Civil defense officials stress
need for tsunami awareness

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By Helen Altonn
haltonn@starbulletin.com

A tsunami generated by an earthquake in the Aleutian Islands on April 1, 1946, killed 96 people in Hilo, 15 on Kauai, 14 on Maui and nine on Oahu -- a total of 159.

The first statewide tsunami exercise this year is scheduled for tomorrow to mark the worst natural disaster in Hawaii's history and the start of Tsunami Awareness Month.

The Hawaii Warning System's monthly siren test at 11:45 a.m. tomorrow will trigger a wave of behind-the-scenes activity to test the system's response to a locally generated tsunami.

State and county civil defense and tsunami warning officials emphasized at a workshop last Tuesday at the National Weather Service that a tsunami could occur at any time.

They are most concerned about what Ralph J. "Jeff" LaDouce, Pacific Region director of the weather service, calls "hazard amnesia" resulting from the infrequent occurrence of tsunamis.

He said the public must be reminded that hurricanes and tsunamis are real hazards, especially locally generated tsunamis that allow little or no time for official warnings.

"There is a 100 percent guarantee that we will have an attack on Hawaii from a destructive tsunami over time," said Brian Yanagi, state Civil Defense earthquake/tsunami program manager. "History has shown this."

Earthquakes off the Big Island caused tsunamis in 1868 and 1975. The 1868 Kau earthquake killed 47 people and caused a landslide in Pahala that killed another 37. Its magnitude was estimated at 7.8 on the Richter scale.

The last deadly tsunami in Hawaii, which killed two people and injured 19 in 1975, was triggered by a Kalapana earthquake estimated initially at 7.2 on the Richter scale.

It has since been upgraded to 7.6 by Harvard's seismology laboratory, said Gerard Fryer, University of Hawaii geophysicist and co-state tsunami adviser with seismologist Laura Kong.

Tomorrow's exercise will focus on the worst likely scenario, a tsunami caused by an earthquake in south Kona. The scenario is based on modeling studies by Fryer and Philip Watts of Applied Fluids Engineering Inc. to calculate damage from locally generated tsunamis on the Big Island.

"The island is a heavy burden on the crust of the Earth," Fryer pointed out, explaining it is sitting in a hollow with magma filling the rift zones. The pressure causes the mountain to slide sideways over the old sea floor, causing a basal-slip earthquake, he said.

In the 1975 earthquake, a big piece of Kilauea moved and pushed the ocean up, resulting in a tsunami, he said.

A big earthquake at Kona would be "a Kalapana-like event -- twice as big," with a tsunami reaching Maui and Oahu in about 30 minutes, he said.

Yanagi said a 6.2 magnitude earthquake has about the same energy as the atomic bomb dropped on Hiroshima and a 7.2 earthquake is 32 times more powerful.

Fryer said the evacuation zones for Honolulu, shown in maps in the telephone book, "by and large are real good." Two areas that might be in trouble are Iwilei, in the back of Honolulu Harbor, which would overflow, and Kewalo Basin, he said.

Residents should listen to TV or radio for warning information when sirens are sounded, look at evacuation maps and leave immediately if they're in an evacuation area, said John Cummings, Oahu Civil Defense Agency education and training officer. "Go vertical" in Waikiki, he said.

In 1975, she said, the ground sank 12 feet at Kalapana, and a tsunami arrived with wave heights on land of 47 feet.

A tsunami consists of a series of waves, and the first ones aren't necessarily the largest, added Dan Walker, retired UH geophysicist, now tsunami adviser to the Oahu Civil Defense Agency.

Charles McCreery, geophysicist in charge of the Pacific Tsunami Warning Center at Ewa Beach, said with automated processes, the center has reduced warning time for local earthquakes to under five minutes from 10 or 20 minutes.

He said the initial warning is based on seismic data because of a good possibility a damaging tsunami was generated. Scientists then look immediately at sea level data, "because waves can be on shore in minutes."

The center collects data from seismic stations across the state, as well as 50 stations operated by the Hawaii Volcano Observatory on the Big Island and a network of sea level gauges.

Walker also has developed sensors that would immediately trigger an alarm at the warning center if flooded by a tsunami. Eight have been positioned along the Kona coast about 10 feet above sea level. They aren't affected by storm surf, and they've worked fine in every test, he said. He'd like to put some along the Puna Coast, but there are no poles for them, he said.