Targeting mitigation where it has most effect

The understanding of how the occurrence of a natural hazard or an accident turns into a disaster enables us to forecast likely situations where disasters are possible. If there were no human settlements or economic activities affected, an earthquake would be a harmless act of nature. The combination of settlements (elements) and earthquake (hazard) makes the disaster possible. Some elements are more vulnerable to earthquake effects than others. Identifying which these are - the elements most at risk - indicates priorities for mitigation.

Disasters are often the result of combinations of factors occurring together: a fire source, a dense residential area and combustible houses for example, or a seismic fault rupturing close to a city formed of high occupancy weak buildings. The contributory factors of past disasters can be identified to highlight similar conditions elsewhere. This is the process of risk analysis.

Identifying situations where combinations of risk factors coincide indicates the elements most at risk. The elements most at risk are the buildings, community services, infrastructure and activities that will suffer most from the effects of the hazard or will be least able to recover after the event. At a regional level, the concentrations of population and infrastructure in large cities make it likely that the losses inflicted by even low levels of hazard will exceed the total losses inflicted by severe levels of hazard on all the villages in the region. Mitigation measures in the city may have the most effect in reducing future losses. The portions of the housing stock in the city most likely to be damaged can be identified and mitigation measures applied to that sector will have the most effect on reducing risk. The number of elements likely to be affected by a hazard, together with their vulnerability to the hazard will identify where mitigation is most effective.