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Plate Tectonics.

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Introduction

Plate Tectonics These lines on this map show us where all of the mid-ocean ridges are and form all of the tectonic plate boundaries on which the continents are situated. This cross section shows us how all of the volcanoes are situated on top of a plate boundary. The map on the previous page shows us what we call the "ring of fire" and this shows us how all volcanoes are situated on a plate boundary except for a few which are situated away from the plates. This map shows us the major plates and gives all of their names. The earth is made of about six large plates with a number of smaller ones. Tectonic plates, sometimes named lithospheric plates are large irregular shaped slabs of oceanic or continental crust. Oceanic plates and continental plates differ in a fundamental way which gives rise to their appearance over the face of the planet. Continental plates also are much thicker at about 100km deep to balance the height of mountains whereas oceanic plates tend to be about 5km deep. The plates are constantly moving but at a very slow rate. How fast are these plate boundaries moving? One way to tell is to measure their rate of movement, which scientists can now do with some accuracy using satellite global positioning systems, or GPS. ...read more.

Middle

This can create earthquakes and destroy large buildings. On January 25, 1999 a 6.2 magnitude quake near the city of Armenia, Columbia, for example, killed an estimated 1,185 people and injured some 4,750. About 60% of all buildings were destroyed. Many burned to the ground. We are trying to stop structural damages as repairs cost millions by installing large shock absorbers. One cost-effective strategy for limiting the effects of a major quake would be to provide earthquake protection kits, seismic upgrades and retrofits to older buildings. Nickel-containing stainless steels resist corrosion, are fire-resistant and have a higher tensile strength and greater elongation than ordinary steel, all of which renders them well suited to solving problems related to earthquakes. For example, the outstanding plastic deformation capability of stainless steel and its ability to absorb a tremendous amount of energy has proved advantageous when used in space trusses, bracing, column bases and base-isolated structures. We know plates move as all of the continents seem to be like a large jigsaw and the same animals and plants are found where they used to be connected. Scientists believe that plates move due to convection currents in the magma of the earth. This is quite similar to lava lamps. ...read more.

Conclusion

We now know that the farther away you travel from a ridge, the older the crust is, and the older the sediments on top of the crust are. The clear implication is that the ridges are the sites where plates are moving apart. The model of the Earth developed by the seismologists, at this time, was a liquid iron core surrounded by a solid mantle with no convection movements. When Elsasser and Bullard (1965) developed their geomagnetic field theory, postulating that there are convective motions in the fluid iron core, there was no real objection by the seismologists since the core did not transmit s-waves, indicating it is a classical fluid. It was not until the development of paleomagnetism that there was new evidence for continental drift, then later on, geophysical measurements of the ocean floor swept away most of the doubts geophysicists had about continental drift. This now constitutes part of the subject called plate tectonics. Many theories on the mechanism for plate movement have been developed. The most popular and widely held view is that convection currents below the lithospheric plates, in the mantle, are responsible for their movement. This involves hot spots and subduction zones. The most radical view was that that developed by Carey (1954), Heezen (1959) and others, that the earth is expanding causing the continents to break up and form plates. ...read more.

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