4. Natural hazards worldwide, risk management

4.1 Natural hazards

The notion of natural risk can be defined schematically by the equation :

Mathematically speaking, the risk associated with a particular hazard, in a given geographical area, can be defined as the mathematical expectation of damage due to the occurrence of the hazard in question over the reference period.

If the structure has been designed to withstand a particular intensity of a given hazard, the risk attached to the structure will be reduced by a certain amount. However,...