How Do We Know about Layers Deep within Earth?
ES0402  Seeing with Seismology

When an earthquake occurs, seismic waves travel through the planet. Every earthquake generates two types of waves—primary, or P waves, and secondary, or S waves. A worldwide network of seismometers, instruments that track earthquakes, records the arrival of P and S waves from all over the globe. Observations and analysis of the waves have led geologists to infer the internal structure of Earth.

This simulation shows P and S waves moving along Earth’s surface away from an earthquake.

  !   Click the image to see the animation. Observe the types of materials through which each wave passes.

Tom Grace,TERC

3.What types of material do P waves pass through?

4. What types of material do S waves pass through?

  !   Click and drag the slider back and forth to compare the speed of both waves. Which type of wave moves faster?

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