Tectonics theory

Factors affecting death toll

Wealth: afford solid infrastructure, quick response & health care units

Education: citizens know how to respond and the correct actions to take in an emergency

Population density: quantity of people affected in one area

Experience: An area prone to disaster knows what to expect and how to respond, could also lead to negative effects e.g if a developing country is hit by an earthquake and then once more- no time to recover

Location: if it is in an area where there is a high population density such as a city or shanty town

Contacts: whether the government has a good response team with contacts with other countries for aid and support.

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Degg's disaster model

= interaction of human and physical circles

Occurs when population can't:- Anticipate (before) e.g predict with tech

                                                 - Cope with (during) e.g secure buildings, evacuate

                                - Recover from (after) e.g organise emergency response, recover roads etc

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Movement of tectonic plates

Mantle Convection:  Radioactive decay of inner core produces heat= mantle rises                                          & CC form- NOT UNIVERSALLY ACCEPTED TODAY

Slab pull: Oceanic plate forms at mid-ocean ridges, plates diverge & cool:

                    -become denser= sink/subduct into asthenosphere excerting force

                      & pulling plate/itself behind                 

Seafloor spreading (ridge push): magma rises between diverging plates & erupts as                                                            lava = forms mid-ocean ridge

                                                 Oceanic plates pushed apart by force of mid-ocean ridge

THESE ALL COMBINE- convection currents drive plates, lava rises = ridge push, old plates subduct= slab pull

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Earth's structure

(I) Inner core =solid

(Once) Outer core = molten & hot due to radioactive decay (4000-6000C)

(Made) Mantle =semi-molten & plastic so can flow, 2300km thick

(A ) Asthenosphere = semi-molten plastic layer of upper mantle

(Massive) Moho = (the mohorovicic discontinuity)

(Lemon) Lithosphere =crust & solid uppermost mantle (which has cooled & stuck to crust), thin, cool & rigid = broken into tectonic plates                               

(Cake) Crust

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Continental vs Oceanic

               Continental                                                      Oceanic

·     Solid rock = form continents                                 Solid rock= form ocean floors

Can extend out to sea to form underwater continental shelf      Covers 65% of Earth’s surface

Relatively thick- 70km from peak to depth in mountains  Relatively thin- 6km

Low density-60% silica content                    High density- composed of Basalt

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Plate tectonics theory

= describes movement of Earth’s tectonic plates & builds on earlier discoveries of

-continental drift (Pangea & continental puzzle)

- Seafloor Spreading

- Earth’s structure

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Destructive plate boundaries

=Convergence of two plates; where subduction= high risk cone volcanoes & viscous lava

O & C: Oceanic plate subducts & melts due to heat and friction from mantle

           Magma rises through faults in continental plate & erupts as lava to form chain of                          volcanoes

          Continental plate crumple upwards to give fold  mountains &also volcanoes= The Andes

O & O: Denser/older plate subducts

             Magma erupts to form submarine volcanoes and an island chain= The                                              Antilles

C& C: Collision, plate margins & sediments crumple to give fold                                                                mountains=the Himalayas

All = High risk Earthquakes: shallow, intermediate & deep due to friction in Benioff Zone, magnitudes high and focus potentially shallow

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= provides evidence for divergence of plates

Rocks formed at different times in history have their magnetic minerals lined up in different directions- when erupting lava cools the magnetic minerals lock in Earth’s polarity at the time. At mid-ocean ridges the same patterns of magnetic direction stretched away from each other indicating the matchings rocks on either side of the ridge had formed at the same time and then diverged.

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Constructive plate boundaries

Diverging margins usually  between two oceanic plates

Ø  Low risk (non-viscous lava) shield volcanoes mainly on ocean floor= Mid-Atlantic ridge

Ø  Little friction= low risk earthquakes of low magnitude & shallow focus

Ø  When between two continental plates= volcanoes and rift valleys e.g East African rift valley

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Conservative plate boundaries

Two plates sliding past each other

Ø  Movement along boundary

Ø  Mostly oceanic-oceanic but can be continental-continental e.g San Andreas Fault

= no volcanoes as no subduction or divergence

= High risk earthquakes at continental as magnitudes are high and focus shallow due to friction

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Predicting volcanoes- methods

Seismic Activity

Ground deformation

Thermal Changes

Gas emissions

Rising magma triggers seismic activity- measured with seismometers & is usually first indication of ‘volcanic unrest’

Type & intensity of seismic activity= when eruption likely to occur

Rising magma changes shape of volcano due to heat and pressurisation.

Tiltmeters, strainmeters, GPS and satellite images used to measure even smallest swellings.

Rising magma heats crust- infra-red satellite images= thermal mapping to detect any warming of crust.

These can be done remotely reducing risk and making process less time consuming & allows measurement of hard to reach areas.

Gases escape from magma as it rises- correlation spectrometers measure gas concentrations.

Sudden rise= pressure building in volcano which may lead to violent eruption

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Predicting volcanoes- drawbacks

= mostly only available in developed world but can still go wrong.

e.g Japan 2014, despite complex monitoring systems Mount Ontake erupted without warning killing 47 unsuspecting people.

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Measuring earthquakes- Moment magnitude scale

Moment Magnitude Scale:

= total energy released at epicentre at seismic moment.

Includes: size of seismic waves, amount of slippage, area of fault affected

Scale starts at 1 but is infinite and is logarithmic e.g Japan 2011 earthwuale = 9.0 and released 1000x more energy than Haiti 2010- 7.0.

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Measuring Earthquakes- Modified Mercalli Scale

= Uses witness observations (subjective)

Includes: impacts on natural environment, people, and structures

Scale ranges from I (hardly noticed) to XII (catastrophic)

Image result for modified mercalli scale table

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Types of lava

Basaltic Lava

Andesitic Lava

constructive boundaries & hot spots

Destructive subductive boundaries

Low viscosity = runny

High viscosity = sticky

Gases escape freely

Gases trapped in magma and explode out

Effusive = gentle

Explosive= violent

Low risk & frequent

High risk & infrequent

Eruptions usually VEI 0-3

e.g Kilauea Hawaii, VEI=  0

Eruptions usually VEI 4+

e.g Mt Pinatubo Philippines, VEI=6

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= Volcanic Explosivity Index, measuring eruption magnitude

Includes: amount & height of erupted material, duration of eruption, description (e.g violent/effusive)

Scale ranges from 0-8 non-explosive to extremely explosive = logarithmic

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Seismic waves- P waves/ Primary/Pressure waves

Ø   Travel from focus

Ø  Push through Crust, Mantle & Core

Ø  Backwards and Forwards motion

Ø  Only damaging in powerful EQ’s

Ø  Body waves

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Seismic waves- S waves/ Secondary/Shear waves

Ø  Travel from focus

Ø  Shake through Crust & mantle

Ø  Sideways motion at right angles to direction of travel

Ø  Body waves

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Seismic waves- L waves/Love waves/ Surface waves

Ø  Travel from epicentre NOT focus

Ø  Shake along ground surface only

Ø  Sideways motion at right angles to direction of travel

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Seismic waves

= energy released from earthquake

  • P waves          Speed decreases
  • S waves          Damage increases as amplitude becomes
  • L waves           greater

All measured using Seismometer= detects & measures ground movement, recording it on seismograph.

Using speeds of different waves Scientists can calculate time, location & magnitude of EQ.

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Cause of a tsunami

  • Seafloor uplifted/displaces by EQ/slipping tectonic plates/tectonic event
  •  Water column directly above & thus ocean surface= displaced, waves radiate in all directions
  • Difficult to detect in open water as waves are shallow (0.5-5m) and wave length is long (150-250km)
  • Wave energy concentrated into smaller vol. near coast
  • Water shallows= waves increase in height 1m waves--->30m waves
  • Wave’s crest reaches shore= vacuum & sea floor exposed
  • Water returns and floods inland

= soil washed away, trees uprooted, people & infrastructure swept away, land food & water= contaminated by salt sewage & bodies= disease e.g cholera, drowning collapsed buildings & floating debris= death

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Predicting tsunamis

DART= Deep-ocean Assessment and Reporting of Tsunami

Uses: seafloor sensors & surface buoys= monitor changes in water pressure and sea level

When tsunami waves are detected, signals are sent via satellite to warning stations, data can then be used to predict size and direction of tsunami.

= gives people chance to evacuate and for emergency procedures to be put into place

BUT not completely reliable… Japan 2011 size of tsunami underestimated, and some didn’t evacuate, despite Japan having most extensive tsunami warning system globally.

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The Hazard-Risk Equation

Risk= Hazard x Vulnerability/Capacity to cope

Human factors affect vulnerability/Resilience of country- developing countries + vulnerable to natural disasters than developed.

Physical & environmental Factors

Economic & Social factors

Governance & Politics

High pop. Density= increased low quality housing

Few jobs= no money to prepare/cope with hazard

Level of corruption= resource utilisation

Rapid urbanisation= quick, poor quality housing

Poor health care= less likely to recover from hazard

Existence of Hazard education & practise responses

Accessibility of area for emergency services and supplies

Level of wealth= quality of housing & ability to cope

Quality of communication systems


Lack of education= unaware of risks

Efficiency of emergency services



Quality of infrastructure & building codes and regulations

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Pressure and Release model

= identifies causes of vulnerability

 Root causes             dynamic pressures             unsafe conditions = cycle of effects

E.g poverty              lack of skills            poor quality housing = progression of vulnerability

The pressure and release model  

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Hazard Management theory

Aims: Ø  Limit life & property (before)

 Ø  Help those affected (during)

 Ø  Ensure rapid recovery (after)


Ø  Government (local, regional & national)

Ø  IGO’s

Ø  Businesses

Ø  Community groups

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Hazard Management cycle

Image result for Hazard management cycle

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Hazard management cycle- explained


  • Occurs before & after events
  • = identifying potential hazards and reducing their impact


  • Occurs before event 
  • = prep for response to and recovery  from event


  • Occurs during/immediately after event
  • = coping with hazard event


  • Occurs after event
  • =short-term recovery, meeting immediate needs
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Disaster trends

Total no. of disasters reported dramatically risen= better tech e.g monitoring & recording events.

Amount killed globally by disasters= falling

  •   Better early warning systems
  • Improved building codes & disaster preparedness
  • Overall cost of disasters rising from $20bill/yr to $100bill/yr between 2000-2010

Data usually incomplete as:

  • when disaster strikes immediate effort= rescue NOT data collection
  • no single organisation responsible, methods vary
  • Differences in definition and key terms/categories used= misunderstandings
  • Difficult to gather data from remote areas, under-reporting of death (places that require help and data)
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Hazard profiles

= diagram that shows main characteristics of tectonic events- help governments and other organisations to develop effective management strategies.

Potential profile factors:

Magnitude/ Speed of onset/ Duration/ Areal extent/ Spatial predictability/ Frequency

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Hazard profiles- examples

Indian Ocean tsunami

  • High magnitude
  •  Rapid onset
  • Widespread extent

= organisations focus on making sure early warning systems are at reach in all countries that might be affected


  • Small
  • Slow
  • Limited extent, predictable & common

= government focus on developing evacuation plans 

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Park-Hazard Response Curve

= theoretical model showing how a city/country/region may respond after a natural disaster. Can be used to compare responses to different events or in different places.

Image result for park hazard response curve

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Park-Hazard Response Curve- explained

Stage 1= shows quality of life at normal eqm level

Stage 2= where hazard occurs

Stage 3= event has occurred, search & rescue underway. Quality of life drops at this stage and stays low for hours or days depending on severity and development of region.

Stage 4= relief strategies underway, takes variable amounts of time- hours, days, weeks or months to reach this stage, but quality of life is improving.

Stage 5= long-term human response, rebuilding and restoring normality. Quality of life returns to normal, in some cases it can be higher than it was originally with repairs of old infrastructures. However, in some cases such as Haiti it does not return completely to normal.

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