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What are Seismic Waves

An Outline of What Exactly Seismic Waves and its Types Are

Wanting to know what are seismic waves? Also, what is their source of occurrence and how many types are included under this same subject? Look below for the answers to these questions.
Fatima Rangwala
Last Updated: Dec 09, 2017
The energy waves that radiate when an earthquake or a tsunami bursts out on Earth are called seismic waves. As a matter of fact, any natural calamity which happens on Earth, radiates certain amount of waves or shock waves when the crust of the Earth suddenly shifts or breaks apart. Such types of shock waves that vibrate and travel under the surface or through the surface of the Earth are termed as seismic waves. The study of such waves by the process of observing, monitoring, analyzing and measuring earthquake activities using specific instruments is called seismology.
Seismic Waves: An Overview
The energy waves that are generated on any sudden explosion or breaking of rocky or encrusted regions within the surface of the Earth are named as seismic waves. They are the actual energy waves, a.k.a., shock waves that travel down through the core of the Earth and generate vibrations on the entire surface of the planet. Scientifically, these waves are known to be caused by too many reasons and not because of just one reason in specific.
The waves can occur due to:
  • Strong winds on the surface
  • Iterative ocean waves
  • Natural calamities like tsunamis, earthquakes, volcanoes, hurricanes, etc.

In this manner, if there is any movement with the Earth's tectonic plates, some amount of natural energy is bound to radiate off the surface of the Earth and hit the home ground in the form of waves. That is what explains the existence of these waves.
For your basic knowledge, the people who study the nature of a seismic wave are called seismologists, the field is known as seismology and the process they expend to measure and analyze the activity of the Earth's tectonic plates is measured by a seismograph. Seismology, as a field in the subject of geology, is a very interesting branch. One can easily study the occurrence of seismic waves, shock waves and energy waves that occur due to natural calamities, right in this field.
Types of Seismic Waves
Speaking of the types of waves, as such, there are several types of seismic waves that occur in different ways and in different movements. But the two main are the Body waves and the Surface waves. There are other forms of wave propagation as well, but their importance is minor and are mainly used in studying helioseismology and asteroseismology. For now, let's elaborate on each of these types and see their individual properties as well.
Body Waves
Body waves are known to travel through the interiors of the Earth. Just before the surface waves are emitted, due to the effect of a volcano or an earthquake, body waves arrive traveling through the core (interiors) of the Earth. Body waves refract, curve and bend at certain paths depending on the objects they pass through. The waves usually follow curved path patterns only because the Earth's interior has a varying composition and density. Moving further, body waves are divided into two main categories: Primary waves (P) and Secondary waves (S).
Primary Waves: Primary waves are the kind of seismic waves that travel at a very high velocity under the surface of the Earth and are known to be the first-sighted waves at the time of any natural calamity. The earth's surface is constantly alternating, i.e., it's compressing and decompressing in the direction of the propagation of waves, time and again.
Thus, the P-waves travel through the action of expansion and compression at a speed twice as fast as secondary waves and through any material, be it solid or liquid. P-waves are also called compressional waves or pressure waves that are longitudinal in property. The best example to consider would be, a dog beginning to bark hysterically long before an earthquake is hit. That's because seismic waves travel faster at 5000 m/s underground before you experience the rattling. Dogs are able to catch such a high frequency.
Secondary Waves: Secondary waves or the S-waves are the energy waves that we experience after the earthquake has been hit. These waves are comparatively slower than the P-waves and they travel strictly through objects which are solid only. S-waves are also referred to as shear waves, which are typically transverse in nature. S-waves follow P-waves at a very close distance during an earthquake and the displacement is typically perpendicular, alternating to one side and then the other, depending upon the direction of the propagation of the seismic waves.
With this explanation, now, let's take a peep at the second type, the surface waves.
Surface Waves
As compared to body waves, surface waves travel at a very low frequency but cause more destruction, amplitude and resonance to the objects in the environment, here, on the surface. They are more like ocean waves or water waves, which travel along the surface of the Earth. Speaking of their types, surface waves have two types: Rayleigh waves and Love waves.
Rayleigh Waves: Rayleigh waves are named after Lord Rayleigh, a.k.a., John William Strutt, a mathematician who predicted the emergence of Rayleigh waves back in 1885. Rayleigh waves are ground-rolling waves moving along the surface of the Earth, just like any other wave in the ocean or in the sea would do. These waves are known to carry a lot of impact at the time of an earthquake. All the rattling and shaking we experience during the quake, is due to Rayleigh waves.
Love Waves: Similar to Rayleigh waves, Love waves are named after a British mathematician, A.E.H. Love who had thoroughly worked on a mathematical model back in 1911, just to study the properties of Love waves. The waves move from surface-to-surface and enclose the surface of the Earth's crust. L-waves travel at a speed - 90% faster than the S-waves velocity, with a very high amplitude.
Studying about several types of seismic waves articulates us with a lot of information about the general nature of the Earth's structure. These waves are most useful for mapping, i.e., with the use of seismographs, seismologists can actually tell us the difference in the arrival period between the P-waves and the S-waves, so that the distance to the source of a natural calamity can be determined instantly.