Earthquakes will rock your world moving plates continue

What is an earthquake?

An earthquake is what happens when two blocks of the earth suddenly slip past one another. The surface where they slip is called the fault or fault plane.

The location below the earth’s surface where the earthquake starts is called the focus and the location directly above it on the surface of the earth is called the epicenter.

Large blocks of rock slipped past each other.

4. What causes earthquakes and where do they happen?

Anywhere there are moving plates!

REVIEW: We have researched the layers of the Earth recently: earth has four major layers: the inner core, outer core, mantle and crust. The crust and the top of the mantle make up a thin skin on the surface of our planet. But this skin is not all in one piece – it is made up of many pieces like a puzzle covering the surface of the earth. Not only that, but these puzzle pieces keep slowly moving around, sliding past one another and bumping into each other. We call these puzzle pieces tectonic plates, and the edges of the plates are called the plate boundaries.


The plate boundaries are made up of many faults, and most of the earthquakes around the world occur on these faults.

Edges of the plates are rough, they get stuck while the rest of the plate keeps moving.

When the plate has moved far enough, the edges unstick on one of the faults and there is an earthquake.



Some 80 percent of all the planet's earthquakes occur along the rim of the Pacific Ocean, called the "Ring of Fire" because of the preponderance of volcanic activity there as well. Most earthquakes occur at fault zones, where tectonic plates—giant rock slabs that make up the Earth's upper layer—collide or slide against each other. These impacts are usually gradual and unnoticeable on the surface; however, immense stress can build up between plates. When this stress is released quickly, it sends massive vibrations, called seismic waves, often hundreds of miles through the rock and up to the surface. Other quakes can occur far from faults zones when plates are stretched or squeezed.

Why is this sign here? Where are "you" coming from?


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. Potential energy! 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.


  • energy radiates outward from the fault in all directions in the form of seismic waves like ripples on a pond.
  • Seismic waves shake the earth as they move through it, and when the waves reach the earth’s surface, they shake the ground and anything on it, like our houses and us!

8. How are earthquakes recorded?

8. Earthquakes are recorded by instruments called seismographs.

  1. The recording they make is called a seismogram.
  2. The seismograph has a base that sets firmly in the ground, and a heavy weight that hangs free.
  3. When an earthquake causes the ground to shake, the base of the seismograph shakes too, but the hanging weight does not.
  4. 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.

9. How do scientists measure the size of earthquakes?

The size of an earthquake depends on the size of the fault and the amount of slip on the fault, but that’s not something scientists can simply measure with a measuring tape since faults are many kilometers deep beneath the earth’s surface.

  1. 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 .
  2. A short wiggly line that doesn’t wiggle very much means a small earthquake, and a long wiggly line that wiggles a lot means a large earthquake.
  3. 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.

10. How can scientists tell where the earthquake happened?

Seismograms come in handy for locating earthquakes too, and being able to see the P wave and the S wave is important. You learned how P & S waves each shake the ground in different ways as they travel through it.

  • The first to arrive at the seismograph: Primary Waves or P waves are also faster than S waves, and this fact is what allows us to tell where an earthquake was. To understand how this works, let’s compare P and S waves to lightning and thunder. Light travels faster than sound, so during a thunderstorm you will first see the lightning and then you will hear the thunder. 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.

P waves are like the lightning, and S waves are like the thunder.

  • P waves travel faster and shake the ground where you are first.
  • 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. However, they can’t tell in what direction from the seismograph the earthquake was, only how far away it was. 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. But where?

Know this Vocabulary for Earthquakes: Faults, Seismic waves, S Waves, P waves, Surface Waves, Focus, Epicenter, Tension, Shearing, Compression, Reverse fault, Normal Fault , Strike-slip Fault, Hanging Wall, Footwall

credits to:

Created By
Laurie Haddock


Created with images by gideon_wright - "Trashed Earth" • Ninara - "Y1A0212 Naivasha Kenya" • Ninara - "_Y1A0186 Hell's Gate, Kenya" • eleephotography - "Capitol Reef National Park-2" • Ninara - "Y1A0252 Naivasha, Kenya" • James St. John - "End-Pleistocene large pothole in tholeiitic basalt (Clam Falls Volcanics, Mesoproterozoic, ~1.1 Ga; Interstate State Park, Taylors Falls, Minnesota, USA) 7" • goingslo - "San Andreas Fault - California" • Hitchster - "faulted" • naotakem - "San Andreas Fault: Midpeninsula - South Bay" • dsearls - "2013_06_25-26_syd-akl-lax-iad-ewr_100" • dsearls - "2015_06_19_ewr-lax_393" • dsearls - "2013_06_25-26_syd-akl-lax-iad-ewr_078" • Michael R Perry - "San Andreas Fault (geotagged)" • naotakem - "San Andreas Fault: San Francisco - Peninsula" • basykes - "P1190162" • brettneilson - "Shaker"

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