1.3A

• Earthquakes are a sudden release of stored energy:​

  A pulse of energy radiates out in all directions from the earthquake focus (point of origin).

  The epicentre is the point on the Earth's surface directly above the focus.

  In some cases, the earthquake motion displaces the surface, so a fault scarp can be seen.
• P-Waves

  Primary waves

  The fastest, (rate of about 8 km/sec) so they arrive first

  Cause the least damage

  S and L waves have a larger amplitude and energy force

  They are vibrations causes by compression (like a shunt through a line of connected train carriages)
• S-Waves

  Secondary waves

  Arrive next (about 4 km / sec)

  Shake the ground violently, causing damage
• L-Waves

  Love waves

  Arrive last, as they travel only on the surface- 'vibration occurring in the horizontal plane'

  They have a large amplitude and cause significant damage, including fracturing the ground surface.

  The overall severity of an earthquake is linked to the amplitude and frequency of these wave types. 
• Crustal Fracturing

  Earthquakes cause crustal fracturing within the Earth, but also buckle and fracture the ground surface. 

  Some very large earthquakes, such as the one that generated the 2004 Indian Ocean tsunami, rupture a fault line for up to 1000 km.

  This can be though of as 'unzipping' a fault, with energy pulses being generated along the entire fault length.

  Such earthquakes can cause ground shaking that lasts up to 5 minutes, as well as dozens of powerful aftershocks. 
• ​Secondary Hazards

  Earthquakes frequently generate large landslides as secondary hazards. This is especially true in area of geologically young (and therefore unstable) mountains such as the Himalaya. Landslides accounted for up to 30% of the deaths in the 2008 Sichuan and 2005 Kashmir earthquakes. 
• Liquefaction is a particular hazard in areas where the ground consists of loose sediment such as sand, silt or gravel that is also waterlogged - often found in areas close to the sea or lakes. 

  Intense earthquake shaking compacts the loose sediment together, forcing water between the sediment out and upwards. This undermines foundations, and causes buildings to sink, tilt and often collapse. 

  In some earthquakes (e.g. Japan (2011?)) tilts of up to 60 degrees have been recorded. 

  It causes water-saturated material to temporarily lose normal strength and behave like a liquid under the pressure of strong shaking. Water pressure increases to the point where the soil particles can move easily.

  The effects of this are:

  damage to roads and bridges, as well as telecommunications