Tectonics

Tectonics

1. plate boundaries

   • types
     • divergent/constructive
       • rifts, new crust, volcanoes
     • collision
       • mountains
     • conservative
       • sliding opposite ways, earthquakes
     • convergent/destructive
       • subduction zone, mountains, volcanoes
   • subduction zone:
     • 2 plates moving together, ocean subducted under continent
       • fold mountains created & volcanoes & earthquakes

2. Earthquakes

   • normally along plate boundaries, often convergent & conservative
   • sudden movements, near surface, pre-exisitng faults.
   • gradual pressure buildup released.
     • vibrations (waves)
       • L waves (love waves) : surface - horizontal on surface
       • S waves: slow - only solids
       • P waves: fast - solid & liquids
       • severity of earthquake based on amplitude.
       • S & L waves most destructive. crustal fracturing & 3 secondary hazards.
         • Liquefaction
           • loose rocks & sediment affected. ground looses load bearing capacity.Large buildings settle in the ground / collapse
             • (turns ground into liquid)
         • Tsunamis
           • earthquakes out to see/secondary impact.
         • Landslides
           • slopes weakened by seismic waves. ground slides due to gravity
       • Rayleigh wave: surface of crust, rolling motion, responsible for most shaking felt by people.
   • hypocentre/focus
     • point where pressure is released
   • epicentre
     • on surface above hypocentre
   • Impacts
     • vary
       • over time
       • from place to place
       • nuisance to disaster
     • usually far worse than volcanoes
     • 5% of population likely to be affected
     • factors
       • speed of recovery (resilience)
       • total number affected
       • level of development & per capita GDP
       • amount of uninsured losses
       • level of urbanisation

3. volcanoes

   • around 500 active now.
     • a lot in the ring of fire
   • near plate boundaries, also hotspots
     • hot spots: middle of plates, fedfrom underlying magma, area of thin crust
       • e.g. Hawaii
   • primary hazards:
     • pyroclastic flows
       • magma at the vent bubbles & burst, hot materials & poisonous gases roll down mountain sides
     • Tephra (ash falls)
       • rock fragments fired into atmosphere. sizes - boulders to dust. accumulate on roofs = building collapse, start fires.
     • lava flows
       • flows of molten rock, fast moving & lethal
     • volcanic gases
       • mixed gases released in explosion. CO2 very dangerous
   • secondary hazards:
     • lahars
       • mud flows, caused by heavy rain on slops & fine volcanic material
     • jokulhaups
       • floods caused by eruptions under glaciers.
   • impacts
     • only small area directly damaged
     • only 1% of world likely to suffer volcanic eruption
     • factors
       • level of development per capita GDP
       • number affected
       • speed of recovery (resilience)
       • amount of uninsured losses
       • level of urbanisation
   • lava types:
     • basaltic lava
       • 1000-1200 C, thin runny, gentle, ocean hot spots, mid ocean ridges, shield.
     • andesitic lava
       • 800-1000 C, slow, violent, moderately explosive, composite, subduction zones.
     • rhyolitic lava
       • 650-800 C, thick stiff, violent, super & composite volcanoes.

4. Tsunami

   • submarine shock waves
     • from earthquakes/volcanoes
   • often around pacific coast
     • gentle sloping shelf = great heights
   • most lethal secondary earthquake hazard.
   • no threat out to sea. only as land gets shallow they grow in height.
   • impact depends on:
     • event duration
     • wave amplitude & distance travelled
     • depth & gradient of offshore zone
     • coastal barriers
       • mangroves
       • headlands
       • reefs.
       • sand banks
       • Cliffs
     • day/night
     • warning systems
     • population density/ degree of developments on coast.
   • impacts
     • factors
       • level of development per capita GDP
       • numbers affected
       • speed of recovery (resilience)
       • amount of uninsured losses
       • level of urbanisation

5. theory: surface = 2 types of plates. thin crust underlying ocean & thick underlying continents. thick crust floats (less dense)

   • crust formed at divergent boundaries on sea floor
   • convection currents = movement

6. paleomagnetism

   • magma locking in earth's magnetic polarity, used to reconstruct plate movement

7. Hazards: natural events that threatens/causes injury & deaths, damage to property

8. Disasters: occur when hazards have significant impact on populations. hazard becomes disaster when 100+ die/affect.

   • Risk = (hazard x exposure x vulnerability) / manageability

9. Risk: exposure of people to hazards. relates to probability of a hazard leading to loss of life/lively hood.

   • difficult to assess, can include:
     • individual/community perception
     • unpredictability of hazard.
       • people get caught out by timing/magnitude.
     • lack of alternatives.
       • people still live in hazard zones, lack of options, good farming
     • benefits of living in area can out weigh negatives
     • acceptance of risk

10. Vulnerability: how likely a community/structure is to suffer from a disaster.

11. resilience: ability for community to resist, absor & recover from a hazard.

12. Hazard Profiles

    • magnitude & intensity
      • richter scale
        • earthquake
        • 0-9
        • measures height of waves, absolute scale, will measure the same anywhere. 1 on scale = 10X
      • Mercalli scale
        • earthquake
        • I-XII
        • different amounts of shaking, based on damage & movement of goods
      • Moment magnitude scale
        • earthquake
        • 0-9
        • describes earthquake in terms of energy released. based on seismic movement, calculated by amount of slip in the fault. used by US Geological Survey for large earthquakes. 1 on scale = 10X
      • volcanic explosivity index
        • volcanoes
        • 0-8
        • measured from volume of products ejected. increase in 1 on scale = 10X
    • hazard profiles used to compare
    • understand the physical characteristic of hazards
    • earthquakes, volcanoes, tsunamis

13. development & governance

    • often correlates to vulnerability & resilience
    • economic development
      • access to resources, organisations, technology
      • higher income leads to living in safe locations/hazard proof areas.
    • education access
      • aware of hazards/what to do
    • heathcare access
      • better health
      • resistance to disease
    • housing
      • poor quality
        • cant withstand hazards
    • governance
      • way a country, city, community, company etc is run
      • three concepts
        • authority
        • decision making
        • accountability
      • good governance embraces principles such as rule of law, transparency, equity, participation
      • poor governance can be corrupt, weak both increase vulnerability
        • failing to invest in infrastructure, warning systems
        • ill prepared
      • stakeholders: individuals, communities, organisations. governments, businesses with interest in situation (hazard risk)

14. geographical factors

    • population density
    • urbanisation: people, goods, businesses at risk
    • isolation/inaccessibility: hard to get help
    • community spirit: boost moral

15. contrasting locations

    • high development
      • an handle better but more financial damage
    • low development
      • rely on others, less to loose

16. management of the disasters & hazards

    • mega disaster
      • large scale (area involved & economic, human impact)
      • huge challenges, especially at emergency stage.
      • substantial international aid
    • no universal definition for disaster
    • small events in remote locations often under/not recorded
    • disaster, death, damage often under recorded for political reasons
    • some parts are at risk of multiple hazards, locations with 3 overlapping hazards = hazard hot spot
      • extremely disaster prone, more than one type of natural hazard
    • predicting
      • volcanoes have some signs
      • harder to predict earthquakes
        • need to detect areas of tectonic stress
    • management cycle
      • 3. reconstruction & mitigation
      • 2. initial recovery (rehab)
      • 1. emergency response
      • 5. lesson learned, implement remedial actions
      • 4. return to normal
      • improving preparedness
    • mitigation & preparedness
      • preparedness: educating people about what to do & improving warning system & equipment
      • mitigation: action taken to reduce/eliminate risk to life & property in future
        • often outcome of stage 5 and taken in stage 3
        • referred to as adaptation
      • 3 basic actions to mitigate the impacts
        • modifying the hazard event
          • no tech yet
          • strengthening coastal defences
            • tsunami
          • diverting/chilling lava flows
          • increasing slope stability
        • modifying vulnerability and resilience
          • improving prediction
            • forecasting prediction, warning systems,
              • scientific research, modern tech gives better warning systems.
          • improving community preparedness
            • enforcing building codes, especially public buildings.
          • changing behaviours, moving people away from high risk zone
        • modifying potential financial loss
          • insurance
            • insurance need to asses:
              • level of risk
              • probability of certain magnitude hazard
              • market value of property to be insured
              • likely cost of repair & reconstruction
          • Disaster aid
            • often during the emergency/early recovery
            • donations from
              • voluntary organisations & charities
                • e.g. Red Cross
              • governments to intergovernmental organisations
                • e.g. UN
            • often criticised as they can be inefficient or corrupt, does not encourage self help and bottom up management
    • response
      • factors affecting response
        • physical
          • type of hazard
          • topography of area
          • climate
          • accessability
        • human
          • scientific understanding
          • level of community preparedness
          • technology/engineering
          • population density/number involved
          • education & training
          • economic wealth
          • infrastructure
          • government framework
      • Parks response curve
        • used to analyse timeline between hazard striking and return to normality
    • Sendai Framework
      • 1. understand the disaster risk
      • 2. ensure government strengthening to manage hazard risk
      • 3. invest in improving resilience and disaster preparedness
      • 4. 'build back better' in recovery

17. earth structure

    • inner core
      • 7000 C
      • very dense
      • 80% iron 20% nickel
      • solid
    • mantle
      • 870 C
      • medium to less dense
      • upper = olivine lower = magnesium silicate
      • phases of solid and liquid
    • crust
      • 400 C
      • less dense
      • granite (continental) basalt (oceanic)
      • solid
    • outer core
      • 4400-6100 C
      • dense
      • 88% iron 12% sulphur
      • liquid