Plate Tectonic - Earthquakes (2)
Post Lab 

  • Exploring how deep you can drill into the Earth.
  • Determining where earthquakes occurs.
  • core
  • crust
  • drill
  • earthquake
  • paper plate
  • crayons

Students make a paper plate model of the Earth.

The aftermath of an earthquake in Turkey


Scientists have determined that the center of the earth is 6371 km below the surface. But how has this been determined? Many people might answer that question by saying scientists can drill into the Earth with machines. However, the drilling rigs that scientists use can only drill about 20 km in the Earth which is not very deep! In other words, we can only drill into upper part of the crust of the earth. Extremely high temperatures and pressures within the Earth make drilling into it very difficult.

Earthquakes are caused by the sudden movement and fracturing of rock masses along preexisting faults. A fault is a broken surface within the Earth’s crust. The point on the fault at which the displacement begins is called the focus of the earthquake. The point on the surface of the earth directly above the focus is the epicenter. Your students need to understand that an earthquake happens in rocks that have been stressed. This stress is stored until the strength of the rock is exceeded. The actual break (the earthquake) then releases the energy. This energy travels in the form of seismic waves.

The seismic waves generated by an earthquake can be recorded and measured on a seismograph. The interpretation of the waves provides seismologists with a way of "seeing" into the inside of the Earth. The waves produced by earthquakes travel through the Earth and bounce off different features of the Earth's interior. The patterns they form after bouncing off these features can be used to create images of the interior.

Earthquakes generate many different types of seismic waves. Two major types are P (push/pull; compressional, or primary) and S (shear or secondary). There are some basic rules that you need to understand. P-waves are faster than S-waves; S-waves cannot travel through liquid; P-waves can travel through liquids and solids, and both types of waves go faster through denser rock and slower through liquids. These basic facts (plus many more) help geologists and seismologists to interpret the inner structure of the Earth. For example, when S-waves are not received by a seismometer, it suggests that a liquid layer is present inside the Earth which we call the outer core.

  1. The students have learned that most earthquakes occur in the outer most portion of the Earth. Draw a picture of the Earth on the board as shown to the right. A = 1200 km (inner core); 2200 km (outer core); C= 2900 km (mantle); D = 7-100 km (crust). Ask students how far they think it is to the center of the earth from the surface. Have some volunteers come to the board and place an X at the depth to which they think we can drill.
  2. Ask the students how they think scientists know what is inside the Earth. Explain that scientists can study the patterns of seismic waves released by earthquakes to determine the Earth’s internal layers. You do not have to give much detail, just dispel the notion that we can drill to the center of the Earth
  3. You may want to have students make a paper plate model of the inside of the Earth. Instruct students to label layers as in the diagram. Label depths as follows: A = 1200 km (inner core); 2200 km (outer core); C= 2900 km (mantle); D = 71 km (crust).

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