Short answer: most earthquakes happen when rocks on opposite sides of a fault are forced by tectonic motion but temporarily stick because of friction. Stress builds until the fault slips suddenly. The released energy travels through Earth as seismic waves.
Plates move slowly; earthquakes happen quickly
Tectonic plates are always moving on geological timescales. Their boundaries and faults are rough, so motion is not always smooth. Sections can lock while surrounding crust keeps deforming.
When accumulated stress exceeds the frictional resistance, the locked section ruptures. The sudden motion launches waves that produce shaking at the surface.
Why aftershocks follow
A large rupture changes stress on nearby parts of the fault system. Those adjustments can trigger additional earthquakes—aftershocks—for days, months or even longer depending on the sequence.
Quick follow-ups
FAQ
Do tectonic plates stop moving between earthquakes?
No. Plate motion continues while some fault sections remain locked, allowing stress to build.
Are all earthquakes caused by plate boundaries?
Many are concentrated near plate boundaries, but earthquakes can also occur on faults within plates and from some human activities or volcanic processes.
Check the evidence
Sources
- What is an earthquake and what causes them? — U.S. Geological Survey
- The Science of Earthquakes — U.S. Geological Survey
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