SEISMIC WAVES and EARTH'S INTERIOR

Behavior of Waves

• Reflection
• Refraction

Seismic Stratigraphy

Behavior of Seismic Waves

• Average density of Earth (5.5 gm/cm³)
• More than crust and mantle
• Seismic wave velocities (shadow zones)
• Composition of meteorites
• Laboratory experiments
• Chemical stability
• Seismic velocities
• Earth’s magnetic field

Seismic Wave Velocities

Earth's Interior

• 1909 - Mohorovicic velocity of P-waves increase abruptly at ~50 km
• The Mohorovicic discontinuity (Moho) is the boundary between crust and mantle

The Mantle

• ~2900 km thick
• S-wave velocities vary with depth
• constituents and density vary with depth
• structure of materials varies with depth (Fig. 10-35)

Structure of the mantle from S-wave velocities

• Layered
• Low velocity zone (LVZ ) - partially molten
• Olivine structure - peridotite

The Mantle (cont.) 
Seismic Tomography

The Core

• P- and S- wave shadows (Fig. 17.10)

• Outer Core
• Liquid Fe with Ni, S, O, and/or Si
• Evidence:
• shadow zone
• magnetic field