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Factors Affecting Hazard Risk

The risk posed by a hazard is affected by many things.  Not all earthquakes have the same impact the world over for example, and not all tropical storms are deadly.  Why is it that earthquakes of the same magnitude have different death tolls?  Why is it that hurricanes of the same magnitude create different amounts of economic damage? Some places are more VULNERABLE to natural hazards and some places have a lower CAPACITY TO COPE as they have weaker infrastructure, poor government organisations and agencies (such as the army, or police) or low quality equipment.

The major things affecting all natural hazards are;
1. Natural factors - things like rock type (geology) in an earthquake, the shape of a coastline in a tsunami, the height of the land hit by a tsunami can influence the effects.  For example, a gently sloping coastline will often suffer more damage than a steep coastline in a hurricane’s storm surge. It is known that generally earthquake shaking in soft sediments is larger and longer than when compared with the shaking experienced at a "hard rock" site. Softer sediments are more likely to liquefy too, which can contribute to building collapse.

Geological impact on earthquake waves

2. Magnitude - the size of the event massively affects the impact it has.  A hurricane of magnitude 5 on the Saffir Simpson scale will have more impact than that which has a magnitude 3, whilst every step up the Earthquake Richter scale represents a 10 fold increase in damage and a 30 fold increase in energy released.

Mercalli and Richter Scales
The Richter and Mercalli Scales - Image copyright Rob Gamesby

3. Frequency – this is how often the hazard occurs.  The more often a hazard occurs generally the more prepared people are, and the more used to coping they are.  Large earthquakes and volcanic eruptions are generally very rare events in terms of a human lifespan so when they occur they can surprise.  Floods are often regular events, large parts of Bangladesh flood every year for example.  In this event people can adjust their buildings and lives to cope with the risk associated.
4. Population density and distribution – this is the number of people in an area and where they are. Generally, the greater the number of people in an area, the greater the potential for disaster.  Therefore, an earthquake in Alaska will have less impact than one which hits a more densely populated area such as San Francisco. The Pacific Ring of fire covers a 40,000km horseshoe shape and has around 90% of the world’s earthquakes and 452 volcanoes. Hundreds of millions of people live in this zone, including over 20 million people close to Popocatépetl volcano in Mexico.
5. Level of development of the place - this determines how much money is available to PREPARE for the event in advance in terms of predicting the hazard and PREPARING people to cope with it, and also determines how the country RESPONDS after the event, wealthy places tend to respond quicker. High Income Countries (HIC) are generally much better at preparing and responding to natural hazards because;
Governments – their governments are often stable and democratic and have lots of agencies that can help during an emergency.  Being democratic means that the public can put pressure on the government to have life safe buildings that survive natural disasters, or makes then want to respond quickly as it will help get the politicians votes.
Technology – HICs can afford the technology to help them predict events, the USA has the United States Geological Survey to collect earthquake data from seismometers for example.  They also have the technology to help buildings survive various natural hazards
Planning laws – many HICs have laws that prevent building in hazardous locations, along a low coastline at risk from storm surges in a hurricane for example.
Agencies – many HICs have agencies that can act quickly to help people after a disaster, such as a well-equipped army or fire service and experts to coordinate a response in both the short and long term.

6. Management – the 3Ps (Predict, Prepare and Prevent)
Predict – some natural hazards are easier to predict than others, hurricanes can be identified by satellites and then tracked.  This allows governments to evacuate if needed.
Preparations - if a place is well prepared regardless of its level of development this can limit the impact of a hazardous event.  In India, despite its low level of economic development, rounded wooden houses have been designed to be earthquake proof, thus limiting the impact of these hazards.
Prevent – this could be preventing damage to buildings etc. through strict building rules.

7. Education – regardless of level of development people can be educated to survive natural hazards.  Education about the risks of contaminated flood water or Earthquake drills (like the ones Japan has on the 1st September to commemorate the 1923 Tokyo Earthquake) can save many lives.

Drop, Cover, Hold


8. Time - the amount of time since the last hazardous event can influence the impact, if a long time goes by people can be unprepared.  Also, if the hazard occurs when lots of people are asleep they can also be unprepared. The Christchurch Earthquake of 2011 happened during the day when lots of people were at work, this contributed to the death toll as many got trapped in collapsed office buildings.



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