1.8 Concept of time and space

Probability- already discussed in 1.5.
For some hazards, e.g. landslides, specifying a time frame for the occurrence of a phenomenon is difficult to determine even in ideal conditions. As a result hazard is represented by susceptibility, which suggests areas potentially affected by landslides and does not imply a time frame when a landslide might occur.

Magnitude- simply, an expression of the power of a destructive event. Earthquakes- Richter scale, MMI scale, moment scale; Hurricanes- Saffir-Simpson scale.

Frequency- number of events of a given size in a given unit of time; number of events, and their sizes in each of a succession of time units; how often a given magnitude event occurs.

Return period or recurrence interval- is the average length of time between events of a given size; reciprocal of their frequency.

Magnitude-frequency Principle- states that the amount of work done by events of a given size is a product of their magnitude times their frequency of occurrence (Figure 7 and Figure 8).