1 - Tectonic processes and hazards (Vulnerability, risk, resilience and…
1 - Tectonic processes and hazards
The global distribution of tectonic hazards
Main zones occur along
, earthquakes can be
Significant number located in the '
Ring of Fire
' around the Pacific Ocean.
near plate boundaries
but there are also
volcanoes; found in the
middle of tectonic plates
and are thought to be fed from the
underwater shock waves
from earthquakes or eruptions.
Most commonly experienced around the Pacific Ocean coastlines.
gently sloping continental shelf
allows them to build
Two different types of plates...
Thin crust underlying the ocean basins.
Thicker crust underlying the continents.
The low density of the thick continental crust allows it to 'float' on the much higher-density mantle below. Heat derived from the Earth's molten core rises within the mantle to create convection currents which, in turn, move the tectonic plates.
As the plates move relative to each other, they cause...
Continents to drift apart.
Ocean basins to change in size and form.
Formation of major landforms such as mountain chains and mid-ocean ridges.
Earthquakes, volcanic eruptions and tsunamis.
Important elements in the theory of plate tectonics...
The nature of the Earth's structure with a relatively thin crust broken up into plates and wrapped around a thick and largely molten mantle.
Convection within the mantle causes crustal plates to move.
4 different types of plate boundary are recognised.
New crust is formed by sea-floor spreading at divergent boundaries.
Crust is being destroyed and remoulded in subduction zones at convergent boundaries.
Slab pull is the force created by convection currents that moves plates and drags them into subduction zones.
Paleomagnetism provides evidence of plate movements.
The type and magnitude of event
The type of tectonic event is determenined by the type of plate boundary.
boundary = most productive of both
, followed by the
zone - boundary between an oceanic plate that is undergoing subduction and an overriding continental plate.
Physical processes behind tectonic hazards
in the Earth's crust. Outcome of a
and its sudden release. There are
three types of vibration
, or seismic waves produced:
point of origin within the Earth's crust
where the pressure is released.
- point on Earth's surface
directly above the hypocentre.
The S and L waves are more destructive than P waves. They cause crustal fracturing, ground shaking and three secondary hazards...
where slopes are weakened by seismic waves and slide under the influence of gravity.
: affects loose rocks and sediment. Sesismic waves trigger the ground to lose its load-bearing capacity, causing large buildings to settle int o the ground, tilt and possibly collapse.
depends on physical and human factors
Wave amplitude and distance travelled.
Depth and gradient of the offshore zone.
Degree of coastal protection by mangroves and coral reefs.
Quality of early-warning systems.
As they approach a coastline and the sea becomes shallower, the waves grow in heiight.
- frothing of magma produces bubbles that burst explosively to eject hot and poisonous gases as well as hot, fine materials.
Tephra (ash falls)
- rock fragments ejected into the atmosphere and ranging in sizes from 'bombs' to fine dust. The accumulation of it on roofs starts fires and causes buildings to collapse.
- mixed gases emitted during explosive eruptions. Carbon dioxide in it is particularly dangerous.
created by the
combination of heavy rain
on slopes covered by fine volcanic material.
caused by volcanic eruptions
Vulnerability, risk, resilience and disaster
- the ability of a community to cope with the impacts of a hazard.
Determined by a range of factors
including warning system quality, emergency response, development level and more.
exposure of people
to a hazardous event. Related to the probability of a hazard leading to a
loss of life
Hazard risk formula
involves the components that influence the
amount of risk a community
is taking with a particular type of hazard...
Risk = Hazard x exposure x vulnerability / manageability
pressure and release (PAR)
model sees disaster as occurring at the
intersection of two processes
those generating vulnerability and those of the natural hazard event.
ability of a community
or country exposed to hazards to
from the impacts of a hazard. It can
often help prevent a hazard from becoming a disaster.
The economic and social impacts of tectonic hazards vary considerably: over time; from place to place; from minor nuisances to major disasters.
of a tectonic hazard are
roughly proportional to the land area exposed
to the particular hazard. There are
other factors involved
, such as...
Level of development and per capita GDP.
Total number of people affected.
Speed of recovery (resilience)
Degree of urbanisation.
Amount of uninsured homes.
Tectonic hazard profiles
Magnitude and intensity
There are important aspects of tectonic hazards. Observations and measurements are converted to mathematical scales.
Follow the link for a table of scales used for two different types of hazard
They are useful as they can be completed and used to be
compared with the profiles of other events.
A hazard profile isn't the only factor that determines the social and economic impacts of an event.
The importance of development and governance
Economic development gives communities and countries
to the resources, organisations and technology needed to
cope with hazard events.
means people are better able to
ensure their own safety
by living in 'safe' locations and in 'hazard-proofed' property.
There are non-economic aspects of development that are significant...
Access to education
: education - more aware of hazard risks of living in locations and what to do.
Access to healthcare
: better health = better chance of withstanding health and food risks.
: bad quality housing = unable to withstand earthquake shock waves = serious injury/death.
: failing to invest in infrastructure, being ill-prepared to deal with the emergency situation following a hazard.
- higher density = more people at risk.
- more people and businesses concentrated in cities = higher risk and vulnerability.
Isolation and inaccessibility
- critical in the immediate aftermath where there is urgent need to provide emergency aid.
- strong spirit can help boost morale and the collective wish to survive.
Trends and patterns
All hazard data needs to be treated with some caution for a number of reasons...
no universally agreed
definition of a
in remote locations are
Disaster deaths and damage
Mega-disasters can distort trends in disaster losses.
Mega-disasters are large-scale in terms of the area involved and the impacts. They impose huge challenges and usually require substantial amounts of international disaster aid.
Hazard hotspots - locations are extremely disaster prone for a number of reasons. Noteable is the fact that they experience more than one type of natural hazard.
difficult to predict
although it is beginning to look like there
may be some early warning signs.
Hazard management cycle
Involves a number of stages once the hazard has struck...
Initial recovery (rehabilitation).
Reconstruction (including mitigation). Mitigation - action taken to reduce or eliminate the long-term risk to human life and property from natural hazards.
Return to normality.
Appraisal of the lessons learned during the event and implementations of remedial actions.
Improving preparedness (educating people about what they should do, improving warning systems and training, equipping rescue teams).
Follow the link to the diagram of the range of factors affecting the response to hazards
Park's disaster response curve
It is a model that can be used to help analuse the timeline between when a hazard strikes and when a place or community returns to normal life.
It recognises five stages which are a near match with the stages in the hazard management cycle.
Follow the link to see Park's model: the disaster response curve.
Mitigation and adaptation strategies
Three basic actions that can be undertaken to mitigate the impacts of a tectonic hazard...
Modify both vulnerability and resilience.
Improving prediction, forecasting and warning systems.
Improving community preparedness.
Changing behaviours that reduce the hazard risk.
Modify the potential financial losses.
Main way is through insurance. It is expensive but in most instances the actual costs of repair and reconstruction will be significantly more. The insurance has to assess:
Level of risk.
Probability of a hazrd of a certain magnitude happening.
Market value of the properties to be insured.
The likely costs of repair or reconstruction.
Modify the hazard event.
are yet capable of
preventing tectonic disturbances.
Mention might be made of:
strengthening coastal defences against tsunamis; diverting or chilling lava flows; increasing slope stability where there is high risk of landslides.