- Associated Press - Tuesday, February 22, 2011

LOS ANGELES (AP) - The latest New Zealand earthquake is five times smaller than the one that rocked the area last September yet caused much more destruction.

Why? Scientists say it’s all about location, location, location.

Tuesday’s magnitude-6.3 quake was centered about 3 miles (5 kilometers) from the populated hub of Christchurch, toppling buildings and killing dozens.

The location, the timing during the middle of a work day and the quake’s shallow depth of 3 miles (5 kilometers) combined to make a deadly mix.

The jolt “is squarely beneath the city itself,” said seismologist Egill Hauksson of the California Institute of Technology. “All the old historic buildings are being shaken more violently than they were built to withstand.”

Scientists classified it as an aftershock of the powerful magnitude-7 that struck last Sept. 4.

No one died in that early morning quake _ which released 11 times more energy _ mainly because it was centered farther away, about 30 miles (48 kilometers) west of the city center. It was also twice as deep as Tuesday’s aftershock. Shallower quakes tend to be more damaging.

While New Zealand has strict building codes, Christchurch has a number of pre-World War II buildings that were badly damaged by the September quake, which also triggered landslides in the area.

Another reason why this latest quake was more deadly is because buildings that were previously weakened by ground shaking were more likely to suffer damage or even collapse this time around, said Tom Jordan, who heads the Southern California Earthquake Center.

Since September, about half a dozen aftershocks greater than magnitude-5 have rattled Christchurch. Tuesday’s is the largest aftershock to date.

“You can have an aftershock months after the main shock,” said geophysicist Paul Earle of the U.S. Geological Survey in Golden, Colorado. “Just because a few months have gone by doesn’t mean you can’t have a large, damaging earthquake.”

___

Online:

U.S. Geological Survey: https://earthquake.usgs.gov/


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