Earth's Interior

Seismic Waves

• Earthquakes produce energy that is transmitted through the Earth in the form of seismic waves.

  • Two main types of seismic waves: pressure waves (P waves) and shear waves (S waves).

Pressure Waves (P Waves)

• Also known as primary waves.

• Can travel through solids, liquids, and gases.

• Analogous to compressing and expanding a slinky: moves materials by creating regions of compression and expansion.

• Fastest seismic wave; can move in all directions through the Earth.

• Helpful in analyzing the interior of the Earth since they can be detected all around the planet after an earthquake.

Shear Waves (S Waves)

• Can only travel through solids and cannot pass through liquids or gases.

• Movement resembles an up-and-down motion, contrasting with the compressive movement of P waves.

• The speed of S waves is influenced by the density of the material they move through.

Analyzing Earth's Interior

• The speed and behavior of P and S waves provide insights into the Earth's internal structure.

• When P waves are detected worldwide following an earthquake, it shows their traversable path through the Earth.

• The absence of S waves in certain areas creates "shadow zones," suggesting the presence of liquid layers in the Earth, specifically the outer core. This leads to the understanding that:

  • The outer core is liquid, as it does not transmit S waves.

  • The mantle is less dense than the core and is assumed to be rocky.

  • The core is thought to be metallic, primarily composed of an iron and nickel alloy.

• The Earth has two core sections:

  • Outer Core: Liquid phase.

  • Inner Core: Solid phase, maintained by high pressure rather than low temperature.

Evidence from Lava and Moonquakes

• The analysis of lava that surfaces from the mantle supports the rocky composition of the mantle.

• The Moon experiences "moonquakes," which, although weaker than earthquakes, provide enough data to analyze its internal structure.

• Data from the Moon indicates:

  • Presence of a core, mantle, and crust similar to Earth.

  • Density of the Moon's material is similar to that of Earth, but there are chemical differences.