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Short answer

An earthquake is a sudden slip on a fault. Tectonic plates keep moving slowly but stick at their edges from friction; when the stress beats the friction, the stored energy is released as seismic waves that shake the ground. [S1][S2]

Words to know

• Fault: the surface where two blocks of earth slip. [S2]
• Hypocenter: where the quake starts underground; the epicenter is the spot on the surface directly above. [S2]
• Foreshock / aftershock: relative terms; a quake is only a foreshock if a bigger one follows. [S1]

Claims

• id: C1 claim: An earthquake is caused by a sudden slip on a fault. source: S1 evidence: "An earthquake is caused by a sudden slip on a fault."
• id: C2 claim: Foreshocks precede larger earthquakes in the same location. source: S1 evidence: "Foreshocks are earthquakes that precede larger earthquakes in the same location."
• id: C3 claim: An earthquake is two blocks of earth suddenly slipping past each other. source: S2 evidence: "two blocks of the earth suddenly slip past one another"
• id: C4 claim: Where the earthquake starts is called the hypocenter. source: S2 evidence: "where the earthquake starts is called the hypocenter"

Sources

• [S1] What is an earthquake and what causes them to happen?. USGS. https://www.usgs.gov/faqs/what-earthquake-and-what-causes-them-happen . License: US government work, public domain. Accessed 2026-11-04.
• [S2] The Science of Earthquakes. USGS. https://www.usgs.gov/programs/earthquake-hazards/science-earthquakes . License: US government work, public domain. Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

@misc{iil_note_vtr67qh1,
  author = {{iinventedlight}},
  title = {{What causes earthquakes?}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/what-causes-earthquakes/},
  note = {Permanent ID iil:note:vtr67qh1. License: CC-BY-4.0.},
}

Markdown

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