Three Types of Seismeic Waves

By Luke Mulhern

What actually is a seismic wave?

A seismic wave is usually caused by movements in the Earth's tectonic plates. It can also be caused by volcanoes, landslides, and explosions. They produce energy that temporarily shakes the earth and causes eathquakes. The three main seismic waves are Primary or P waves, Secondary or S waves, and Surface waves.

P (Primary) waves

Primary waves can be also known as Compressional waves or Longitudinal waves or even seismic body waves . These waves travel at 1.5-8 km/sec (which is fastest out of all three) in the earths crust as they shake the ground in the direction that they are putting force towards. Usually the spot that the waves move in is the Earth's core. These waves usually cause very little damage. Something else that is interesting is that the waves can move through a solid rock as well as a liquid. Lastly, these waves can cause houses to move up and down.

S (Secondary) waves

The Secondary waves can also be known as Shear waves. They always travel directly following a primary wave. These waves are second to arrive at the seismic station which is right after the Primary waves. They move 1.7 times slower than the Primary wave and the damage they cause is that the waves move the surface of the earth side to side since that is where the waves are moving and putting their force towards. These waves are much more dangerous than Primary waves since they have more amplitude and make a vertical and horizontal movement in the grounds surface. One thing that makes them different than Primary waves is that they do not travel through liquids like water, molten rock, or Earth's outer core.

Surface waves

Something that makes these waves different than Primary and Secondary waves is they do not penetrate the interior of the earth's surface. Another way to say this is they do not go inside the earth. The waves arrive last at the seismic station and can cause a lot of damage since while it drifts along the surface it can lift and drop the ground as it passes. They usually happen less than any wave are the easiest to distinguish on the seismograph as a result. The damage is mostly reduced in a deeper kind of earthquakes. There are two different categories to these waves, Love and Rayleigh. A Love wave has side to side movement which can cause the ground to twist from side to side. A Rayleigh waves move rolling up and down and are mostly generated by deep earthquakes.
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