Seismic Waves (HT only)
- Earthquakes produce two types of waves:
- P-waves (primary waves)
- S-waves (secondary waves)
- These waves pass through the Earth’s centre and can be detected at various points around the Earth using seismometers
- By carefully timing the arrival of the waves at each point, the location of the earthquake, along with its magnitude, can be pinpointed
P-Waves
- P-waves are longitudinal waves
- These waves can pass through solids and liquids
- P-waves are faster than S-waves
- They are very low frequency sound waves known as infrasound
- Infrasound is any sound below the frequency of human hearing (<20 Hz)
- The waves refract as they pass through the different layers of the Earth
- This refraction affects the regions in which waves can be detected, yielding important information about the nature and size of the Earth’s various layers
Low frequency sound waves (P-waves) produced by earthquakes, pass through the centre of the Earth, revealing useful information about its structure
S-Waves
- S-waves are a type of transverse wave
- Unlike P-waves, S-waves are unable to travel through liquids
- They pass through solids only
- S-waves are slower than P-waves
- This means that they are unable to travel through the Earth’s molten (liquid) outer core – providing important evidence about its state and size
Transverse S-Waves are unable to pass through the Earth’s liquid outer core
Examiner Tip
This topic covers the properties of longitudinal and transverse waves, how waves travel through different mediums, wave speed, and refraction, so its the perfect place to consolidate your conceptual understanding.
Students often struggle to remember the differences between S-waves and P-waves, so try writing out the following:
S-waves = Secondary waves (arrive second) slower speed, transverse, go through solids only
From this, you can remember that P-waves are primary waves (they arrive first), faster speed, they are longitudinal, they go through liquids as well as solids.