Page last updated at 09:42 GMT, Thursday, 6 May 2010 10:42 UK

Tsunami alerts 'confuse public', says Noaa scientist

By Jonathan Amos
Science correspondent, BBC News

Boat lifted on to land by tsunami (Getty Images)
Locally in Chile, the tsunami arrived within half an hour

Tsunami warnings need to convey information that is more meaningful to the public, a top US researcher says.

Traditional alerts that have focussed on "wave amplitudes" are confusing to most people, says Dr Vasily Titov.

The scientist, who directs Noaa's Center for Tsunami Research, thinks more practical information such as the risk of flooding is also needed.

He says this is one of the key lessons from the recent Magnitude 8.8 Chilean earthquake and subsequent tsunami.

"We're scientists and we're really proud of our models and our accuracy but we realised after the Chilean tsunami that when we convey this information to the public there is a gap between what we are saying and what is understood," he told BBC News.

"When we say there is a two-metre wave amplitude expected, the general person imagines a two-metre wall of water.

"But that's not what amplitude means - tsunami would very rarely come as a wall of water. It refers to the amplitudes at tide gauges and it is peak to trough. It will not be the wave height that a surfer or someone on the beach sees."

Dr Titov was speaking here at the European Geosciences Union meeting.

Big test

The 27 February quake which had its epicentre some 11 km off the coast of the Maule region of Chile marked a major milestone for tsunami forecasting.

It was the first basin-wide event generated in the Pacific since the Great Alaskan Earthquake of March 1964, and the first occurrence since Sumatra in 2004 that enabled modellers and forecasters to test their capabilities over such a wide area.

At Chile itself, the proximity of the quake to the coastline meant the tsunami arrived within 30 minutes, with water running up some 10 to 15 metres above the expected sea level in places. But even as far away as Hawaii, there was inundation of water with amplitudes of about 2.5m.

The warnings put out by the Noaa Pacific Tsunami Warning Center proved to be highly accurate when the predictions of wave behaviour were checked against what actually happened at tide gauges.

Forecast travel times for the tsunami across the Pacific basin demonstrated an average accuracy of 98%. The forecast of maximum wave amplitudes had an accuracy above 80%.

Forecast amplitudes for the Chilean earthquake tsunami (Noaa)
The modelling and forecasting have become extremely detailed and skilful

This level of success means Noaa could be very confident about its flooding forecasts, which should now be more prominent in the public release of information, said Dr Titov.

"You want to send a message that will be immediately understood and immediately acted upon.

"We can now convey very simple information such as the likelihood that flooding will occur for a tsunami. The warning products coming out of tsunami warning centres should probably reflect that. Instead of saying amplitudes of two or one metre are expected in a location, the message should say whether flooding is expected in this location and whether people need to evacuate or not.

"You probably want to have some information about the currents that will be induced in some harbours and ports. That's very important for the marine industry. It really has to be specific to the target audience."

Tsnumai flood maps (Noaa)
The public need information they can act on, says Dr Titov

In Chile, some lessons also need to be learned, seismologists told the EGU meeting.

The country's location at the convergence of the Nazca and South American tectonic plates means it is certain to be hit by more major quakes in future, some of which could also generate substantial tsunamis.

This February's quake was said to have filled a "seismic gap" where a large tremor had been expected for sometime. Attention has now turned to the far north of the country, where there is a similar expectation of significant seismic event in the next 10 to 20 years.

The country needed to be better prepared, said Raul Madariaga a Chilean seismologist who is a professor at the Ecole Normale Superieure in Paris, France.

"Chile has no national seismic network; there is only a small network maintained by a university department in Santiago," he told BBC News.

"There is no national organisation that takes care of earthquakes and this has proved to be a big embarrassment, mainly to the government because six hours after the earthquake they couldn't tell the population whether a tsunami was going to occur even though the tsunami had already happened."

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