Platetectonics

 

 

 

 

 

 

(understanding this reason of an earthquake)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Scientists now have a fairly good understanding of how the plates move and how such movements relate to earthquake

 

activity. Most movement occurs along narrow zones between plates where the results of plate-tectonic forces are most

 

plain.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

There are four types of plate boundaries:

 

 

 

 

 

 

 

 

 

 

 

 

 

- Divergent boundaries -- where new crust is generated as the plates pull away from each other.

 

 

- Convergent boundaries -- where crust is destroyed as one plate slipes under another.

 

 

- Transform boundaries -- where crust is neither produced nor destroyed as the plates slide horizontally past each other.

 

- Plate boundary zones -- broad belts in which boundaries are not well defined and the effects of plate interaction are

 

unclear

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Divergent boundaries appear along spreading centers where plates are moving apart and new crust is created by magma

 

pushing up from the mantle. (Picture two giant conveyor belts, facing each other but slowly moving in opposite directions as

 

they transport newly formed oceanic crust away from the ridge crest.)

 

 

 

 

 

 

 

 

 

 

 

1.) Perhaps the best known of the divergent boundaries is the Mid-Atlantic Ridge. This submerged mountain range, which

 

strechtes from the Arctic Ocean to beyond the southern tip of Africa, is one part of the global mid-ocean ridge system

 

that encircles the Earth. The rate of spreading along the Mid-Atlantic Ridge averages about 2.5 centimeters per year (cm/yr),

 

or 25 km in a million years. This rate may seem slow by human standards, but because this process has been going on for

 

millions of years, it has resulted in plate movement of thousands of kilometers. Seafloor spreading over the past 100 to 200

 

million years has caused the Atlantic Ocean to grow from a tiny inlet of water between the continents of Europe, Africa, and

 

the Americas into the vast ocean that exists today.