What are seismic waves?

An earthquake produces three kinds of waves that travel through the Earth’s crust.

Check out this video explaining the seismic waves of the Christchurch February 2011 earthquake.

P waves

  • first waves to arrive
  • also called sound or compression waves
  • often heard rather than felt
  • travel at 4–8 km/sec (14,000–28,000 km/h) in the earth’s crust
  • do not generally cause a lot of damage except in the biggest earthquakes

S-waves

  • second waves to arrive
  • traveling at 2.5–4 km/sec (9000–14,000 km/h)
  • pack the bigger punch because they are bigger and move at right angles to the direction of travel
  • their side-to-side motion (like a snake wriggling) is what causes the most damage to structures
  • cannot travel through liquids because liquids have no shear strength

Surface waves

  • travel around the surface layers of the earth
  • are the slowest of the earthquake waves
  • can travel around the whole earth from large eathquakes many times before they become too small to record on seismographs.