HAZARD DETERMINES RISK, and WE HAVE CHOICES FOR MITIGATION
Geologic HAZARDS are mainly geologic processes that pose a temporary risk to people or buildings that happen to get in their way. The process will vary in severity (magnitude) through time, according to some frequency-magnitude relationship (e.g., large floods occur every 100 years, smaller floods every 2-5 years). Therefore, the essence of geologic HAZARD analysis is to figure out what the hazard is, where it is, and what its frequency-magnitude relationship is.
In contrast, RISK is the product of HAZARD times the VALUE of what's exposed to the hazard. If there is nothing of value exposed to the hazard (e.g, a rockfall in an uninhabited desert), there is no RISK. The HAZARD is still there, but there is nothing to "damage", so there is no RISK. Risk can be calculated this way on an annual basis (risk/year) or over longer periods such as the lifetime of a structure (50-100 years).
Defining hazard and risk in this way makes it easier to make a true estimate of RISK, and thus to design mitigation schemes that minimize RISK, rather than simply minimizing HAZARD.
GEO-HAZ suggests minimizing the risk from geologic hazards via one or more of these approaches:
- Avoid the hazard
- Mitigate the hazard at its source
- Mitigate what is at risk
- Accept the risk and insure against it