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How might a large moving body like a continent look, both along its forward moving edge and its trailing edge?
Obtain maps of the eastern and western portions of the United States and trace the shoreline along both coasts.
and discuss similarities and differences between coastlines. (You should
find a relatively straight Pacific coastline and a highly irregular Atlantic
The northern portion of the western edge, (the forward moving edge of the North American plate), is thought to be ramming against and riding over the eastern edge of the Pacific Ocean floor.
The Pacific plate bordering the San Andreas Fault, however, is moving north and west, while the North American Plate is moving south. This fault is a very high-stress fault. Relieving its' stress caused the great San Francisco Quake of 1906, which measured 8.3 on the Richter Scale.
(The State of California, U.S.A., is thickly underlain with faults, and there are over 1,000 earthquakes in California each year. Most of them are very weak; many of them are in uninhabited areas; therefore, very little damage is caused in the small quakes.)
The eastern edge of the Continental Plate is dipping and trailing behind; following the moving edge just because it is attached.
Two bricks on blocks can be used to demonstrate how the North American Plate might be riding over the Pacific Ocean Plate at the subduction zone.
As the bricks are moved, breakage occurs in the boundary zone between the two blocks, and internal stresses in the earth build up and are periodically released as earthquakes.
Keep in mind, however, that the Pacific Ocean Plate is not one plate in the shape of the entire ocean, and the North American Plate is not just one big plate in the shape of the continent.
What do you think it is that causes the plates to move?
Plate tectonics is a most interesting field of study, about which more is being learned almost daily.
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