The Haiti and New Zealand Quakes: A Fair Comparison?

Analysis by Michael Reilly

At first blush, the earthquake that struck Christchurch, New Zealand on Saturday was the spitting image of the one that ravaged Haiti in January. Each was a powerful magnitude 7.0 quake, and each occurred on a strike-slip fault near a major population center.

New Zealand orbit The similarities end there. Reports out of Christchurch have been almost miraculous: Though the city suffered extensive damage, not a single person out of nearly 400,000 appears to have died. By contrast, the Haitian capital city of Port-au-Prince was flattened, and a quarter of a million people were killed. There remains immense suffering in the country, nearly eight months later.

There are two main reasons for this extreme contrast in events: luck, and preparedness.

First, a closer look at the two quakes reveals an important geological difference. The epicenter of the Haiti quake was just 16 miles from downtown Port-au-Prince, while in Christchurch the tremor struck more than 30 miles away.

“Seismic waves are just like sounds waves,” Peter Yanev, a structural engineer with California-based Risk Solutions International told Discovery News. “Strong ground motion dies out with distance.”

He added that even though Christchurch is built on weak soil that can amplify shaking during an earthquake, he suspects much of the worst of the seismic energy had dissipated by the time it reached the heart of the city.

New Zealanders were also lucky because they were at home, asleep in houses built up to the country’s stringent building codes when the quake hit at 4:35 a.m. local time. “The old buildings downtown were the ones that got beat up, which is what you’re seeing all those pictures of,” Yanev said. “There’s some luck involved that people weren’t around when parapets were falling off buildings.”

And of course, there are the building codes themselves. Straddling the boundary of the Australia and Pacific tectonic plates, New Zealand regularly experiences powerful, damaging quakes, and the government has made certain that all modern buildings are built to withstand strong shaking.

In Haiti, there are no building codes to speak of.

“There are basically four places in the world — California, Japan, Chile, and New Zealand — that are serious about earthquake design, and that’s it,” Yanev said.

Of course economic standing has a lot to do with it; New Zealand is far better off than chronically-impoverished Haiti.

But Yanev said that even in regions known for their preparedness, Christchurch’s success story shouldn’t be cause for complacency.

“There is still a danger that people will get cocky. They look at buildings performing well in a situation like in Christchurch and they think ‘we’re good,’ but no, we’re not,” he said.

In the future, more powerful quakes than New Zealand’s latest will strike on the San Andreas fault in southern California, the Heyward fault in the San Francisco Bay Area, or along the Cascadia fault near Seattle and Vancouver, as well as in many other regions of the world. Their epicenters will be closer to city centers, and the shaking they cause could exceed even the most modern building codes.

These scenarios are, unfortunately, not a question of “if”, but “when”.

Image: (New Zealand from orbit, looking North. Large valleys on the South Island are surface expressions of major faults) NASA via Te Ara

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