What causes earthquakes and how are they measured?

Earthquakes occur when stress builds up along tectonic plate boundaries and is suddenly released. 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.