AQA GCSE Seismic Waves - Science Worksheets

AQA GCSE Seismic Waves(Physics)

Seismic Waves.

The Earth’s surface is made up of tectonic plates. Sometimes these plates will wedge and suddenly move causing a jolt, this creates an Earthquake.

When the Earthquake occurs, seismic waves will travel through the structure of Earth.

There are different types of Seismic waves

1. P waves (primary waves)

2. S waves (secondary waves)

P waves(Primary Waves)

P waves are the fastest seismic waves, they are called primary waves because they are detected first by a seisometer.

P waves are longitudinal waves, this means that they vibrate along the direction in which they transfer energy.

P waves are able to travel through both solids and liquids.

Medium	Speed of p waves (m/s)
Water	1500
Rock	4000

S waves (Secondary Waves)

S waves travel slower than P waves, so they take longer to reach the seisometer, so they are detected later.

S waves are a transverse wave, this means that they vibrate at 90 degrees to the direction in which they transfer energy.

S waves can only travel through solids, they cannot travel through liquids.

Seisometer

A seisometer is a device that is used to detect an Earthquake. It produces a seismogram to show the P waves and the S waves, see below.

Investigating the Structure of the Earth with seismic waves.

Seismic waves, such as P waves and S waves provide us with information on the structure of the Earth.

We can only drill down about 12km into the crust of the Earth, so seismic waves are really useful to provide us with information on the Earth’s structure. The Crust can be 80km thick in some parts, so 12km is not that deep at all.

Below are images of P and S waves travelling through the Earth’s structure. They provide evidence about the structure of the Earth.

1.Evidence that there the outer core is liquid is provided by P waves being refracted (change direction) at the boundary between the mantle and the outer core, this direction change happens twice, once when entering and once when leaving the outer core. This leads to the formation of a P-wave shadow zone.

The other evidence for outer core being liquid is that S waves will NOT travel through the outer core, this creates a large S wave shadow zone.

2. Evidence that the inner core is a solid, is provided by the existence of VERY weak P waves within the P wave shadow zone. These are caused by the solid inner core refracting P waves into the Shadow zone. The waves are so weak, they have not been shown on the diagram above!

3. Evidence of a boundary between crust and mantle is proved by the speed of P waves changing at a depth of 50-80km within the Earth’s structure

Using Seismic Waves to determine the size of the core

The P-wave shadow zone helps determine core size.

P-waves do travel through the core but are refracted (bent) at the boundary between the mantle and the core.

This creates a P-wave shadow zone, where no direct P-waves are detected.

The way P-waves are refracted helps scientists estimate the size of the core.

By analyzing the arrival times and angles of seismic waves at different locations, geophysicists have been able to estimate the radius of the entire core (~3,485 km).

Practice Question

1.State the name of the two types of Seismic Waves.

2. State 3 characteristics of P waves

3. State 3 characteristics of S waves

4. What is the role of a seisometer?

5. During an earthquake would a person within the area experience a P wave or S wave first

6. Describe the evidence for the outer core being liquid

7. Describe the evidence that the inner core is solid