Final answer:
S-waves, or Shear waves, can only travel through solids and are unable to travel through liquids or gases because they require a material's shear strength to propagate. The study of S-waves is crucial to understand Earth's interior composition, including the liquid outer core.
Step-by-step explanation:
Shear waves, also known as S-waves or Secondary waves, are a type of body wave that travels through the Earth during an earthquake. Unlike P-waves (Primary waves), which are compressional and can travel through solids, liquids, and gases, S-waves are transverse waves and can only propagate through materials that have shear strength. Based on seismic evidence and our understanding of wave propagation, it's established that S-waves cannot travel through fluids such as liquids and gases because these materials do not have the necessary shear strength to support the motion of transverse waves. For this reason, S-waves are only capable of travelling through solids.
Geologists and seismologists have been able to shed light on the composition of the Earth's interior by studying how these waves travel through different media, including the discovery that the Earth's outer core is liquid, as S-waves do not pass through it. Different materials can affect the speed of these waves: more rigid materials like granite allow both S-waves and P-waves to travel faster compared to less rigid materials like sediments. The absence of S-waves in certain parts of the Earth's shadow zones further backs the liquid core hypothesis, and the study of these waves is crucial for earthquake seismology.