Overview
This lecture explains what earthquakes are, their causes, how they work, and the science behind their measurement and effects.
What is an Earthquake?
- Earthquakes occur when energy is suddenly released in the Earth's crust, generating waves that shake the surface.
- The Earth's outer layer is made of 19-20 moving tectonic plates, like a jigsaw puzzle.
- Most movements are too small to feel, but strong ones cause noticeable shaking or destruction.
Earthquake Structure and Terminology
- The focus point under the Earth where an earthquake starts is the hypocenter.
- The surface point directly above the hypocenter is the epicenter.
- Earthquakes primarily occur in the Earth's lithosphere layer.
Measuring Earthquakes
- Seismic waves generated by tectonic movement are detected by a device called a seismograph.
- Earthquake strength is measured on the Richter scale, from 0 (not felt) to 10 (massive destruction).
- Magnitude categories: 0-2 (barely sensed), 2-4 (minor vibrations), 4-4.9 (light), 5-5.9 (moderate), 6-6.9 (strong), 7+ (major).
Earth's Layers
- Inner core: solid sphere, radius ~1250 km, 4500-5500°C, high pressure.
- Outer core: liquid, ~2200 km thick, similar temperature to inner core.
- Mantle: semi-solid, ~2900 km thick, 84% of Earth's volume.
- Crust: outermost layer, 0-70 km thick, only 1% of Earth's mass.
Earthquake Waves
- Body waves travel through Earth's interior; includes primary (P) waves and secondary (S) waves.
- P waves shake the ground back and forth in the wave direction; first to arrive at seismographs.
- S waves move the ground perpendicular to wave direction; cause tremors and are felt after P waves.
- Surface waves travel along the crust and cause the most damage to structures.
Earthquake Damage Examples
- Magnitude 4-4.9: light damage, mainly to small houses.
- Magnitude 5-5.9: moderate damage, cracks in buildings and roads.
- Magnitude 6-6.9: severe damage, buildings collapse, major road damage.
- Higher magnitudes can destroy entire cities.
Earthquake Prediction and Safety
- Prediction is difficult with current seismographs or seismometers.
- New tech, including smartphones, can detect seismic waves and help warn people.
- NASA uses QuakeSim software for advanced earthquake data analysis.
- High radon and thoron gas detection may give up to 7 days warning before a quake.
Key Terms & Definitions
- Tectonic plates — Large, moving slabs of Earth's crust.
- Hypocenter — Underground point where an earthquake begins.
- Epicenter — Surface point directly above the hypocenter.
- Seismic waves — Vibrations caused by energy released during an earthquake.
- Seismograph — Device for detecting and recording seismic waves.
- Richter scale — Measurement scale for earthquake magnitude (0-10).
- P waves (Primary waves) — Fastest body waves; move through solids and liquids.
- S waves (Secondary waves) — Slower body waves; move only through solids.
- Surface waves — Travel along the Earth's crust, causing most damage.
Action Items / Next Steps
- Review earthquake safety tips.
- Explore 3D simulation tools like Scholar by Escobel for interactive learning.
- Observe earthquake magnitude and response using simulation software if available.