What causes earthquakes and how are they measured?

Process:

1. Earth's crust is divided into tectonic plates that float on the mantle
2. Plates move slowly (2–10 cm/year), creating stress at boundaries
3. When friction is overcome, plates slip suddenly → earthquake
4. Energy radiates outward as seismic waves

Types of plate boundaries:

• Convergent (plates collide) — strongest earthquakes
• Divergent (plates pull apart)
• Transform (plates slide past each other) — e.g., San Andreas Fault

Measurement: The Richter scale measures magnitude logarithmically. Each whole number = 10× more ground motion and ~31.6× more energy. A magnitude 7 is 1,000 times stronger than a magnitude 5.