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  ABC News 4 Apr 07
Barrier Reef could have blocked tsunami: scientist

National Geographic 2 Apr 07
Deadly Tsunami Sweeps Solomon Islands
Richard A. Lovett for National Geographic News

A large tsunami crashed into low-lying portions of the Solomon Islands northeast of Australia yesterday, killing at least 13 people. About 500 homes were destroyed, and the death toll is expected to rise. Reports put the waves' size between 10 and 16 feet (3 and 5 meters).

The tsunami was triggered by a large earthquake, magnitude 7.6, centered 215 miles (345 kilometers) northwest of the islands' capital of Honiara. The earthquake struck at 7:39 a.m. local time Monday morning, and the waves hit soon afterward, washing as far as half a mile (0.8 kilometer) inland.

The quake occurred at the boundary where three tectonic plates collide with the large Pacific Plate at an average velocity of about 4 inches (10 centimeters) a year.

The tectonics of the region are extremely complex, said Emile Okal, a geophysics professor at Northwestern University. "It is a very active area," Okal said. "There are earthquakes there all the time."

However, he added, "to my knowledge this is the biggest [earthquake] in that particular section--in probably 100 years."

Australia Escapes Destruction

The quake's epicenter was extremely close to the surface, centered only 6 miles (10 kilometers) below the seafloor, the U.S. Geological Survey reported on its Web site.

This may have contributed to the formation of the tsunami, Okal said. There is some evidence that shallow earthquakes produce greater seafloor vibrations than deeper ones do, he explained.

But this does not explain why other regions appear to have been spared the tsunami's effects. Tsunamis generally propagate most strongly in a direction perpendicular to the fault zone, which in this case should have sent a wave toward Australia, Okal said.

Although the Australian government closed beaches for many hours, the tsunami did not strike there.

Okal suspects that Australia was protected by the Great Barrier Reef, a ridge at the tip of Papua New Guinea. But it will take some time to determine why this happened, he said, because the interaction between tsunamis and shallow underwater landforms is very difficult to calculate.

Although full casualty reports have yet to be released, Okal noted that, given the size of the wave and the number of houses destroyed, the death toll appears to be remarkably light.

"If [the death toll] stays within this order of magnitude, this is nothing short of a miracle," he said. "There are reports saying that the people felt the earthquake and ran away from the beach, which is exactly what they are supposed to do," he added.

Overall, however, there is a need for continued tsunami awareness, Okal said. "We get a tsunami like this pretty much every year, and occasionally two a year or so," he said.

ABC News 4 Apr 07
Barrier Reef could have blocked tsunami: scientist

A Queensland marine scientist says the Great Barrier Reef may have delayed the impact of the tsunami that was generated in the Solomon Islands on Monday.

Dr Rob Beaman filmed three waves which caused the sea level off Cairns to rise by around 20 centimetres on Monday morning. He believes the waves were a delayed and small-scale impact from the earthquake and ensuing three-metre tidal wave in the Solomons.

Dr Beaman says the waves arrived nearly 30 minutes later than predicted and he believes the Barrier Reef could be the reason.

"It would need some modellers with some very fancy computers to be able to work it out exactly," he warned. "The arrival time is based on modelling that is done at the Pacific Tsunami Warning Centre and they may have to fine-tune that somewhat for future tsunami predictions."

Dr Beaman says the first impact he filmed at Yorkeys Knob marina was followed by two other waves which churned up the bottom of the marina and turned the water a murky brown.

"When that second pulse came through it was amazing. I almost had to pinch myself to believe it because I could really easily see this big line of brown water moving into the marina," he said. "This is an ebbing tide, the water should be moving out, but it was coming in."
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Related articles on Global: marine issues and tsunami and the environment
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