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Earthquakes

The Earth is always moving, usually so slowly that we don't notice. On occasions the earth can move very suddenly, this is called an earthquake. Most earthquakes occur in the earth's crust. The crust covers our earth with layers of rock as deep as 30 feet.

Earthquakes can happen when plates below the Earth's crust push or pull against each other.  This causes the rock to fracture or crack, which is called a fault.  There are different types of faults. One common type is a strike-slip fault. Rocks on one side of this fault try to move past rocks on the other side of the fault which causes energy to build up. Like a super stretched rubber band, rocks will snap past each other causing movement.  A second type, called a thrust or reverse fault, pushes the lower level of older rock above the newer rock.

An earthquake happens when too much tension builds up from the plates moving. There is a focus point of the earthquake and then it spreads out in all directions. The depth tells us how far below the earth the earthquake originates at the focus point. The epicenter of an earthquake is the area on the earth's surface that is directly above the focus.  A small earthquake may last seconds and a larger one often will last minutes. After shocks are weaker earthquakes that happen after the main earthquake. After shocks may last for days or weeks.

 

Here are some free reading cards about earthquakes. For younger children, use the first three cards first.

Use the three period lesson to teach new terms. You can use this printout as three part or nomenclature cards.

For more about the earth's movement check out Plate Tectonics and Continental Drift.

References

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