Plate Tectonic - Earthquakes (4)
Pre Lab 

  • Exploring how we can measure an earthquake
  • Comparing the Richter and Mercalli scales.
  • epicenter
  • focus
  • intensity
  • liquefaction
  • Modified Mercalli Scale
  • Richter Scale
  • seismic wave
  • worksheet

Students look at damage from seismic waves.

Building damaged in Japan


Earthquakes are caused when stress within the crust of the Earth builds up, causing an area of rock to "snap" along a fault. This breaking causes a release of energy. This energy is measured by how much "shaking" occurs. The shaking can vary in its intensity. Some earthquakes shake everything (high intensity), and others are not felt at all (low intensity). In these labs, we introduce two ways to measure this shaking: the Richter scale and the Modified Mercalli scale. The Richter scale is a mathematical measurement of the intensity of the ground shaking, as measured on a seismograph. It is actually a measurement of the size of the waves produced by the earthquake. The Modified Mercalli scale measures how people feel and react to the shaking.

Seismic waves radiate outward from the focus (point at which the earthquake starts). These waves cause damage in some areas and but not in others. Many factors effect damage. One of the most fundamental is distance: seismic energy is lost as waves travel through the Earth, so the further you are from the epicenter of an earthquake, the less shaking you will likely feel. Another important factor is the type of ground through which the waves travel. For instance, if the waves shake sand particles, the energy will tend to make the particles "settle." This may cause the Earth’s surface to sink; large movements can occur, damaging human structures. In contrast, if the wave past through hard, solid rock, no settling occurs, and the movement will be less. Basically, the more tightly bound a material is, the less it will settle in response to seismic waves.

  1. Explain the meaning of intensity, epicenter, and focus to the class. Explain that energy waves (seismic waves) are emitted from the focus (just like when you throw a pebble into the water and waves are emitted from the point of impact). Discuss how the strength of a substance effects how much it settles.
  2. Have the students complete the worksheet
  3. Answers:
  1. 2 and 3
  2. The seismic waves go through these homes. Homes #1 and #4 are not affected by the waves.
  3. House #4, because the intensity of an earthquake is felt less, the farther it is from the epicenter.
  4. B, because when the ground shakes it will not collapse.

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