Seismic Waves

Seismic waves are produced in the Earth’s crust when large-scale events take place. For example, earthquakes and volcanic eruptions. These waves then spread in all directions through the layers of Earth, often causing damage to structures on the surface of the Earth.

There are two types of seismic waves:

  • P-waves (primary waves) – longitudinal waves, which travel through both solids and liquids – Travelling at different speeds through each medium and are much faster than s-waves
  • S-waves (secondary waves) – transverse waves, which only travel through solids – This means that they cannot travel through Earth’s liquid outer core

Both p-waves and s-waves are refracted at the boundaries between the different layers. This is because the layers have different densities. Keep in mind, that refraction is when waves change direction as they pass from one medium to another.

By studying how seismic waves travel, scientists can map out the internal structure of the Earth. This helps us understand what Earth is made up of, as these features are not directly observable.

Seismologists use seismometers to detect the waves, and by observing these readings, it is possible to measure the depth of the Earth’s layers. This is because they can calculate how long it takes the seismic waves to travel from the earthquake site to different areas on Earth.

  • S-waves are not detected on the opposite side of the earthquake site. This shows that the mantle is solid, but the outer core must be liquid.
  • There are two shadow zones where no P-waves are detected. This is due to the refraction between layers. The size and positions of these shadow zones indicate that the inner core is solid.