Earthquake Shock Waves

Types of shock waves earthquakes

As we've previously discussed, earthquakes generate more than one kind of shock wave. There are four different types of shock waves, all with different properties.

P-waves

P-waves are the first of the shock waves to occur after the earthquake, and one of the two main shock waves to occur overall. This wave is also known as a compressional wave, and it is also longitudinal. This means that the wave creates areas of compression and dilation that travel along the surface of the earth, disrupting anything on this ground as it travels across it. As this is the first type of shock wave to occur in an earthquake, it is the first detectable shock wave by technology.

Fig. 3: A P-wave in action. Compressions and rare factions can be seen.

S-waves

S-waves are the second type of shock wave to occur after the earthquake, and also the second of the two main shock waves that occur overall. These are different to P-waves in that they are transverse waves instead of longitudinal waves. This means these are the waves that propagate perpendicular to the direction of oscillation, therefore the oscillation is perpendicular to a P-wave. Because these waves are transverse, S-waves cannot travel through liquid, this includes magma and molten rock underneath the Earth's surface. These shock waves can also be called shear waves.

Fig. 4: An S-wave in action.

Rayleigh-waves

Rayleigh-waves might be a type of shock wave to occur in an earthquake that you haven't heard of before. Rayleigh-waves travel across the Earth's surface in an elliptical pattern. As a result of this, Rayleigh-waves have a horizontal and a vertical component to their shock waves.

Fig. 5: A Raleigh-wave in action.

Love-waves

Love-waves are also a type of shock wave to occur in an earthquake that you may not be familiar with. Love waves are also a surface wave, meaning they travel along the surface of the Earth. This makes them quite similar to Rayleigh-waves, however, the key difference is that Love Waves travel as a transverse wave as opposed to the more elliptical motion of the Rayleigh-waves.

Fig. 6: A Love-wave in action.

Earthquake shock waves speed

As we know, earthquakes generate more than one kind of shock wave. As a result, these different kinds of shock waves all move at different speeds.

P-Waves have a range of velocities, from \(629\,\,\mathrm{m}/s\) to \(2599\,\,\mathrm{m/s}\). S-waves are slower than P-waves, ranging from about \(288\,\,\mathrm{m/s}\) to \(1200\,\,\mathrm{m/s}\). We can think of Rayleigh-waves as like waves in the water, making them travel at a few kilometres a second. Similarly, Love-waves will travel between \(2-6\,\,\mathrm{km}{s}\).

The most powerful shock waves from an earthquake

Before we're able to cover the most powerful shock waves, and therefore the most powerful and destructive earthquakes to have ever occurred, we first need to learn about how the power of earthquakes is measured. The technology we use to record the intensity of earthquakes are called seismographs.

Fig. 7: A seismometer inside a seismograph. Look at how the whole thing is bolted down for it to work properly!

Fig. 8: An example of how an earthquake looks on the Richter scale.

So now that we know how earthquakes are measured, what units do we measure them with? Earthquake shock waves are measured using the Richter scale, a scale used to measure the size (also known as magnitude) of an earthquake, therefore how powerful the shock wave of an earthquake is. The measurement of an earthquakes shock waves is determined using the amplitude of the largest shock wave the seismograph registers. The amplitude of a wave is the height that it reaches, the higher the height meaning the more powerful the wave.

Now that we know how earthquake shock waves are measured, and what scale they are measured on, let's look at the most powerful recorded earthquake in history. The most powerful earthquake to ever occur happened near Valdivia in Chile, in 1960. This earthquake registered on the Richter scale as a 9.5 magnitude, also causing an enormous tsunami to occur that travelled at nearly 200 miles per hour.