Lecture Notes: Earth's Interior and Seismic Waves

Earth's Layers

• Three Main Layers: Crust, Mantle, Core
  • Crust: Outermost layer
  • Mantle: Below the crust
  • Core: Innermost layer

Evidence of Earth's Composition

• Xenoliths: Rocks from the upper mantle
• Ophiolites: Pieces of ancient oceanic crust and upper mantle
• Kimberlite Pipes: Volcanic eruptions bringing mantle pieces to the surface
• C1 Chondrite Meteorites: Provide insight as Earth's parent material

Seismic Waves

• Definition: Vibrations through Earth, studied by seismologists
• Types of Waves:
  • Surface Waves: Travel through shallow crust
    • Love Waves: Side-to-side motion
    • Rayleigh Waves: Rolling motion
  • Body Waves: Travel through Earth's interior
    • P Waves (Primary): Compressional, fastest (8 km/s)
    • S Waves (Secondary): Shear, slower (3.5 km/s)

Seismic Waves and Earth's Interior

• Seismic Echogram: Created by measuring seismic waves
• Wave Interaction: Affected by density, temperature, state of rocks
• Shadow Zones:
  • S-Wave Shadow Zone: Indicates outer core is liquid
  • P-Wave Shadow Zone: Caused by refraction at core-mantle boundary

Earth's Sub-Layers and Discontinuities

• Mohorovicic Discontinuity (Moho): Increase in density between crust and mantle
• Low Velocity Zone: Transition to ductile rocks (asthenosphere)
• Lithosphere: Includes crust and upper mantle
• Asthenosphere: Ductile layer where mantle flows
• Transition Zone: Between 410 km and 660 km depth, changes in olivine structure
• Lower Mantle (Mesosphere): Steady increase in seismic velocities
• D-double Prime Layer: Low seismic velocities, potential partial melting

Core-Mantle Boundary

• Core-Mantle Boundary: At 2,889 km, disappearance of S-waves, slowing of P-waves
• Outer Core: Liquid state
• Inner Core: Solid state, P-wave velocity increase

Plate Tectonics

• Tectonic Plates: Continents-sized slabs of lithosphere
• Earthquakes & Volcanic Activity: Occur at tectonic plate boundaries
• Convection Patterns: Influenced by subducted slabs

These notes encapsulate the key points discussed regarding Earth's structure, seismic waves, and related geological phenomena.