S Waves

In the field of seismology, S waves refer to a type of elastic wave that happens to be one of the two main types of elastic body waves. These waves are also known as secondary waves or shear waves or elastic S waves. Furthermore, their name secondary wave is because they are the second type of wave whose detection took place by a seismograph, following the P wave.

Introduction to S Waves

S waves are a type of transverse wave. What this means is that the oscillations of an S wave’s particles are perpendicular to the wave propagation’s direction.

The main restoring force is because of the shear stress. Therefore, the propagation of S waves cannot take place in liquids with very low or zero viscosity. However, their propagation may take place in liquids with high viscosity.

s waves

                                                                                                                        S Waves

Relation Between S Waves and P waves

In contrast to the P waves, S waves cannot travel through the Earth’s molten outer core, and this leads to the creation of a shadow zone for S waves opposite to their origin. Their propagation can still take place through the solid inner core.

When a P wave strikes, at an oblique angle, the boundary of molten and solid cores at an oblique angle, the formation and propagation of S waves will take place in the solid medium. When these waves hit the boundary again at an oblique angle, they will cause the creation of P waves whose propagation takes place through the liquid medium.

Earthquake Waves

When an earthquake occurs, a release of waves of energy takes place. Such waves are known as Seismic waves.

It is like the ripples whose creation takes place in water if someone throws a stone in it. Seismic waves are like those ripples whose travelling can take place through the Earth’s inside, as well as on the Earth’s surface.

On the basis of the medium they travel in, the classification of earthquake waves can be done under two categories:

  • Body waves
  • Surface waves

Body waves are those waves whose travelling can take place through the earth. Furthermore, their origination is at the earthquake’s epicentre and they travel at amazing speeds through the earth. The two types of body waves are the P wave and S wave.

Surface waves are the ones that travel on the Earth’s surface. Moreover, they are responsible for the destruction caused by earthquakes.

Method of Predicting S Waves Velocity

Prediction of shear-wave velocity is crucial in seismic modelling, amplitude analysis with offset, and various other exploration applications. Furthermore, one can predict S wave velocity from the P wave velocity based on the moduli of dry rock. Furthermore, the prediction of elastic velocities of water-saturated sediments at low frequencies can take place from the moduli of dry rock by making use of Gassmann’s equation.

As such,  if experts can estimate the moduli of dry rock from P wave velocities, then they can easily predict S wave velocities from the moduli. Moreover, dry rock bulk modulus may have a relation to the shear modulus through compaction constant. Also, the numerical results give us the indication that the predicted S wave velocities for consolidated and unconsolidated sediments agree well with measured velocities if differential pressure turns out to be greater than approximately 5 MPa.

A significant advantage of this method is that there is no requirement for adjustable parameters like the pore-aspect ratios that are needed in some other methods. Moreover, the prediction of S wave velocity is only on the measured P wave velocity and porosity.

FAQ on S Waves

Question 1: What are the main differences between the S waves and P waves?

Answer 1: The main differences between S waves and P waves are:

  • P waves are the first wave to hit the earth’s surface while the arrival of S waves is after them.
  • P waves have a speed range of 1.5-13 km/s while S waves happen to be 1.7 times slower than them.
  • While S waves are able to travel through solids only, P waves can travel through all three states of matter- solid, liquid, and gas.
  • S waves travel in a transversal direction while the P waves, in contrast, travel in a linear direction.

Question 2: What are the S waves characteristics?

Answer 2: S waves are a type of transverse wave that can travel through solid only. Furthermore, they are one of the two main types of elastic body waves. Also, the travelling speed of this wave is 1.7 times slower than P waves.

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