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jueves, 28 de mayo de 2009

Caribbean Quakes & Complications

There was a major earthquake offshore of Honduras today. At 7.1 magnitude, it packed enough punch to endanger lives and warranted a brief tsunami watch for Belize, Honduras anHonduras7-1Mquaked Guatemala -- the countries with coastlines closest to the epicenter. It's an interesting quake in other ways.

The Caribbean is a complicated place when it comes to earthquakes. I'm no expert on the matter, but a look at a geologic map shows that it's crisscrossed with faults of all kinds, which form the edges of a jumble of broken plates in Earth's crust there. All these shards of plates are crammed together and jostling for space by the much larger, more powerful plates all around them, which are going about their much larger-scale tectonic business.

The most dangerous of the faults tend to be those created by plates colliding in a frontal assault -- where one is pushed under another in what's called subduction. This is the sort of situation you see in Sumatra and southern Alaska -- among the world's most quaky places. There is some of this going on in the northeastern Caribbean, but that's not what caused this quake way over in the western part of that sea.

W-carib-map The culprit today is more like the infamous San Andreas Fault in California, created by two pieces of the Earth's crust grinding side-by-side and in opposite directions. You can see which fault it was on this GSA geologic map I just pulled out and photographed (at left). I inserted a little "X" at the epicenter near the center of the image. The black lines are the faults.

Among other things, the side-wise movement of the plates in this corner of the Caribbean is the cause of that deep purple spreading center in the upper right-hand side of the map image. The crust is being pulled apart in that area. Just another complicated day in the Caribbean.

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