Seismic waves

What causes an earthquake?

A sudden movement between tectonic plates in the earth’s crust.

What do earthquakes cause?

Seismic waves which carry energy away from the earthquake.

They pass through the earth and can be detected by seismometers in different countries.

What are the 3 main features of P waves?

• Longitudinal waves

• Can pass through both solids and liquids

• Travel faster than S waves

What are the 3 main features of S waves?

• Transverse waves

• Can only travel through solids

• Travel slower than P waves

When an S wave travels through the earth…

It doesn’t reach all the way around the surface.

The spots it doesn’t reach are called S wave shadow zones.

How did this help scientists learn about the earth?

Since they knew S waves could only travel through solids, they knew these shadow zones were caused by something liquid blocking their path, leading us to the discovery of the liquid outer core.

When a P wave travels through the earth…

It can be detected almost anywhere, yet there are some small gaps.

These spots are called P wave shadow zones.

These shadow zones occur because…

P waves travel faster in solid than in liquid.

Sometimes…

Faint P waves can be detected in the P wave shadow zones, which told scientists that the earth also contains a solid inner core.

In conclusion, seismic waves…

Help us learn about the structure of the inside of our earth, which would otherwise be impossible