• Created by: Tooth04
  • Created on: 16-02-22 12:34

1.2 C tectonics

Benioff zone - is an area of seismicity corresponding with the slab being thrust down into the subduction zone. The different speeds and movement of rocks produces numerous earthquakes at this point. 

Subduction zones - broad areas where two plates are moving together either in a convergent or conservative plate boundary. 

-Locked fault - a stuck fault as the frictional resistance is greater than the sheer stress across the fault. Stuck faults can remain for extended periods of time where release causes a large magnitude earthquake ( aka a megathrust earthquake) e.g. Boxing Day 2004 tsunami.

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Secondary Hazards

Secondary Hazards of earthquakes:

  • Soil liquefaction - the process where water saturated material can temporarily lose strength and behave like liquid due to strong ground shaking. Can cause lateral spreading that creates fissures and cracks in the grounds surface. 
  • -ST impact - damage of roads and collapse of buildings could limit delivery of aid.                    
  • -LT impact - substantial rebuild costs.

Landslides - where slopes weaken and fall, rarely occur when magnitude is less than 4. 

Example ; Rockfall due to landslide halted river flow in Kali Gandaki river, Nepal. 70% of all earthquake deaths come from landslides, that can often travel several miles from thier source and grow by picking up natural debris. 

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A  tsunami is a series of waves caused by sea bed displacement, growing in height as they get closer to the shoreline due to raising ground. 90% found in the Pacific Basin, mostly generated at subduction zones. 

-Rapid movemnt of sea floor displaces of a water column and forces it upwards. 

-Water movement on the sea floor pushes other water outwards that beging to form waves. 

-As water moves towards the shore, the land height increases which increases wave height.

-As the waves get closer the water on the beach recedes which causes the wave crest to catch up to the foot of the wave and crash. (Normally 4th wave is biggest). 

  • Impact depends on;
  • Duration of event
  • presence of ecosystme buffers etc. Mangroves , Coral reefs
  • Timing of event - night/day- or quailty of early warning systems 
  • Degree of coastal development. 
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1.4C Social and economic impacts

-Impacts of tectonic hazards varies considerably from time to geographical region, which mary vary from minor nuisance to major disaster. 

-Disaster is categorised by; a significant impact on a population or 10 killed or 100 affected.

-The impacts of earthquakes (p and s) are usually much greater than those of volcanoes. The concentration of volcanoes across narrow belts means minimal area and populations are exposed to such a hazard (>1% is likely to be affected by volcanoes compared to earthquakes 5%). 

  • Economic impacts are proportional to land area exposed (earthquake wins out). However needs to be set against context;
  • level of development (region or country)
  • insured impacts vs non-insured
  • resilience of the population e.g. economic recovery post TH.
  • degree of urbanisation and linked interdependence.
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Hazard profile

-A hazard profile compares the physical process that all hazards share and helps decision makers to indentify and rank the hazards that should be given the most attention and resources. 

  • They look at:
  • Magnitude - enormous to just abover normal
  • Speed of onset - rapid to slow 
  • Duration - long to short
  • Areal extent - widespread to limited 
  • Spatial predictability - random to predictable 
  • Frequency - frequent to very rare 
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The 2004 Indian ocean tsunami

-earthquake off the coast of Sumatra (INDO) that caused a tsunami, estimated at 9.0 to 9.3 magnitude. 

  • -Impacts;
  • In some coastal areas, 70% of the population were killed (S).
  • In Sumatra, 1500 villages were completely destroyed (S).
  • In Sri Lanka, 60% of fishing fleet and industry infastructure was destroyed (E). 
  • In THAI, tourism industry lost US$25 million and 150,000 workers lost thier jobs (E).
  • Ecosystems such as coral reefs and coastal wetlands were severly damaged (EN) 
  • Most vegetation and topsoil up to 800m inland was removed (EN). 
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Earthquakes across the development scale.

  • Haiti earthquake - developing:
  • 12th Janruary 2010, a magnitude 7 that killed 230,000 and left 2.3 million displaced. 
  • 100,000 buildings damaged and rendered unusable.
  • 1 million live in squalid, tented camps and 1 million live in Port-au-Prince slums. 
  • Many small businesses destroyed due to unenforced building codes leading to less resistant buildings. 
  • Cholera endemic, corrupt government + densely populated areas. 
  • Sichuan earthquake - emerging:
  • May 2008, magnitude 7.9 that killed or left missing 87,150 people.
  • 4.8 million left homeless and 10 million need sheltering due to 7.5 million homes destroyed.
  • $191,913 million + 4.8 million homeless due to poor infastructure e.g. mudbrick housing and vulnerable school buildings. 
  • Japan earthquake - developed:
  • 11th March 2011, 9.1 magnitude killed 15,891 with 163,000 left needing shelter.
  • 12 mile evacuation zone for nuclear meltdown. 46,000 buildings destroyed. 
  • £250 billion damage, limited by well developed disaster plans and effective response. 
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Hazard profile case study

  • Phillippines earthquake:
  • 6.1 magnitude - rapid onset. 
  • Convergent plate boundary.
  • 27 seconds duration - 18km areal extent.
  • Predictable - High frequency.
  • Iceland earthquake:
  • 6.3 magnitude - relatively slow.
  • Divergent plate boundary.
  • 14 seconds duration - 10km areal extent.
  • Predictable - High frequency. 
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The risky-poverty nexus

-low income households and communities are often the hardest hit and suffer disproportionately from disaster impacts and losses. 

-Haiti 2010 death toll was estimated at 160,000 compared to Chile 2010 550, where vulnerability was exacerbated by inequality. 

 -Asset inequality - housing tenure, agricultural productivity(in farming communities) or goods and savings in trading communities. Low income households are forced into hazard-exposed areas due to cheap land where places have poor infastructure and social protection. 

  • -Inequality of entitlements - unequal access to public services and welfare systems and ineqaulities in application of law. 
  • -Social status inequality - to do with living space and ability of individuals to secure regular income and access to public services. 
  • Lack of secure tenure discourages investment into housing, services and measures.

-Political inequality - unequal access to political acquisition or resources. Little political 'voice' , often being exluded or marginalised. 

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Development, disaster impact and vulnerability

Elements of development that relate to vulnerability and disaster risk:

-creation of wealth and improvements in quality of life need to be equitably distributed. 

Development that creates inequality promotes social isolation and political exclusion. This can lead to groups residing in areas with poor infastructure and high enironmental degredation that makes them vulnerable during a hazard e.g. diseases through unsafe drinking water and unsecure dwellings. 

-health, education, housing and employment opportunities. 

-care and maintence of resource useage and distribution. 

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