Tectonics -PMT

• A hazard is a potential threat to human life and property
• Natural hazard


  Can be either hydro-meteorological or geophysical
• Geophysical hazards

  Occur near plate boundaries

  
• Plates move at different speeds and directions which can cause collisions, earthquakes and volcanic activity

  
• Earthquakes can also occur near the middle of plates (called intra-plate)
• The causes of intraplate earthquakes are not fully understood

  
• Intraplate earthquakes

  Assumed that plates have pre-existing weaknesses which become reactivated
• An intraplate earthquake may occur if solid crust, which has weakened over time, cracks under pressure
• Volcanic hotspots


  Localized areas of the lithosphere with unusually high temperature due to upwelling of hot molten material from the core
• The Ring of Fire is an example of a volcanic hotspot
• Magma rises as plume (hot rock) at hotspots
• The most powerful earthquakes usually occur at convergent or conservative boundaries
• OFZ (Oceanic Fracture Zone) is a belt of activity through the oceans and along the mid-ocean ridges

  
• CFZ (Continental Fracture Zone) is a belt of activity along the mountain ranges from Spain through the Alps to the Middle East and to the Himalayas

  
• The total number of recorded hazards has increased since 1960
• The number of fatalities has decreased since 1960, but there are spikes during mega disasters
• The total number of people being affected by tectonic hazards is increasing due to population growth
• The economic costs associated with hazards and disasters have increased significantly
• Increases in development as infrastructure in more developed countries costs more to repair contribute to rising economic costs
• Increasing number of insurance policies, especially in developed countries, heightens the costs
• Reporting disaster impacts is difficult and controversial for several reasons
• Reasons reporting disaster impacts is difficult

  • Direct deaths
  • Indirect deaths
  • Location
  • Different methods
  • Government bias
• Direct deaths refer to those killed in the disaster straight away
• Indirect deaths refer to how many people died of diseases that spread after the disaster
• The location is important as rural and isolated areas are hard to reach
• Data may be difficult to collect in areas with very high population densities
• Different methods may be used by different organisations, leading to different numbers of deaths and injuries
• The number of deaths quoted by a government could be subject to bias
• The 2004 Indian Ocean tsunami is an example of government bias in reporting deaths

  
• Sections of the Earth

  • Crust
  • Mantle
  • Outer Core
  • Inner Core

  
• Crust

  Uppermost layer of the Earth, thinnest, least dense and lightest

  
• Oceanic crust is only 7km thick, whereas continental crust can be up to 70km thick

  
• Mantle

  Largely composed of silicate rocks, rich in iron and magnesium, semi-molten
• The mantle is at a depth from 700km to 2890km below the crust
• Outer Core

  Dense, semi-molten rocks containing iron and nickel alloys
• The outer core is at a depth of 2890km to 5150km below the Earth’s surface
• Inner Core

  Similar composition to the outer core, solid due to extreme pressures
• The inner core is over 5150km below the Earth’s crust

  
• The core’s high temperature is a result of primordial heat and radiogenic heat

  
• Types of plate boundaries

  • Destructive
  • Constructive
  • Conservative