“It’s a key point to remember that we cannot under-warn. Failure to warn is not an option for us,” Dailin Wang, an oceanographer at centre, told the Associated Press news agency.
Despite the installation of ocean bed sensors and specialised computer mapping, tsunami prediction remains far from an exact science due to the huge volumes of water in the ocean, the impact of the quake on the ocean floor sometimes several kilometres below the surface, and other volatile forces at work.
|Officials say many lessons have been learnt since the 2004 Indian Ocean tsunami [EPA]|
Wang said that while it might appear in retrospect that the threat had been overstated, the lessons learned from the 2004 Indian Ocean tsunami – when more than 250,000 were killed – showed that the proper steps had been taken.
“We cannot have a situation that we thought was no problem and then it’s devastating. That just cannot happen,” Wang said.
In Chile itself the quake did trigger a powerful tidal surge in some areas, killing many of the more than 700 so far confirmed dead in the disaster.
At least five others also died when powerful waves struck Robinson Crusoe Island, about 600km off the Chilean coast.
Chile’s defence minister, Francisco Vidal, admitted on Sunday that the country’s navy had made a mistake in not issuing a general tsunami warning after the quake that could have helped thousands of coastal villagers flee sooner to higher ground.
The waves struck about 30 minutes after the quake itself, raising fears that a powerful surge was making its way across the Pacific, heading for Hawaii, Japan, some of the Indonesian islands and other areas around the Pacific rim.
|Large waves hit Japan, but were well below the massive surge that had been feared [EPA]|
In Japan officials ordered more than half a million people to evacuate seaside areas, fearing that the Chile earthquake could send a tsunami more than three-metres high towards the country’s coast.
The warning of a major tsunami strike was the country’s first in almost two decades.
But in most cases the waves when they finally arrived were less than a metre and caused almost no damage.
The Japanese meteorological agency finally eased the alert at 1015 on Monday morning, after tens of thousands of people spent the night in emergency shelters.
“The agency’s tsunami forecasts turned out to be a bit too big. I’d like to apologise for the prolonged alerts,” Yasuo Sekita, an agency official, told a news conference.
Side of caution
Many of those evacuated felt authorities had been correct to err on the side of caution, given Japan’s experience with earthquakes and tsunamis.
In 1960, a magnitude 9.5 earthquake in Chile, the largest on record, sent tsunami waves up to four metres high slamming into the Japanese coast killing more than 140 people.
|Residents in Hawaii were told to brace for waves over three metres [EPA]|
In Hawaii, the alert from Saturday’s quake triggered coastal sirens, clearing dozens of popular beaches, causing panic buying in some supermarkets and forcing the US Navy to move ships out of the giant Pearl Harbour naval base.
Because of its distance from Chile, the waves took 15 hours to arrive at Hawaii’s shores, and were well below the monster size that had been feared.
However, despite that Gerard Fryer, a geophysicist for the Hawaii-based tsunami warning centre, said the warning had proved a good test case that showed the alarm system worked.
“I hope everyone learned from this for next time, and there will be a next time,” he said.