Earthquakes

1. Earthquakes & Faults

• Earthquakes are vibrations caused by the release of energy along faults.

• Elastic Rebound: Stress builds, rocks snap back to original shape, releasing energy.

• Include foreshocks, aftershocks, and sometimes fault creep (slow, gradual movement).

2. Seismology

• Seismic waves are recorded with seismographs, producing seismograms.

• Types of Waves:

  • P-waves: Fast, compressional, travel through all materials.

  • S-waves: Slower, shear motion, only through solids.

  • Surface waves: Slowest, most destructive, move ground up/down or side to side.

3. Earthquake Location

• Focus (hypocenter): Underground origin.

• Epicenter: Surface point above focus.

• Located using triangulation of body wave arrival times.

• Shallow foci = any boundary; Deep = typically subduction zones.

4. Measuring Earthquakes

• Intensity (Modified Mercalli): Measures damage (qualitative).

• Magnitude:

  • Richter Scale: Based on wave amplitude (logarithmic, 32x energy per unit).

  • Moment Magnitude: Based on fault displacement; better for large quakes.

5. Earthquake Damage

• Influenced by: Intensity, duration, ground material, and building design.

• Hazards include:

  • Liquefaction

  • Tsunamis

  • Mass wasting (landslides)

• Prediction is currently not possible.

6. Earth’s Interior (from Seismology)

• Seismic waves help map Earth’s layers:

  • Crust: Thin outer layer; thicker under continents than oceans.

  • Mantle: Peridotite rock; includes soft asthenosphere and solid lower mantle.

  • Core:

    • Outer core: Molten iron-nickel; causes magnetic field.

    • Inner core: Solid iron.

• Key Features:

  • Mohorovičić Discontinuity (Moho): Crust-mantle boundary.

  • Shadow Zone: Area where S-waves don't arrive due to liquid outer core.