'Cry wolf' fears for tsunamis
A DETAILED grading system for tsunami warnings, similar to that used for bushfire conditions, is needed to prevent a ‘cry wolf’ perception of the warnings among the Australian public, the head of a local volunteer rescue group said yesterday.
Joint Australian Tsunami Warning Centre co-director Chris Ryan agreed with the call from Ballina Jet Boat Surf Rescue head Garry Meredith, but said the science was not yet advanced enough to provide details beyond the existing two-level system.
Mr Meredith said people in his organisation didn’t notice any effects from Sunday’s tsunami, created by an 8.8 magnitude earthquake off the coast of Chile, and local life guards had a tough time convincing beach-goers to stay out of the water.
“I like the idea of the early-warning system, but it’s a question of how many of those you are going to get before people get blasé about it,” Mr Meredith said.
Mr Ryan agreed the tsunami warning centre had work to do educating Australians about the nature of tsunami warnings.
He also agreed a more detailed warning system would help, but the science had a way to go before that could happen. “Predicting tsunami waves from earthquakes deep under the ocean floor on the other side of the Pacific is a complicated business,” he said.
The warning for the Australian coast for Sunday and yesterday was a Level 1 ‘marine environment’ warning and was never expected to produce visually spectacular waves.
That did not mean there was no risk associated with it, Mr Ryan said. Although the tsunami waves hitting the mainland were smaller than the 50cm waves predicted by the centre’s modelling, the danger was about what was going onunder the water.
Tsunamis created dangerous, rapidly changing and unpredictable currents and rips that could trip up even experienced locals. That meant the marine environment warning was essentially a surf safety warning.
Mr Ryan said the two-level system was designed specifically so the centre could issue a warning ‘without giving the impression there would be a gigantic wave’.
“Obviously we’ve not been completely successful in removing that perception,” he conceded.
The other warning, Level 2, land environment, was the one that was likely to yield spectacular waves and would trigger the evacuation of coastal communities.
The centre had not yet issued one of those – and it would likely be a long time before it gets the chance to do so.
While Australia’s east coast was exposed to several potential sources of tsunamis – including the Chilean fault line that delivered Sunday’s and yesterday’s waves – it was also relatively protected by the broad, flat Tasman Sea and continental shelf, which diffused the power of tsunamis and reduced their impact when they hit the coast.
However, that did not mean Australia was not at risk.
Mr Ryan said a magnitude 8.5 or higher quake at certain points of a network of undersea volcanoes running from New Zealand toPapua New Guinea could trigger tsunamis able to cause serious damage in coastal communities.