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Information places on earthquakes and plate tectonics :

NASA-continental drift

San Andreas Fault tectonics

  science kids

An earthquake is a sudden release of stored energy. Earthquakes occur when slow but powerful tectonic forces cause stress to build up in the Earth’s crust. When the stresses get large enough, slippage is triggered along fractures in the rock known as faults. The sudden slipping motion along a fault causes vibrations known as seismic waves to form and travel away from the zone of slippage. Several meters of slip along a large fault causes a major earthquake; a few centimeters of slip on a small fault (perhaps the size of a soccer field) would cause a small earthquake. Larger earthquakes cause stronger seismic waves.

Seismic waves that travel through the rocks of the Earth’s crust are similar to the ripples that spread across the surface of a pond after a rock splashes into the still water. However, seismic waves travel much faster than water waves. The rumbling noises or shaking motion that you might experience during an earthquake are caused by seismic waves passing through the rocks beneath our feet.

Seismographs are sensitive instruments that record the vibrations of passing seismic waves. Using the recordings from a group of seismograph stations (a seismic network), a seismologist can determine the location (epicenter), depth (focus), and size magnitude) of an earthquake. The size of an earthquake is rated on a magnitude scale. The most popular magnitude scale is the Richter scale but the Moment magnitude scale is more accurate. On either scale, an increase of one magnitude unit indicates a ten-fold increase in seismic shaking.


Magnitude 1–2

  • 2.0=13 lbs TNT

Only detected by instruments such as seismographs (over half a million per year).

Magnitude 5–6

  • 6.0=6,270 tons TNT
Felt strongly. There is some building damage (hundreds per year).
Detected by instruments and felt a little by people (hundreds of thousands per year). Severe. Buildings and chimneys collapse (20 to 200 per year).
Felt slightly. Bells might ring, lights might move (tens of thousands per year). Magnitude 7–8
  • 8.0=6,270,000 tons TNT
Severe. Buildings collapse and cracks form in the ground (10 to 20 per year).
Felt strongly. Some glass and building damage occurs (thousands per year).

Magnitude 8–9

  • 9.0=1999,999,000 tons TNT
Mass destruction. Buildings, bridges, and roads collapse (one per year at magnitude 8, one per decade at 9 magnitude).

What you'll need:

  • large marshmallows
  • peppermint candy
  • toothpick
  • small saucepan
  • cup of chocolate chips
  • wax paper

Cut a small slit in the marshmallow and stick the peppermint in the middle. Put the marshmallow on the toothpick. Melt the chips in a saucepan over a very low heat, stirring them so they don't burn. Dip the marshmallow in the melted chips completely coating it. Place on wax paper to cool.

Layer by Layer

The outer layer (chocolate) is the earth's crust. Just as with the real earth, it was formed from hot melted material that cooled down and hardened.

The soft, gooey middle layer (marshmallow) is the earth's mantle. It's about 1,800 miles thick, or about the distance you'd go if you drove halfway across the U.S. It's made of magma.

When you strike the candy in the middle, you've hit the center of the earth, called the core. Scientists belieive that the earth's core is a solid kernel of metal surrounded by a layer of liquid metal. The core is just a bit thicker than the mantle and about 9,000°F— almost as hot as the surface of the sun.

You've just made a mini earth!
And to take a quick trip to the center of your earth, just take a bite— in the name of science of course.

A crack in the earth's crust is called a fault. The large crack where two huge earth plates move against each other is a fault line. Fault lines are where the action happens.

What you'll need:

  • Graham crackers
  • Waxed paper spread with a thick layer of frosting or peanut butter.
  • Milk

moving platesPut two graham crackers side by side, and slide one up away from you and the other one down toward you.

When plates move past each other like this, things don't exactly go smoothly. In fact, the plates usually get stuck on each other and then give a lurch and move on, sending waves of vibrations through the earth's interior (much like the circular waves that ripple out when you drop a pebble in the water). These vibrations are so powerful the we have a special name for them— earthquake!

crumbled togetherPut two graham crackers side by side on the wax paper (wet the edge of one graham cracker in milk first), and slowly push them together.

The ridge of pushed -up cracker is just like many mountin ranges around the earth that were formed as two plates slowly crumbled together over millions of years. The Himalayas ( the mountian range that includes Mount Everest) were formed when India crashed intio Asia

separating platesPut two graham crackers very close to each other on the wax paper and slowly push them together.

You've made a rift, or big crack in the ocean floor. As the plates separate, magma oozes up from below and makes new ocean floor or creates underwater mountain ranges.

melting platesPush two crackers toward each other, make one slide underneath the other.

When this happens on earth, watch out! The bottom plate starts to melt from the intense heat and pressure. It becomes new magma that floats up between two plates, building up and up over many years until it finally causes a volcano blast! That plate action caused Mt. St. Helens in Washington State to blow its top!

These two delicious and fun projects and many more can be found in
, a Williamson Publishing book by Cindy Blombaum

sanandreasWhose fault is this?

What if you went outside after an earthquake and found the rasberries your family planted in the front yard were growing in front of your next door neighbor's house (and in your yard were the roses from the next house)? This is what happened in San Francisco along one of the most famous fault lines in the world— the San Andreas Fault in California, a 600 -mile boundary where the American and Pacific Plates meet. In 1906, there was an earthquake along this fault line and the earth moved about 20 feet in less than a minute! Wonder who got to eat the ripe berries?

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