Earthquake Lecture Notes

Introduction

• Focus on earthquakes: causes, types, prediction, and safety measures.
• Importance of understanding earthquakes, especially after the recent event in Turkey.

Earth Structure

• Formation: Earth started as molten rock; crust formed as it cooled.
• Crust: 8-40 km thick; rests above the liquid mantle.
• Tectonic Plates: Earth's crust is divided into tectonic plates which are in constant motion.
• Faults: Cracks occur where plates collide, leading to earthquakes.

What is an Earthquake?

• Earthquake = shaking of Earth's surface due to pressure build-up at faults.
• Epicenter: Area where earthquake is felt most strongly.
• Seismic Waves: Diminish with distance from the epicenter.
• Frequency: Around 55 perceptible earthquakes daily with many more detected by instruments.

Earthquake Strength

• Richter Scale: Measures earthquake energy; invented by Charles Richter in 1935.
• Magnitude: No upper limit theoretically; 10+ is catastrophic.
• Intensity vs. Magnitude:
  • Intensity: How an earthquake is felt on the ground (Mercalli scale).
  • Magnitude: Energy released (Richter scale).

Earthquake Measurement

• Seismograph: Instrument used to measure earthquakes.
• Historical Seismographs: Early pendulum design; modern versions are digital and more accurate.

Types of Earthquakes

• Horizontal vs. Vertical:
  • Horizontal: More destructive, causes whiplash effect.
• Volcanic & Underwater: Can cause tsunamis (e.g., Japan 2011).

Earthquake Prediction

• Prediction Limitations: Exact location and time are unpredictable.
• Animal Behavior: Some animals may sense imminent earthquakes.

Historical Earthquakes

• Strongest: 1960, Valdivia, 9.5 magnitude.
• Deadliest: 1976 earthquake with 242,000 victims.

Earthquake Prone Areas

• Pacific Ring of Fire: Most active zone, responsible for 90% of earthquakes.

Earthquake Safety Tips

• During an Earthquake:
  • Stay calm.
  • Hide under a desk or table.
  • Avoid windows and heavy objects.
  • Do not use elevators.
• Preparation:
  • Keep a survival kit ready.

Aftershocks

• Occur as Earth's crust adjusts post-main quake.
• Can be dangerous if structures are already damaged.

Regional Concerns: Bulgaria

• Concerns about a major earthquake are unscientific predictions.
• Buildings post-1988 are built to withstand significant earthquakes.

Conclusion

• Encouragement to stay informed and prepared.
• Options for further learning and engagement.