Posted on: Thursday, December 30, 2004
Scientists wary of another tsunami
| • | Chart (opens in a new window): Pacific and Indian Ocean earthquakes |
By Jan TenBruggencate
Advertiser Science Writer
Geologists are closely monitoring aftershocks from Sunday's immense earthquake off the Indonesian island of Sumatra and worry they could cause more property damage and perhaps launch another tsunami.
Rescue personnel and survivors of the Indian Ocean tsunami are being shaken regularly by the aftershocks, which could last for another year.
"In earthquake forecasting, we generally cannot be very specific about when the next big earthquake is going to be, but you can forecast that large quakes will continue to happen up to a year or more," said Brian Yanagi, tsunami program manager with Hawai'i Civil Defense.
Yanagi said one benefit of the disaster to Hawai'i is that people and institutions are paying a great deal of attention to the potential threat of tsunami in Hawai'i.
"We're planning a tsunami exercise April 1 (the anniversary of a catastrophic tsunami that hit Hawai'i in 1946). Response to participation has skyrocketed. Until now, it has been hard to keep people interested in these exercises," Yanagi said.
The exercise mainly will involve government agencies and emergency relief services.
The need for vigilance in Hawai'i persists even while the world's focus is on the Indian Ocean, geologists say.
Tsunamis that have caused damage in the Islands during the past 60 years have come from the Aleutians (1946), Kamchatka (1952), Chile (1960) and Alaska (1964), and from an earthquake near Kalapana on the Big Island (1975). A 1994 earthquake in Japan's Kuril Islands prompted a statewide coastal evacuation in Hawai'i, but the wave measured only a few inches locally.
All of those Pacific Rim areas continue to shake. Just in the past week earthquakes in excess of magnitude 5 originated in the Aleutians and Japan.
"Those areas are always bubbling," Yanagi said.
Tsunami usually are generated by a violent undersea disturbance or activity near the coast or in the ocean. By far, the most destructive tsunami are generated from large, shallow earthquakes with an epicenter or fault line near or on the ocean floor. Usually, it takes an earthquake with a magnitude exceeding 7.5 to produce a destructive tsunami, according to the International Tsunami Information Center.
"It would be highly unlikely to have another (magnitude) 9 earthquake. That was a huge quake and it probably relieved the major stress in that region," said Charles "Chip" McCreery, geophysicist in charge at the Pacific Tsunami Warning Center in 'Ewa Beach.
There was a quake of magnitude 7.1 less than four hours after the big Sumatra quake. The activity seemed to taper off, then picked up again yesterday.
"We went 48 hours without a 6, then this morning we had two 6s, a 6.1 and a 6.2," said Waverly Person of the U.S. Geological Survey Information Service in Golden, Colo., yesterday.
"We have had reports that they were feeling these aftershocks, and some of the people are jumpy because now they know what it can mean," Person said.
Residents of many regions near the Sumatran site of the big earthquake were able to feel the earth move well in advance of the arrival of the tsunami. If they had recognized the danger, there likely would have been enough time to flee to safer ground.
"Many of the people close to the earthquake felt the shaking, but they didn't know what to do. The people in the area had not been educated in what to do," Person said.
Reach Jan TenBruggencate at jant@honoluluadvertiser.com or (808) 245-3074.
