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Seismic waves
Intermediate
P waves are longitudinal; S waves are transverse and slower.
Earthquakes generate P-waves (longitudinal, fast, through liquids too) and S-waves (transverse, slower, solids only), plus surface waves. The delay between them gives the distance to the epicentre; S-wave shadow showed the liquid core.
The P-S gap of 30 s ≈ 250 km.
Surface waves cause the most damage.
In more detail
Seismic waves are elastic waves that travel through the Earth. P waves are longitudinal and fast, while S waves are transverse and cannot pass through liquids.
Real-world uses
- Seismologists locate earthquakes from the arrival times of P and S waves.
- The absence of S waves through the core revealed its liquid nature.
- Seismologists locate earthquakes by the time difference between arrivals of P waves and slower S waves.
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Frequently asked questions
Why do P waves arrive first?
They travel faster than S waves, so they reach a seismometer first.
Do seismic waves reveal Earth's interior?
Yes, their speeds and paths show layers, including the liquid outer core.
Why do S waves not travel through liquids?
S waves are shear waves, and liquids cannot sustain shear stress, which is why the outer core blocks them.
Related topics in Waves & Sound
Dispersion · Waves in water · Tsunami and shallow water waves · Acoustics of rooms · Musical scales and intervals · Fourier analysis