said. On top of that, Hawaii’s coast is better-equipped to resist even large waves.
“The Big Island has a steeper slope than the coast of Japan so the tsunami can’t get as far on shore before it runs out of steam,” Fryer said.
Still, Cheung has advice for Big Island residents if they feel a serious ground-shaking, building-swaying quake: Run.
“If you’re on the Big Island, and you feel the earth quake, just run, don’t wait for the siren.”
