The average time interval between occurrences of a geologic event, such as a flood or earthquake, of a given or greater magnitude.

Determined from historical records. The average length of time between two events (rain, flooding) of the same size or larger. Recurrence intervals are associated with a probability. (For example, a 25-year flood would have a 4% probability of happening in any given year.)

Average period of time between two episodic events such as earthquakes, floods or volcanic eruptions.

Time interval in which an event can be expected to occur once on the average.

The average amount of time between events of a given magnitude. For example, there is a 1% chance that a 100-year flood will occur in any given year.

the average period of time between earthquakes in a seismic region.

The average interval of time within which the magnitude of a given event, such as a flood, will be equaled or exceeded one time.

The average time span between large earthquakes at a particular site. Also termed "return period".

The average time between runoff events that have a certain flow rate, e.g. a flow of 2 m/s might have a recurrence interval of two years in a particular catchment.

The time between hazard events of similar size in a given location. It is based on the probability that the given event will be equaled or exceeded in any given year.

The approximate length of time between earthquakes in a specific seismically active area.

Expected time interval between hydrologic events of a given magnitude (e.g., 100-year peak flow, 10-year/7-day low flow).

The average time between successive geologic events.