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Earth Sense: Quakes will continue as Earths plates keep shifting
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“What’s becoming of the world? When will it all end?” Words of my late grandmother came to mind after the Oct. 14 quake off the coast of Nicaragua and El Salvador.

It won’t end, actually. Even major quakes like this recent one, registering 7.1 on the Richter scale, are a common event in the Earth’s fault zones.

They don’t represent a new development, and aren’t even caused by the popular general culprit, human activities. Earthquakes occur somewhere every day.

It’s easier to understand if you visualize the globe not as a solid sphere made of hard rock (and preferably not as a flat pancake, either). It’s a ball of mostly molten minerals, with a very thin hardened crust on top.

Where it’s covered by oceans, that crust is thinnest. In the deep basins of the Atlantic and Pacific, there can be as little as 6 miles before conditions get gooey farther down.

Here, at the foot of the Georgia Mountains, the Earth’s crust is approximately 28 miles thick, providing a reasonably solid foundation. That’s part of the reason why large earthquakes are rare in our area.

The other reason is that we’re not near a place where the puzzle pieces of Earth’s outer skin come together. Nicaragua, El Salvador, Honduras and other Central American nations are.

Geologically, the Caribbean is a very complex system of plates (the puzzle pieces) and faults (their contact zones). The Caribbean Plate is joined by four others: North American, South American, Nazca and Cocos Plates.

With that much heaving and shoving underground, it’s fortunate that the October quake didn’t turn out like the 1972 one, when 90 percent of Managua, Nicaragua’s capital, was destroyed and 6,000 people were killed.

Besides normal plate boundaries, subduction is a big trouble maker. That’s what happens when a thin plate, like the Pacific one, gets pushed underneath a thick one, for example the American Plate along the Alaskan Coast. It’s like reaching under a lumber pile with a prybar and shoving hard.

The 1964 quake in Anchorage was one of the strongest ever recorded. Volcanic eruptions like Mount St. Helens, or prehistoric ones at Mount Rainier, Mount Hood, Mount Shasta and others have been associated with the process of oceanic crust being shoved deep under the American Plate.

These processes won’t stop. Central America and western North America will keep producing news about earthquakes.

Rudi Kiefer, Ph.D., is a professor of physical science and director of sustainability at Brenau University.

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