🔹 What Causes Earthquakes?
Tectonic Plate Movement (Most Common Cause)
The Earth’s outer shell (lithosphere) is divided into large sections called tectonic plates.
These plates move slowly over the semi-fluid mantle.
At their boundaries, plates can:
Collide (convergent boundary)
Slide past each other (transform boundary)
Pull apart (divergent boundary)
The stress builds up over time and is suddenly released as an earthquake when the rocks break or slip along a fault.
Volcanic Activity
Magma movement beneath volcanoes can cause smaller, localized earthquakes.
These are common in volcanic regions like the Pacific "Ring of Fire."
Human Activities (Induced Earthquakes)
Large dams, mining, oil drilling, and fracking can also trigger earthquakes.
🔹 Key Terms
Focus (Hypocenter): The point underground where the earthquake starts.
Epicenter: The point on the Earth's surface directly above the focus.
Fault: A crack in the Earth's crust where movement occurs.
Seismic Waves: Energy waves that travel through the Earth and cause shaking.
🔹 Measuring Earthquakes
Magnitude: Measures the energy released (Richter scale, Moment Magnitude Scale - Mw).
Intensity: Measures the effects felt by people and structures (Modified Mercalli Intensity scale).
🔹 Earthquake Effects
Ground Shaking
Surface Rupture
Landslides
Tsunamis (if undersea earthquake)
Building Collapse and Infrastructure Damage
Aftershocks — smaller quakes following the main one
🔹 Famous Earthquakes
2004 Indian Ocean Earthquake (Magnitude 9.1): Triggered a massive tsunami.
2011 Japan Earthquake (Magnitude 9.0): Caused a tsunami and Fukushima nuclear disaster.
1906 San Francisco Earthquake: Devastated the city and changed urban planning in the U.S.
🔹 Earthquake Safety Tips
Before: Secure furniture, make an emergency plan, and have a survival kit.
During: Drop, Cover, and Hold On. Stay away from windows.
After: Check for injuries, gas leaks, and follow emergency instructions.
