Haiti-sized earthquakes occur multiple times each year

Thursday, March 4, 2010 | 12:01 a.m. CST; updated 9:30 a.m. CST, Thursday, March 4, 2010

The Haitian earthquake was the result of two plates sliding past each other in opposite directions along a transform fault. This was incorrectly described in an earlier version of this story.

COLUMBIA — Earthquakes of the magnitude of the one that devastated Haiti are statistically common, an MU geologist says.

“Earthquakes like the one in Haiti are very common and rarely make it into the headlines, but in this case, the dense population and poor construction turned that earthquake into a disaster,” said Mian Liu, a professor in the MU department of geological sciences.

The Haiti quake registered as magnitude 7.0. An average of 17 earthquakes with magnitudes of 7.0 to 7.9 occur each year, according to the U.S. Geological Survey Web site. But they often occur in sparsely populated areas, Liu said.

The magnitude of the suffering in Haiti was far from common. The quake on Jan. 27 killed more than an estimated 222,000, injured 300,000 and displaced 1.1 million people, according to the survey.

In contrast, an 8.8-magnitude quake such as the one Saturday in Chile happens on average less than once a year, Liu said. Although official estimates for the Chilean quake are unavailable, a Reuters article pegged the Chilean death toll at about 800 as of Wednesday.

The 1.8-point difference between the magnitudes of the two quakes might not sound like much, but the impacts are substantial.

“The difference in energy release is huge," Liu said. "The Chilean earthquake was over 500 times greater than the earthquake in Haiti."

The difference, which should have meant devastation for Chile, was balanced out by Chile’s preparedness and structural stability.

Most earthquakes occur on the boundaries of tectonic plates, which are strong, rigid pieces of the Earth’s top layer, Liu said. The plates constantly move relative to each other, and when they move against each other along the boundaries, “that’s where they cause trouble," Liu said.

The Haitian earthquake was the result of two plates sliding past each other in opposite directions along a transform fault. Chile’s earthquake is classified as a subduction quake, Liu explained, which is caused by one tectonic plate moving underneath another.

Although scientists constantly search for clues to help predict earthquakes, Liu said that currently the only thing they can do is look back and examine earthquakes to make generalizations.

“The scientific community doesn’t have any reliable method for prediction," Liu said. "That’s still out of reach for us.”

Based on Chile’s geography and past seismic activity, however, Liu said he wasn’t surprised to hear about the earthquake in Chile; the strongest recorded earthquake with a magnitude of 9.5 happened in Chile in 1960.

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MOSA MONKU March 4, 2010 | 3:30 a.m.


(Report Comment)
Glenn Rice March 4, 2010 | 10:20 a.m.

The Richter scale is logarithmic, which means that a 1-point increase is 10 times more energy, and a 2-point increase is 100 times more. Where does Liu come up with the "over 500 times" figure?

(Report Comment)
Glenn Rice March 5, 2010 | 10:25 a.m.

Seriously Missourian, are you going to correct this error? The Chilean earthquake was about 50x the energy of the Haiti earthquake -- not 500x.

(Report Comment)
Glenn Rice March 5, 2010 | 10:36 a.m.

Hey, I'm wrong and the physics guy is right. I'm looking at amplitude. Energy release scales differently (greater). Never mind!

(Report Comment)

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