Earthquake Generation

• Earthquakes are vibrations of the ground created as seismic waves pass a point of the Earth’s surface or interior. Smaller magnitude earthquakes can be created by massive landslides, meteorite impacts, and nuclear testing.
• Volcanic Earthquakes - caused by movement of lava under volcanoes or magma fissures.

  Tectonic Earthquakes - created by movement of faults or planes.
• Elastic Rebound Theory - explains how energy that powers earthquakes are built up and dissipated as seismic waves.

  -The theory posits that rocks making up the lithosphere can tolerate a limited amount of deformation until it reaches its elastic limit.

  -Materials can be bent and deformed and spring back to their initial state until a certain degree.

  -When they reach their elastic limit, they will have a permanent change in their shape or even break when additional force is applied.
• Rocks lock up, bend, and crumple within the fault and plate boundaries as stress and strain build up in the area.
• Stress and strain accumulate large amounts of elastic energy in time until rocks in the region reach their elastic limit. When this happens, rocks start to break and slip. Energy is then released as rocks spring back to their original shape, much like rubber bands spring back to their old shape after being stretched. The energy travels outwardly from the point of origin or focus to other locations on the Earth as seismic waves which are experienced as earthquakes.
• The build-up of elastic potential energy in a fault happens over a long time. This is usually related to the recurrence interval of earthquakes in a fault line.

  Recurrent interval - average time between consecutive earthquakes in a location. The longer it is, the higher stored energy in the region, which means a higher probability of large-magnitude earthquakes in the area.
• Seismic waves carry the energy from the focus of an earthquake to other parts of the Earth. Seismic waves that pass through the Earth’s interior are called body waves (e.g. primary waves, secondary waves). On the other hand, surface waves (Rayleigh waves, love waves) are seismic waves that travel on the surface.
• Body Waves:

  • Primary Waves - can travel through solids, liquids, and gases.

  - travel faster than S waves

  - moves horizontally

  • Secondary Waves - can only travel through solids

  - travels slower than P waves, creating more damage to the area

  - moves vertically
• Surface Waves:

  • Rayleigh Waves - move in a circular motion and are more destructive than love waves
  • Love waves - move side-to-side and are faster than rayleigh waves