Rock slowly deforms and stores energy like a spring.
Rock breaks at the fault and springs back!
Energy radiates out as seismic waves.
Mountains rise!
Earthquakes!
New ocean floor!
Get on hands & knees.
Under a sturdy desk!
Grip tight till it stops!
Rock bends → SNAPS → waves travel → buildings feel it → you know what to do: Drop, Cover, Hold On!
Core science: Elastic rebound theory (Reid, 1911). Tectonic forces slowly deform rock near a fault. When stress exceeds rock strength, it fractures and both sides spring back — releasing stored elastic energy as seismic waves. P-waves (compressional, ~6–8 km/s in granite) arrive first; S-waves (shear, ~3.5–4.5 km/s) cause most damage because they move ground perpendicular to propagation direction.
Plate tectonics: ~15 major plates float on the asthenosphere. Convection + slab pull + ridge push drive them at 2–10 cm/yr. Three boundary types: convergent, transform, divergent. ~90% of quakes occur at or near plate boundaries.
Magnitude: Moment magnitude (Mw) is logarithmic — each whole number ≈ 32× more energy. M 5 ≈ 32 kilotons TNT; M 9 ≈ 32,000 kilotons.
Real-world demos: ① Snap a ruler — feel the jolt. ② Glass of water on a book — slide = P-wave. ③ Slinky: push = P; flick sideways = S.
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