Seismologist: What caused Mexico's earthquake
Another deadly earthquake struck deep under Mexico.
Shortly after noon on Tuesday, an earthquake violently shook the area around Mexico City, collapsing numerous buildings into dust, killing more than 100. The greatest impact was in densely populated Mexico City, but the shaking was even more intense in Puebla, closer to the epicenter.
The shaking energy was generated at the earthquake's source, 30 miles deep, for just 20 seconds, but the waves reverberated for much longer, up to a minute or two, in the mountain and valleys.
Plate tectonics was the engine behind the shaking, as is true for all major earthquakes. Along the coast of Mexico, the Cocos Plate slides underneath the North American Plate, moving about three inches per year. Tuesday's earthquake, however, was caused by crumpling arising from the downward bending of the sinking Cocos Plate, rather than directly by slippage between plates.
A similarly deep but much larger magnitude 8.1-earthquake struck two weeks ago, also from the crumpling of the Cocos Plate. It struck Mexico 400 miles to the southeast and offshore, not far from Guatemala, and killed dozens of people. It is not immediately clear whether Tuesday's earthquake was triggered by the earlier one or if it is unrelated -- usually aftershocks are not so distant in time.
In the history of Mexican earthquakes, Tuesday's was coincidentally the 32nd anniversary of the 1985 Michoacan earthquake, which resulted in thousands of deaths.
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