The Science of Earthquakes: Understanding Weather Just for Kids!

Take your hands and slide them past each other with your palms inward. Notice that the motion is smooth. Now, close your hands into fists.

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Slide your knuckles past each other. Instead, your hands stop and start moving as you keep pushing them. What stops them from moving smoothly is friction. Friction is a natural force, like gravity. It tries to stop things from moving against one another. Friction is strongest when those things have rough surfaces. So, think about how powerful it is when whole, rocky plates are moving past each other! Not much happens when your knuckles shift. But, when plates do, everything around them is affected. Their sudden motion is so powerful it causes an earthquake.

As soon as two plates slide past each other suddenly , an earthquake is set in motion. Wherever they were stuck together becomes what we call the focus of the earthquake. From there, a lot of energy is let off. After they finally do, they release that energy in the form of seismic waves. Seismic waves sound like a complicated concept.

The Science of Earthquakes

But, they are just a form of energy that pushes things around. This causes quaking in the earth. Then, we start to feel them. This is the point above the focus on the surface of the Earth. Seismic waves from the focus reach the epicenter first but then spread out around it. This shakes the ground for a while, and that shaking is the part of the earthquake that we can feel. Not every earthquake is equally strong. Some barely move a picture frame while others cause a lot of damage.

To compare them, scientists have developed two related tools.

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A seismograph is a tool which measures seismic waves. It shows both the intensity of the waves and for how long they were sent out. While the edges of faults are stuck together, and the rest of the block is moving, the energy that would normally cause the blocks to slide past one another is being stored up. When the force of the moving blocks finally overcomes the friction of the jagged edges of the fault and it unsticks, all that stored up energy is released. The energy radiates outward from the fault in all directions in the form of seismic waves like ripples on a pond.

Earthquakes are recorded by instruments called seismographs. The recording they make is called a seismogram. When an earthquake causes the ground to shake, the base of the seismograph shakes too, but the hanging weight does not. Instead the spring or string that it is hanging from absorbs all the movement.

The difference in position between the shaking part of the seismograph and the motionless part is what is recorded. So how do they measure an earthquake? They use the seismogram recordings made on the seismographs at the surface of the earth to determine how large the earthquake was figure 5.

The length of the wiggle depends on the size of the fault, and the size of the wiggle depends on the amount of slip. The size of the earthquake is called its magnitude. There is one magnitude for each earthquake.

Scientists also talk about the intensity of shaking from an earthquake, and this varies depending on where you are during the earthquake. Seismograms come in handy for locating earthquakes too, and being able to see the P wave and the S wave is important. P waves are also faster than S waves, and this fact is what allows us to tell where an earthquake was.

Light travels faster than sound, so during a thunderstorm you will first see the lightning and then you will hear the thunder.

Frequently Asked Questions about Earthquakes (FAQ)

If you are close to the lightning, the thunder will boom right after the lightning, but if you are far away from the lightning, you can count several seconds before you hear the thunder. The further you are from the storm, the longer it will take between the lightning and the thunder.

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P waves are like the lightning, and S waves are like the thunder. The P waves travel faster and shake the ground where you are first.

Then the S waves follow and shake the ground also. If you are close to the earthquake, the P and S wave will come one right after the other, but if you are far away, there will be more time between the two. By looking at the amount of time between the P and S wave on a seismogram recorded on a seismograph, scientists can tell how far away the earthquake was from that location.

If they draw a circle on a map around the station where the radius of the circle is the determined distance to the earthquake, they know the earthquake lies somewhere on the circle. Scientists then use a method called triangulation to determine exactly where the earthquake was figure 6. It is called triangulation because a triangle has three sides, and it takes three seismographs to locate an earthquake.