Thu, Feb 24, 2011 - Page 4 News List

NEW ZEALAND EARTHQUAKE: ‘Bullseye’ quake caused extensive damage: scientists


Christchurch in New Zealand weathered a magnitude 7.0 earthquake, but a smaller 6.3 aftershock toppled buildings and killed scores largely because it was a “bullseye” direct hit, scientists said.

Tuesday’s cataclysmic tremor, which left nearly 400 people dead or missing and the city center in ruins, was so close to the city of 390,000 and so shallow that major damage was inevitable, they said.

“This quake was pretty much a bullseye,” said professor John Wilson, deputy dean of engineering at Australia’s Swinburne University of Technology. “It was quite a large 6.3-magnitude event and so close to Christchurch that we weren’t surprised to see significant damage. At that close range, the level of shaking is quite severe.”

The earthquake struck six months after a violent magnitude 7.0 tremor damaged 100,000 buildings and left a major repair bill, but caused no deaths, after striking overnight on Sept. 4, when most people were safely in bed.

However, Tuesday’s tremor hit at the worst possible time, at lunch on a weekday, when offices were open and streets were busy with shoppers who were vulnerable to falling masonry. Its epicenter was only 5km from the city at a depth of just 4km below the land’s surface, meaning there was little ground to absorb the blow.

Some of the worst-hit buildings — including Christchurch’s landmark cathedral, which lost its spire — were historic structures in the city’s heart.

However, newer office blocks such as the CTV and Pyne Gould buildings collapsed, while the towering Grand Chancellor Hotel was tottering dangerously. New Zealand buildings have been designed to resist earthquakes since the 1970s.

David Rothery of the Volcano Dynamics Group at Britain’s Open University said the soft ground on which the city is built would have magnified the shaking, making the magnitude 6.3 quake even more deadly.

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