Geography – Earthquake and volcanic hazards and impacts | e-Consult

As seismic waves radiate outwards from the hypocentre, their behaviour is significantly influenced by the Earth's internal structure.

Propagation of Waves through Earth's Layers:

• Crust: P and S waves travel through the crust, but their speed is affected by the varying composition and density of the crustal rocks. Love and Rayleigh waves are confined to the crust.
• Mantle: P and S waves travel through the mantle, but their speed increases with depth due to the higher density of the mantle rocks. The mantle is mostly solid, but has a plastic-like behaviour over long timescales.
• Outer Core: P waves cannot travel through the liquid outer core, creating a significant shadow zone. S waves are also significantly attenuated in the outer core.
• Inner Core: P and S waves can travel through the solid inner core. The inner core causes a further shadow zone for S waves.

Wave Paths and Interaction with Earth's Structure:

• P Waves: Travel in straight lines, refracting (bending) as they pass through boundaries between layers with different densities. Refraction occurs due to changes in the speed of the waves.
• S Waves: Travel in straight lines, but are blocked by the liquid outer core. This creates a large shadow zone.
• Love Waves: Propagate horizontally and are most effective in the crust. They are refracted at boundaries between layers with different rigidity.
• Rayleigh Waves: Propagate along the Earth's surface and are influenced by the depth of the Earth's surface and the properties of the underlying layers. They are refracted at the Earth's surface and at boundaries between layers with different densities.

Diagram:

[Image missing: Seismic Waves Diagram]