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Chapter Earthquake
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Answer:
In seismology, a seismic zone or seismic belt is an area of seismicity potentially sharing a common cause. It may also be a region on a map for which a common areal rate of seismicity is assumed for the purpose of calculating probabilistic ground motions. An obsolete definition is a region on a map in which a common level of seismic design is required.
Most earthquakes occur along the edge of the oceanic and continental plates. The earth's crust (the outer layer of the planet) is made up of several pieces, called plates. The plates under the oceans are called oceanic plates and the rest are continental plates. The plates are moved around by the motion of a deeper part of the earth (the mantle) that lies underneath the crust. These plates are always bumping into each other, pulling away from each other, or past each other. The plates usually move at about the same speed that your fingernails grow. Earthquakes usually occur where two plates are running into each other or sliding past each other.
Along Faults
Earthquakes can also occur far from the edges of plates, along faults. Faults are cracks in the earth where sections of a plate (or two plates) are moving in different directions. Faults are caused by all that bumping and sliding the plates do. They are more common near the edges of the plates.
Types of Faults
Normal faults are the cracks where one block of rock is sliding downward and away from another block of rock. These faults usually occur in areas where a plate is very slowly splitting apart or where two plates are pulling away from each other. A normal fault is defined by the hanging wall moving down relative to the footwall, which is moving up.
Reverse faults are cracks formed where one plate is pushing into another plate. They also occur where a plate is folding up because it's being compressed by another plate pushing against it. At these faults, one block of rock is sliding underneath another block or one block is being pushed up over the other. A reverse fault is defined by the hanging wall moving up relative to the footwall, which is moving down.
Strike-slip faults are the cracks between two plates that are sliding past each other. You can find these kinds of faults in California. The San Andreas fault is a strike-slip fault. It's the most famous California fault and has caused a lot of powerful earthquakes.
FIGURE 4 - TWO STRIKE-SLIP FAULTS. (LEFT), A LEFT-LATERAL STRIKE-SLIP FAULT. NO MATTER WHICH SIDE OF THE FAULT YOU ARE ON, THE OTHER SIDE IS MOVING TO THE LEFT. (RIGHT), A RIGHT-LATERAL STRIKE-SLIP FAULT. NO MATTER WHICH SIDE OF THE FAULT YOU ARE ON, THE OTHER SIDE IS MOVING TO THE RIGHT.
Explanation:
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The World's Major Earthquake Zones
Seismic Hazard Map of the World . The result was the most accurate map of global seismic activity to date. ...
North America . There are several major earthquake zones in North America. ...
→ South America . ...
→ Asia . ...
→ Europe . ...
→ Africa . ...
→ Australia and New Zealand . ...
→ Antarctica . ...
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What is a seismic zone?
A seismic zone is used to describe an area where earthquakes tend to focus; for example, the New Madrid Seismic Zone in the Central United States. A seismic hazard zone describes an area with a particular level of hazard due to earthquakes.
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Why are some places more at risk of earthquake than others?
Perhaps the most significant factor determining why some places suffer more than others is the tectonic location of an area. The distribution of earthquakes is commonly linked to the margins of global plates. Whilst the assertion that earthquakes only occur at plate margins is broadly true, it would be overly simplistic to assume that earthquakes are more common, and more devastating at some margins than at others.
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