Friday, February 25, 2011

[Geology2] N.Z. Shows Even Strong Building Codes Are No Match For EQ

New Zealand shows even strong building codes are no match for monster earthquake, experts say

Los Angeles Times
February 25, 2011 |  8:32 am

The devastation and loss of life in the Christchurch, New Zealand, quakes offer some sober lessons for California, earthquake experts said.The damage shows that a sharp earthquake in a highly vulnerable area can get the better of strong seismic safety codes.

"If the dart lands right on you, it generates intense shaking and a lot of buildings that we think are safe turn out to not be safe," said Susan Hough, seismologist with the U.S. Geological Survey.

The quake's epicenter occurred less than six miles from the center of Christchurch, New Zealand's second-largest city, far closer than a 7.0 quake in September, which had an epicenter about 30 miles away and resulted in no deaths.

 Also, the highest ground acceleration recorded was greater than 2G, or twice the acceleration of gravity –- which would make Tuesday's quake among the most powerful in terms of ground-shaking acceleration on record, said Hough. It was strong enough to throw objects in the air.

"There's only a handful of records of shaking" as strong as 2G, Hough said. "That's quite extreme shaking.… Some earthquakes just have stronger shaking that affects buildings."
By contrast, the ground shaking in the 6.7 Northridge quake in 1994 was less, recorded at 1.7G, Hough said. Hough has estimated that the strongest ground shaking in Port-au-Prince in the Haiti earthquake in 2010 was only about 0.5G.


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