Earthquakes
You might remember being in an earthquake- the ground rumbles and shakes, lamps begin to sway back and forth, shelves begin to rattle and spill out their contents, the floor and the walls begin to shake. Even if you don't remember being in an earthquake, you have lived through thousands of tiny earthquakes during your lifetine. The earth is always constantly creating earthquakes. Earthquakes are among the most devastating natural events that occur on Earth and are a reminder that our planet is dynamic and changing.
An earthquakes is the earth's shaking caused by pieces of the crust of the earth that suddenly shift. The crust (the thin outer layer) is mostly a brittle and cold rock compared to the rock deep inside. The most common cause of earthquakes is faulting. A fault is a break in the earth's crust when movement occurs. The study of this movement is known as plate tectonics.
Most earthquakes occur in narrow belts along the boundaries of crustal plates, usually where the plates push together or slide past each other. Sometimes plates are locked together, unable to release accumulating energy. When the energy grows stong enough, the plates will break free. When two pieces are together and get pushed in different directions, they will stick together for a long time (probably many years), but eventually the forces pushing on them will force them to break apart and move. This sudden shift in the rock shakes all the ground around it and that's what you feel when it occors.
There are three types of plate boundaries: spreading zones, subduction zones and transformation faults. At spreading zones, molten rock rises, pushing two plates apart and adding new material at their edges. Most spreading zones are found in oceans; for instance, the North American and Eurasian plates are spreading along the mid- Atlantic ridge. Spreading zones usually have earthquakes at shallow depths (within 30 kilometers of the surface).
Subduction zones are found where one plate slides over the top pushing it downward into the mantle where it melts. Along the northwest coast of the United States, western Canada, southern Alaska and the Aleution Islands are an example of a subduction-zones. Characterized by deep-ocean trenches, shallow to deep earthquakes, and mountian ranges containing volcanoes are the Subduction zones.
Scientists predict greater damage from earthquakes.