key terms

• seismic hazards


  Generated when rocks within 700 km of the Earth's surface come under such stress that they break and

  become displaced.
• Volcanic hazards


  Associated with eruption events.
• Intra-plate earthquakes


  These occur in the middle or interior of tectonic plates and are much rarer than boundary earthquakes.
• Volcano


  A landform that develops around a weakness in the Earth's crust from which molten magma, volcanic rock,

  and gases are ejected or extruded.
• Plate tectonics


  A theory developed more than 60 years ago to explain the large-scale movements of the lithosphere
• Lithosphere


  The surface layer of the Earth is a rigid outer shell composed of the crust and upper mantle. It is on average

  100 km deep.
• Paleomagnetism


  Results from the zone of magma 'locking in' or 'striking' the Earth's magnetic polarity when it cools. Scientists

  can use this tool to determine historic periods of large-scale tectonic activity through the reconstruction of

  relative plate motions. They create a geo-timeline.
• Subduction zones


  These are broad areas where two plates are moving together, often with the thinner, more dense oceanic

  plate descending beneath a continental plate.
• Locked fault


  A fault that is not slipping because the frictional resistance on the fault is greater than the shear stress across

  the fault, that is, it is stuck.
• Hypocentre


  This is the 'focus' point within the ground where the strain energy of the earthquake stored in the rock is first

  released. The distance between this and the epicentre on the surface is called focal length.
• Soil liquefaction


  The process by which water-saturated material can temporarily lose normal strength and behave like a liquid

  under the pressure of strong shaking.
• Intensity


  A measure of the ground shaking.
• Magnitude


  the amount of movement, or displacement, in the fault, which is

  in turn a measure of energy release.
• Epicentre


  The location on the Earth's surface that is directly above the earthquake focus, i.e. the point where an

  earthquake originates.
• Hazard


  a naturally occurring process or event that has the potential to affect people
• disaster


  a major natural hazard that causes significant social, environmental and economic damage
• Risk


  the probability of a hazard occurring that leads to the loss of lives and/or livelihood.
• Resilience


  the ability of a system, community or

  society exposed to hazards to resist, absorb and recover from the effects of a hazard.
• Tectonic hazard profile


  A technique used to try to understand the physical characteristics of different types of hazards, for example earthquakes, tsunamis and volcanoes.
• Disaster hotspot


  A country or area that is extremely disaster prone for a number of reasons.