S-Waves: Definition & Examples

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  • 0:00 Secondary Waves Defined
  • 1:14 Velocity
  • 1:38 Seismic Shadow Zone
  • 2:21 Lesson Summary
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Lesson Transcript
Instructor: Jeff Fennell

Jeff has a master's in engineering and has taught Earth science both domestically and internationally.

S-waves are seismic waves produced by the energy released during an earthquake. S-waves can cause intense damage to structures and are important in determining the location of the epicenter. This lesson will cover the facts about S-waves.

Secondary Waves Defined

Secondary waves, or S-waves, are seismic waves produced by an earthquake. As one side of a fault slips past the other, the pressure that had been stored is released and travels radially away from the focus of the earthquake.

S-waves are lateral waves that move side to side as a sine wave perpendicular to the direction of the wave. They are the second seismic wave to be felt or recorded during an earthquake, after the conveniently named primary wave. If you have ever experienced an earthquake, the intensity of the earthquake grows after the first initial jolt. When compared to other seismic waves, S-waves are the most destructive of all seismic waves.

S-waves are more destructive than P-waves. The lateral movement of the wave produces a rolling effect along the surface that can cause damage to all types of structures.

During the 1989 Loma Prieta earthquake in San Francisco, S-wave were especially destructive. Parts of San Francisco were built on wet, sandy soils. When the S-wave passed through these soils, a process called liquefaction occurred that shook the soils so much it essentially acted as a liquid.


S-waves travel slower than the primary waves. We can use the time difference between the arrival of the P-wave and S-wave to determine how far the epicenter is located from the location recording.

The farther away a location is from the epicenter of an earthquake, the greater the arrival time difference is between the of the P & S waves.

  • One location can determine its distance to an epicenter (A)
  • Two locations can narrow the epicenter down to two places (A & B)
  • Three locations can pinpoint the epicenter of an earthquake (A, B, & C)


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