Geology and Earthquakes Lecture Notes

Introduction

• Earthquakes are demonstrations of energy moving through the Earth.
• Analogies: energy waves in water, ringing bell.
• Epicenter: surface location directly above the earthquake's energy release.
• Focus: point within the Earth where energy is released.

Seismic Waves

• Seismic Waves: waves that move out from the focus in all directions.
• Types of seismic waves:
  • Body Waves
    • Travel through the Earth's interior.
    • Two types:
      • P-Waves (Primary Waves): fastest, move in a compress-and-stretch manner.
      • S-Waves (Secondary Waves): slower, move in a side-to-side motion.
  • Surface Waves
    • Travel along the Earth's surface.
    • Two types:
      • Rayleigh Waves: cause ground to roll like ocean waves, less destructive.
      • Love Waves: more destructive, cause side-to-side motion.

Wave Characteristics

• P-Waves: primary warning, less destructive.
• S-Waves: follow P-Waves, moderately destructive.
• Surface Waves: most destructive, arrive after P and S waves.
• Seismic Wave Impact on Buildings
  • Earthquakes themselves don't kill, but collapsing buildings do.

Wave Properties

• Refraction: bending of waves towards lower density; similar to a mirage.
• Reflection: bouncing of waves; discovered with Moho.
• Moho (Mohorovicic Discontinuity): reflective surface within the Earth.

Case Study: San Francisco Earthquake 1989

• Reflection and refraction intensified shaking, causing significant damage.

Wave Interaction with Fluids

• P-Waves: can travel through fluids (liquid or gas).
• S-Waves and Love Waves: cannot travel through fluids.
• Rayleigh Waves: can roll through fluids, similar to water waves.

Conclusion

• Body waves act like x-rays for examining the Earth's interior.⭕️