7.4 quake rocks southern Mexico, shakes capital

In Mexico City, a Los Angeles Times reporter writes that "there was an initial rocking, a pause and then a much stronger, sustained rocking motion that swayed buildings in many parts of the capital."

A BBC reporter estimated that the earth shook for about a minute, a virtual eternity to people experiencing a big quake. But that's nowhere near the longest shaking ever recorded. That record is held by the December 2004 quake off Sumatra, Indonesia. Scientists determined that the magnitude-9.1 rupture, which generated huge tsunamis and killed more than 283,000 people, shook for almost 10 minutes.

"Normally, a small earthquake might last less than a second; a moderate sized earthquake might last a few seconds. This earthquake lasted between 500 and 600 seconds," said Charles Ammon, associate professor of geosciences at Penn State University, according to a CNN report in 2005.

And though big at magnitude 7.4, today's quake does not crack the list of the largest. The March 2011 Tohoku earthquake in Japan registered at magnitude 9.


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