Earth Science

Geological Activity from Plate Tectonics Processes

Earthquake Characteristics

Study Tip
The focus is farther underground than the epicenter.

Earthquakes

  • Earthquakes are sudden ground movements caused by the release of energy by rocks. This energy is transmitted by seismic waves.
  • The size of earthquakes and the damage they cause can vary greatly.
Study Tip
The focus is farther underground than the epicenter.
Study Tip
The same way a person may cast a shadow over another person when they stand under the sun, planets or celestial bodies that have aligned themselves cast shadows over one another as well.

The Elastic Rebound Theory

  • The elastic rebound theory describes how earthquakes are generated.
  • Stresses on both sides of a fault cause strain to build up in rocks, until they can no longer bend elastically.
  • Once the stress is too great, the rocks break, releasing the built up energy and creating an earthquake.
The elastic rebound theory
The elastic rebound theory tells us how the faults start to bend and change.

Focus and Epicenter

  • The initial point where the rocks rupture in the crust is called the focus.
  • The point on the land surface that is directly above the focus is called the epicenter.
  • Shallow earthquakes can cause the most damage because the focus is nearer to the surface.
he energy from earthquakes moves outwards
The energy from earthquakes moved outwards from the focus.
Concept Check
  • How are earthquakes formed? How is the energy transferred?
  • What is the difference between the focus and the epicenter?