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| November 2009 |
| Billie Silvey |
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| Geology |
| Someone may say of a deal or an organization, “It’s as solid as the earth beneath your feet.” That may be reassuring to some people, but I live on the Pacific Rim where the earth isn’t always such a solid thing. Here in Los Angeles, we’re threatened by earthquakes along the San Andreas Fault, the line where the Pacific Plate meets the North American Plate. There’s a good bit of friction there. The land west of the fault lies on the Pacific Plate, which is moving slowly to the northwest. The land east of the fault is moving southwest, with a rate of slippage that averages approximately one and a third inches a year. The westward motion of the North American Plate creates compressional forces which create the Coast Ranges. The northwest motion of the Pacific Plate creates significant compressional forces where the North American Plate stands in its way, creating the Transverse Ranges in Southern California. How do I know? Geologists, who study of the history of our planet--the materials it’s made from, the structure of those materials, and the processes acting on them—told me so. Geologists study processes such as landslides, earthquakes, floods and volcanic eruptions so people can avoid risk. They map areas which have been affected by natural disasters to help prepare for new ones in the future. They study the materials of the earth, including oil, metals and water. They locate rocks that contain important metals and plan mines to produce them and methods to extract them. They also study earth’s history. For instance, by understanding how climate has changed in the past, they can better understand how our climate is changing today and what the results might be. And by studying earthquakes in the past, they can better predict what might happen the next time the pressure builds and things start moving on the fault. The earth is less stable than we might think, because it’s in three parts. The land we stand on is part of the crust, the outermost solid silicate shell which is chemically distinct from the underlying mantle. The mantle is about 1,800 miles thick and constitutes about 84 percent of Earth's volume. The mantle is a slow-moving, highly viscous layer that separates the crust and the solid core, which occupies about 15 percent of Earth's volume. So, next time someone tries to sell you on a deal that's as solid as "the earth beneath your feet," take warning. Sometimes, at least around here, the earth moves. |
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