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Seismic Waves (Earthquake Waves)

Seismic waves are waves in the earth caused by earthquakes, volcanic activity, magma movement, and landslides. They can be very large or so small that you and I can’t feel it. They are recorded with something called a seismograph. Let’s learn about it!
Seismograph reading.

An example of seismic activity.

What are the different types of Seismic Waves?

There are three main types of waves. 
  1. Primary Waves (P Waves) – These waves are recorded by the seismograph first. They are longitudinal, which means that they move from side to side. They shake the Earth in the direction that they move. This type of wave can travel through liquid and to the Earth’s core.
  2. Secondary Waves (S Waves) – These waves are recorded by the seismograph second. These waves shake the Earth perpendicular to the direction that they move in. They move up and down. Secondary waves cannot travel through Earth’s liquid outer core.
  3. Surface Waves – These waves are recorded by the Seismograph last. These waves can only move through the surface of the Earth, unlike P and S waves that can move through the inside.
Needle on a seismograph working.

An example of a seismograph in action.

How Fast can Seismic Waves Travel?

Seismic Waves are pretty darn fast! When traveling through the air, P Waves can move at about 330 m/s*. In water, they can move at about 1450 m/s. When they travel through granite, they can move at 5000 m/s! That’s fast! 
Because S waves cannot travel through liquids, they move at about 60% of the speed that P waves do through any material. With that said, even though P waves move faster than S waves, they are still very powerful.
(*Meters per second)

What is a Seismograph? How does it work?

A Seismograph detects and measures the movement of the Earth. A weight is suspended in a way that lets it detect when the ground moves, and it records the movement for us. Seismologists will use the data recorded by the Seismograph to detect earthquakes. It can also detect volcanic activity, and other similar things.
Seismograph instrument recording ground motion during earthquake.

An example of a simple seismograph.

Other Great Resources:

How a Seismograph Works – KidsKnowIt – 

Seismology – SimpleWikipedia – https://simple.wikipedia.org/wiki/Seismology
Written by: Hannah Bertoch.