What this lesson teaches
I can explain why disaster risk from earthquakes and eruptions differs between places.
Syllabus K335, Topic 4.3, Key Question 2. Why do disaster risks related to earthquakes and volcanic eruptions vary across places?
Make a guess
In 2010, Chile had a far larger earthquake than Haiti, yet far fewer people died. What best explains this?
- Fewer people live in Chile than in Haiti.
- Chile's buildings and preparation were stronger.
- Chile's earthquake was much smaller in size.
- Haiti is much closer to a plate boundary.
Show the answer
Chile's buildings and preparation were stronger.
Chile had strict building codes and experience of earthquakes. Haiti had many weak buildings and little preparation, so vulnerability made the difference.
The same earthquake can cause very different losses in two places, depending on shaking, ground, buildings and people.
Disaster risk is the possible harm when a hazard meets exposed and vulnerable people, property or ecosystems. Exposure means being within the hazard's reach. Vulnerability means being easily harmed and having limited ability to cope. Deaths, injuries and property damage are possible results, not certain ones.
The event itself matters. Longer shaking puts buildings through more cycles of stress, so it can cause more damage. The time of day changes where people are: at home, at school, at work or travelling. A night earthquake is not always worse; it depends on building quality, routines and emergency response.
Distance and ground matter. Shaking usually weakens with distance from the rupture, but depth, the path of the waves and the local ground change this. Soft sediment can make shaking stronger, and loose, waterlogged ground can liquefy. Solid rock usually shakes less. Distance from the epicentre helps, but geology gives a fuller explanation.
Buildings matter. Hazard-resistant design reduces the chance of collapse. Poor materials, weak joints, lack of maintenance and ignored building rules increase vulnerability. A building's height and shape also affect how it responds to shaking, so its material alone cannot tell you how it will perform.
Population matters. High density puts more people and buildings in the affected area and can strain rescue and services. Yet a well-planned dense city may have stronger buildings and better emergency services than a scattered village. Compare both how many people are exposed and how well they can withstand the event.
- Duration
- Longer shaking causes more damage.
- Ground
- Soft or wet ground can increase shaking.
- Buildings
- Good design and enforcement reduce collapse.
Step by step
The event
How long, when, how deep and how far away.
The place
Ground, buildings and population.
The response
Access, resources and working services.
Real examples to use
Haiti and Chile, 2010
Haiti's magnitude 7.0 earthquake killed over 220,000 people, while Chile's far larger magnitude 8.8 earthquake killed fewer than 800. Chile had strict building codes and experience of earthquakes; Haiti had many weak, poorly built buildings and little preparation.
Kobe, Japan, 1995
This magnitude 6.9 earthquake struck at 5.46 am, when many people were asleep in older wooden houses. More than 6,000 people died.
Worked example: Rules are not the same as action
Two towns have the same building rules. One inspects buildings and uses skilled builders. The other does not enforce the rules. The second town is more vulnerable, even with the same rules on paper.
Watch out for this
The nearest, most crowded town always has the biggest losses.
Distance and density matter, but ground, buildings and emergency services can change the outcome.
Check your understanding
Why can two equally strong earthquakes cause different building losses?
- Shaking time, ground, buildings and exposure differ.
- The magnitude decides collapse, so building quality hardly matters.
- Magnitude is worked out from the repair costs afterwards.
Show the answer
Shaking time, ground, buildings and exposure differ.
Yes. Many factors besides magnitude affect losses.