As a geophysicist with a focus on seismology, I can provide a detailed explanation regarding the propagation of S-waves through different materials, particularly liquids.

Seismic waves are categorized into two primary types: body waves and surface waves. Body waves consist of P-waves (primary or compressional waves) and S-waves (secondary or shear waves). P-waves are longitudinal waves that travel faster and can move through solids, liquids, and gases, causing particles to vibrate in the direction of the wave's propagation. S-waves, on the other hand, are transverse waves that travel slower and cause particles to vibrate perpendicular to the direction of the wave's propagation.

The ability of S-waves to propagate through a medium is dependent on the medium's rigidity and shear strength.
Solids possess both the necessary rigidity and shear strength to allow S-waves to travel through them. This is because the particles in a solid are closely packed and have strong intermolecular forces that resist deformation, enabling the shearing motion characteristic of S-waves.

Liquids, however, lack the rigidity and shear strength required for S-waves to propagate. In liquids, the particles are not as tightly bound as in solids, and the intermolecular forces are weaker. This means that when an attempt is made to propagate an S-wave through a liquid, the particles cannot sustain the shearing motion. Instead, they tend to move in the direction of the wave's propagation, which is characteristic of P-waves. As a result, S-waves cannot effectively travel through liquids and are not observed in this state of matter.

It's important to note that while S-waves cannot propagate through liquids, they can still be indirectly detected through the effects they have on the surrounding solid materials. For example, when an earthquake occurs, both P-waves and S-waves are generated. Seismographs can detect these waves, and the difference in arrival times can be used to estimate the distance to the earthquake's epicenter. The absence of S-waves at a particular location can indicate that the wave has traveled through a liquid layer, such as the Earth's outer core, which is in a molten state.

In summary, the propagation of S-waves is contingent upon the medium's ability to support shear stress. Solids can support this stress, allowing S-waves to travel through them, while liquids cannot due to their lack of rigidity and shear strength. This fundamental difference in material properties is what prevents S-waves from traveling through liquids.

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Why can't S-waves travel through liquids? S-waves are shear waves, which move particles perpendicular to their direction of propagation. They can propagate through solid rocks because these rocks have enough shear strength. ... This is why S-waves cannot propagate through liquids.read more >>