## TL;DR

Earthquakes occur when tectonic plates suddenly slip along faults, releasing accumulated stress as seismic waves. Measured by seismographs. Magnitude scales: Richter (local, historical), Moment Magnitude (Mw, modern — logarithmic: each 1.0 increase = 32x more energy). Largest recorded: 1960 Chile (Mw 9.5).

## Core Explanation

Epicenter: point on surface above focus (hypocenter). P-waves (primary, fast, compressional), S-waves (secondary, slow, shear — can't travel through liquid). Surface waves: cause most damage. Ring of Fire: 90% of earthquakes. Tsunami: earthquake displaces ocean water → massive waves. Early warning: seconds to minutes before shaking (Japan, California). 'Earthquakes don't kill people, buildings do' — engineering saves lives.

## Further Reading

- [Earthquakes (Bolt, 5th Ed)](https://us.macmillan.com/books/9780716756187/earthquakes)