Although we are uncertain about how and when earthquakes will occur and the intensity of the associated ground-shaking, forecasts of the level of expected earthquake groundshaking are important to society for planning purposes. These forecasts are conveyed in probabilistic seismic hazard maps.
Probabilistic seismic hazard maps may be viewed as the earthquake analog to long-term weather forecasts. Most people accept that the weather cannot be predicted accurately and instead accept the idea of a forecast that states the likelihood of a climatic condition occurring during some time period. In the absence of abundant observations over the full range of climatic conditions, for example, from drought to flood, models of extremes in climate must be employed to estimate the probabilities of the hazardous conditions. Just as these probabilities can be used by society to prepare for extreme weather conditions, seismic hazard maps can be used to prepare for the damaging ground-shaking caused by earthquakes.