Recency of fault movement refers to the time period when the fault is believed to have last moved. The age is expressed in terms of the Geologic Time Scale. Generally, the older the activity on a fault, the less likely it is that the fault will produce an earthquake in the near future. For assessing earthquake hazard, usually only faults active in the Late Quaternary or more recently are considered. These include the following three non-overlapping time periods:

Historic: Refers to the period for which historical records are available (approximately the past 200 years in California and Nevada). Holocene: Refers to a period of time between the present and 10,000 years before present. Faults of this age are commonly considered active. For the purpose of classifying faults, C.W. Jennings* defined Holocene to exclude the Historic; that is, from 200 to 10,000 years before the present). More about the Holocene Late Quaternary: Refers to the time period between the present and approximately 700,000 years before the present. Here too, for the purpose of classifying faults, Jennings defined Late Quaternary to exclude the Holocene and the Historic. More about the Quaternary Unavailable: Refers to most faults in Nevada and a few in California which are not classified.

*"Preliminary Fault Activity Map of California" by C.W. Jennings (1992, California Division of Mines and Geology Open-File Report 92-03). This map has been superseded by Jennings, C.W., 1994, Fault activity map of California and adjacent areas, with locations and ages of recent volcanic eruptions: California Division of Mines and Geology, Geologic Data Map No. 6, map scale 1:750,000.