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Australia's tsunami system performs well

bondi beach

Last night's tsunami had little effect on Australia's coast (Source: Reuters)

Last night's tsunami warning for south-eastern Australia, may have come to nothing, but it did demonstrate the worth of the monitoring system, says one expert.

The warning was announced soon after an earthquake, measuring 7.8 on the Richter scale, occurred off the south coast of New Zealand's South Island.



Ryan says the tsunami that followed only warranted a 'marine threat' warning with waves rising 30 centimetres at Port Kembla, near Wollongong and no significant damage has been reported.


He says the Puysegur subduction zone is a region where Australia's tectonic plate pushes underneath the Pacific plate.

Predicting severity

Ryan says the scale of an earthquake is the main factor that influences a tsunami's severity.

"That's where the energy comes from initially."

Ryan says a tsunami is generated by an earthquake that ruptures the sea floor and disturbs the surface water of the ocean.

He says tsunami waves have unusually long wavelengths.

"Rather than go up and down in a few seconds they go up and stay up for as long as 15 minutes. It's more like a temporary rise in sea level."

Ryan says when tsunami waves reach shallow water the front of the waves slow down.

"But the section following the front waves keeps pushing in and the wave rises higher and higher, and that's why we see the really damaging effects on the beach."

The location of the continental shelf and the shape and angle of the sea floor leading up to the beach will also affect how the tsunami waves build before they hit land, says Ryan.

Test for new warning system

After an earthquake has been recorded Australia's Tsunami Warning Centre uses models to predict the severity of a tsunami and issue appropriate warnings.

Ryan says the tsunami warning system, which was upgraded after the 2004 Boxing Day tsunami, worked efficiently.

Since the Boxing Day tsunami Australia's warning system has been upgraded to a two tier system.

"Now we can warn people about small tsunamis, like last night, says Ryan. "We need to warn people about these because they can cause strange currents."

This type of tsunami generates a marine threat warning.

"The second level is for big tsunamis that may inundate the land and require evacuations," says Ryan.

Although Australia's tsunami warning system is one of the best in the world, Ryan says the system is still pretty new and there is always room to improve the model.

Tags: earthquake, tidal-wave, earth-sciences, geography, geology