Indian Ocean tsunami alerts improve

By Adhityani Arga

JAKARTA (Reuters) - Tsunami warning systems in the Indian Ocean have improved since the devastating 2004 Indonesian quake but still have many flaws and produce false alerts or miss potential threats, experts and officials said on Friday.

Authorities in nations ringing the Indian Ocean issued a series of tsunami alerts this week after a powerful quake hit Indonesia's Sumatra Island on Wednesday, followed by more than 40 aftershocks of between magnitude 4.9 to 7.8.

So far, there only appear to have been a few localised and non-fatal tsunamis in Sumatra, but experts said the region was lucky to have escaped a tsunami similar to the one off Indonesia's Aceh which killed more than 280,000 people in 2004.

Seismologist Mike Turnbull of Australia's Central Queensland University said authorities had not over-reacted this week.

"It would have been irresponsible not to issue the warnings because all the scientific evidence (was) available at the time when the warnings were issued," Turnbull said by telephone.

In Indonesia, any undersea quake measuring more than 6.3 on the Richter scale and less than 70 km deep automatically triggers a tsunami warning in earthquake centres and then a seismologist reviews the data before deciding whether to issue an alert.

Pariatmono, an official at Indonesia's research and technology ministry, said a warning, even if it was false, was better than none, but admitted to flaws.

"At the moment the system is not fully reliable, and that is why there are many false warnings," he said by telephone.