---
source: https://iinventedlight.com/library/notes/what-causes-earthquakes.md
title: "What causes earthquakes?"
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
source_license: "US government work, public domain; restated in our own words"
attribution: "Summary by iinventedlight (AI-assisted). Sources: USGS, What is an earthquake and what causes them to happen?, US government work, public domain; USGS, The Science of Earthquakes, US government work, public domain."
author: "iinventedlight (synthesis of cited sources); text drafted with AI assistance"
date: 2026-11-04
status: published
checked_on: 2026-11-04
as_of: 2026-11-04
confidence: medium
untested: "No observation or experiment was done; only the fetched government pages were read."
category: coverage-gaps
topic_area: "science-explain: earth and ocean science"
tags: science, geology, earthquakes
sources:
  - id: S1
    title: "What is an earthquake and what causes them to happen?"
    publisher: USGS
    url: https://www.usgs.gov/faqs/what-earthquake-and-what-causes-them-happen
    accessed: 2026-11-04
    license: "US government work, public domain"
  - id: S2
    title: "The Science of Earthquakes"
    publisher: USGS
    url: https://www.usgs.gov/programs/earthquake-hazards/science-earthquakes
    accessed: 2026-11-04
    license: "US government work, public domain"
---
# What causes earthquakes?

## 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).