Mexico quake amongst largest intermediate-depth earthquakes ever recorded

Earlier today, a massive earthquake hit Mexico rattling the country’s capital and killing dozens of people. Geoff Abers, an expert of earthquake seismology and a professor of geophysics at Cornell University, says current estimates of an 8.2-magnitude makes this among the largest intermediate-depth earthquakes ever recorded.

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Abers says:

“This is an ‘intermediate-depth’ earthquake, centered about 70 km (45 miles) deep within the earth. Faults for earthquakes like this generally do not reach the earth’s surface and preliminary modeling of the signals indicates rupture extends no more than about 20-40 km shallower – these numbers are still very uncertain.

“Earthquakes happen in places like this because tectonic plates subduct and while they are still somewhat rigid they are bending as they go down. The actual physical mechanism that makes earthquakes at these depths is still rather controversial, as ‘normal’ earthquake physics models tend to break down this deep.

“The 8.2-magnitude earthquake (the best current estimate) makes this among the largest intermediate-depth earthquakes ever recorded. I believe it is one of the 5 largest in the last 40 years.

“Because it is so deep, it is surprising that there is a tsunami alert and some preliminary indications of a tsunami. Tsunami’s usually are generated when earthquakes rupture the sea floor, such as off Japan in 2011. We should know more in the next couple of hours as to how real this threat is.

“Because it is so deep, and centered offshore, the strongest shaking is not as strong as it would be if an 8.2-magnitude were very shallow. But, the somewhat-strong shaking is felt over a much larger area and because the earthquake is so large there is potential for significant damage. Shaking is predicted to be strong enough to cause damage to ‘unreinforced’ structures over a large part of southern Mexico and Guatemala.”

 

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