July 22, 2009

Huge Earthquake Inches NZ Closer To Australia

A recent 7.8 earthquake in New Zealand actually moved the country closer to Australia, scientists said Wednesday.

The two small countries are separated by the 1,400-mile-wide Tasman Sea, which means the 12-inch scoot in New Zealand's southwest will not make too much of a difference.

However, according to earthquake scientist Ken Gledhill, the shift reveals the phenomenal force of the tremor.

"Basically, New Zealand just got a little bit bigger is another way to think about it," he told AFP.

He said that the southwest of the South Island may have moved about 12-inches closer to Australia, but the east coast of the island moved less than an inch toward the west.

This quake marked the biggest New Zealand has seen in 78 years, but it still only caused slight damage to buildings and property when it struck last Thursday in the remote southwest Fiordland region of the South Island.

The earthquake generated a small tsunami, with a tide gauge on the West Coast of New Zealand recording a wave of 3-feet.

"For a very large earthquake, although it was very widely felt, there were very few areas that were severely shaken," Gledhill said.

An inspection of the forested fiords near the quake's epicenter spotted only a few landslips or other signs of damage.

The reason that there was so little evidence of damage is because the type of rupture that took place at the boundaries of the Australian and Pacific plates caused the energy from the quake to be largely directed westwards towards the sea rather than inland towards the nearest towns.

The quake is a type known as a subduction thrust rupture, which also means that the quake produces a lower frequency of shaking. It is felt as more of a rolling motion than sharp damaging jolts.

Earthquakes are very common to New Zealand because it is the meeting point of the Australian and Pacific continental plates.

According to Gledhill, the most recent quake might have conjured a major quake on the offshore section of the Alpine fault, off the coast of Fiordland in the Tasman Sea.

"There could easily be another large earthquake in another part of that region. We can't predict that obviously."

The last quake of this magnitude was in February 2, 1931 when a 7.8 quake claimed at least 256 lives in the North Island city of Napier.

The biggest quake that has ever been recorded there was in the year 1855. It measured 8.2 and severely damaged the early European settlement that later became the capital Wellington.

It was very odd for the latest quake to have struck directly on the boundary of the Australian and Pacific plates and will be important in researching earthquake hazards, according to Gledhill.

Image Courtesy Jacques Descloitres, MODIS Land Rapid Response Team at NASA GSFC