Skip to main content

Mechanism of earthquake

Short answer

Tectonic stress bends locked fault rocks, storing elastic strain energy. When stress exceeds strength, rupture occurs and rocks rebound, releasing seismic waves from the focus; the epicenter is the surface point above it.

Describe the mechanism of earthquake.

An earthquake is a sudden shaking of the ground caused by the release of stored strain energy in the Earth's crust.

Elastic rebound theory (H. F. Reid, 1910, after the 1906 San Francisco earthquake)

  1. Tectonic forces (plate movements) act slowly on rocks along a fault.
  2. Friction locks the fault, so the rocks bend and strain energy is stored, like a stretched spring.
  3. When the stress exceeds the strength of the rock or the friction, the rock suddenly breaks or slips.
  4. The rocks spring back (rebound) to a less strained position and the stored energy is released as seismic waves.
  5. The waves travel outward and shake the ground. After the main shock, readjustment causes aftershocks.
 Before        Strain         After slip
 |  |  |       \  \  \        |  |  |
 |  |  |        \  \  \       |__|__|
 straight       bent         rebound,
                             fault slip

Related terms

  • Focus (hypocentre): point of rupture inside the Earth.
  • Epicentre: point on the surface directly above the focus.

Most earthquakes occur on plate boundaries, such as the Himalayan collision zone, which produced the 1934 Nepal-Bihar and 2015 Gorkha earthquakes.

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Engineering Geology I chapter 2 questions →