Question

S waves temporarily change the shape of the material that transmits them. Can you identify a place in Earth's interior that would not transmit S waves? Why?

Short answer

The Earth's outer core does not transmit S waves because it is liquid.

Step-by-step solution

Introduction to S Waves

S waves, or secondary waves, are a type of seismic wave that propagate through Earth during an earthquake. They are transverse waves, meaning they move the material perpendicular to the direction of wave travel, altering the shape of the material they move through. They require a medium that can resist changes in shape, such as solids.

Explaining Why S Waves Can't Transmit Through Fluids

S waves cannot travel through fluids like liquids or gases because these materials cannot support shear stress. Since fluids do not have a definite shape and cannot resist deformation, they do not transmit S waves.

Identifying a Part of Earth's Interior That Would Not Transmit S Waves

The Earth's outer core is a layer of the planet that consists primarily of liquid iron and nickel. Because it is in a liquid state, the outer core cannot support the shear stress that S waves require to propagate, meaning it does not transmit S waves.

Conclusion

Since S waves cannot travel through liquids, and the Earth's outer core is liquid, S waves are not transmitted through this part of the Earth's interior.

Key concepts

S Waves

S waves, also known as secondary waves, play a significant role in the study of seismic activities. Unlike P waves, which move in the same direction as the wave itself, S waves are transverse waves. This means they move the ground up and down or side-to-side, perpendicular to the direction of the wave.

For S waves to propagate, they require a medium that can resist shape changes, typically solid materials. These waves temporarily distort the shape of the materials they pass through. Therefore, materials or layers of the Earth that are solid allow S waves to travel through them.

Their inability to pass through liquids is a fundamental property, which is crucial when studying different layers within the Earth. Understanding S waves helps researchers map the structure and composition of the Earth’s interior, offering insights into its layers.

Earth's Outer Core

The Earth's outer core is a fascinating and important layer of our planet's interior. It consists mainly of liquid iron and nickel, making it the only part of the Earth's interior that is entirely in a liquid state. This is a key factor in its inability to transmit S waves.

Due to its fluid nature, the outer core cannot support the shear stress required for S waves to propagate. This occurs because fluids do not have a rigid shape; they cannot resist the change in form that S waves impose, as solids do.

The liquid outer core is not only critical to understanding seismic waves but also plays a crucial role in the generation of Earth's magnetic field. The movement of the liquid iron generates electric currents, which lead to the creation of the magnetic field surrounding the Earth.

• The outer core is about 2,300 kilometers thick.
• It extends from the mantle down to the inner core.

This composition and behavior make the outer core an intriguing subject of study for geoscientists worldwide.

Seismic Wave Propagation

Seismic wave propagation is essential for understanding the Earth's interior layers. Seismic waves are generated by earthquakes or artificial sources and travel through the Earth's layers, providing scientists with data about our planet's inner structure.

There are two main types of seismic waves: body waves and surface waves. Body waves, which include both P waves and S waves, travel through the Earth's interior. In particular, S waves require a solid medium and are unable to pass through liquid layers, such as the Earth's outer core.

• P waves, or primary waves, are compressional and can travel through solids, liquids, and gases.
• S waves only move through solids, as they rely on shearing motion.

By analyzing the propagation of these waves, scientists can infer the presence and properties of various layers within the Earth.

Changes in wave speed, reflection, and refraction of seismic waves provide insights into the Earth’s composition. This is how scientists identified the liquid outer core and have gathered information about the solid structure of the inner core.