An 8.2 magnitude earthquake that struck southern Mexico last year has baffled scientists as it broke a tectonic plate. The Tehuantepec quake had struck off the Pacific coast of Mexico's Chiapas state, which borders Guatemala. Approximately 100 people were killed with hundreds more being injured. Geologists had initially thought that the earthquake occurred where the Cocos ocean plate is being overridden by a continental plate. Mega quakes generally occur near the top of where plates converge, which is known as the subduction zone. The epicentre of the Tehuantepec quake was, however, much deeper at about 28 miles in the Cocos plate than predicted by earthquake models, a report stated in the journal Nature Geoscience.
The study also showed that the Cocos plate has been completely split apart due to the earthquake. “If you think of it as a huge slab of glass, this rupture made a big, gaping crack,” Diego Melgar, lead author of the study explained. “All indications are that it has broken through the entire width of the thing,” he further added. Melgar's team suspects that seawater got into the Cocos plate possibly sped up the cooling, making it susceptible to tension earthquakes. If that did occur, Melgar stated, that other areas including the U.S. West Coast and Guatemala southward in Central America are susceptible to tension-zone earthquakes. “Our knowledge of these places where large earthquakes happen is still imperfect,” Melgar stated, further adding, “We can still be surprised. We need to think more carefully when we make hazard and warning maps. We still need to do a lot of work to be able to provide people with very accurate information about what they can expect in terms of shaking and in terms of tsunami hazard.”
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