Types of Seismic Waves - P, S and Surface Waves

Seismic waves are vibrations or disturbances that propagate through the Earth in response to the sudden release of energy from below the Earth's surface. This energy is released due to events such as earthquakes, volcanic eruptions or explosions. Discover more about what causes a volcano to erupt in our related article.

Seismic waves have several distinctive characteristics that we can use to differentiate the their different types. These are very important for seismological studies. Here are some of the most important characteristics of seismic waves:

• Propagation speed: seismic waves travel at different speeds through the Earth, depending on the type of wave and the material they pass through. P (primary) seismic waves are faster and can move through solids, liquids and gases. S (secondary) seismic waves are slower and can only move through solids. Surface waves also vary in speed depending on their type.
  
  
• Nature of Propagation: P waves are longitudinal waves, meaning they propagate by compressing and expanding the material in the direction of their movement. S waves are transverse waves and propagate by shaking the ground from side to side, perpendicular to the direction of propagation. Surface waves have a combined movement that can be both longitudinal and transverse.
  
  
• Ability to pass through materials: P waves can pass through solids, liquids, and gases, while S waves can only move through solids. This is due to the difference in the way these waves propagate and the stiffness of the materials.
  
  
• Amplitude and frequency: the different types of seismic waves vary in amplitude and frequency, which determines their energy and how they affect structures and soil. More energetic seismic waves can cause significant damage.
  
  
• Reflection and refraction: when seismic waves encounter a boundary between two types of materials with different properties, such as density or stiffness, they can be reflected or refracted. This allows seismologists to study the internal structure of the Earth, something which is made difficult due to our inability to access it directly.
  
  
• Interference and attenuation: seismic waves can interfere with each other and their amplitude decreases as they propagate through the material. Attenuation is the gradual reduction in the amplitude of waves as they travel through the Earth.
  
  
• Generation by seismic events: seismic waves are mainly generated by seismic events, such as earthquakes, volcanic eruptions and large explosions. Their detection and recording by seismographs allow scientists to study and understand these events and the internal structure of the Earth.

Seismic waves are very important to help us with our understanding of earthquakes, especially when it comes to prediction and protection of communities. Learn more with our article on how an earthquake occurs.

Seismic waves are divided into three main types based on their nature and the way they propagate through the Earth. They are:

P waves (primary or compression)

P seismic waves are the fastest and the first to arrive after an earthquake or other seismic event. They are longitudinal waves that propagate through the Earth, compressing and expanding the material in the direction of their movement. They can travel through solids, liquids and gases. They also have the ability to pass through the inner and outer core of the Earth. These waves are responsible for the initial shaking in an earthquake and are the least destructive compared to S waves and surface waves.

S waves (secondary or shear)

S seismic waves are slower than P waves, ocurring subsequent to them after a seismic event. They are transverse waves that propagate by shaking the ground from side to side, i.e. perpendicular to the direction of propagation. They can only move through solid materials, so they cannot pass through the Earth's liquid core. S waves are more destructive than P waves and can cause significant damage during an earthquake.

Surface waves

These waves propagate along the Earth's surface and are considered the most destructive type of seismic waves. Surface seismic waves are divided into two main types:

• Rayleigh waves: these waves have an elliptical movement that combines vertical and horizontal movements. They are responsible for the vertical and horizontal shaking felt during an earthquake. They can cause considerable damage.
  
  
• Love waves: Love waves have a purely horizontal movement and do not cause vertical movements in the ground. Although they are less destructive than Rayleigh waves, Love waves can still cause significant damage to structures.

These are the main types of seismic waves that can be observed when phenomena such as earthquakes occur. Their study is essential to understand how seismic energy propagates through the Earth, and the effects they can have on the surface.

Now that you know the different types of seismic waves, don't miss these articles on the biggest earthquakes in history and the difference between earthquakes and tremors.

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