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 This map has been superseded by Jennings, C.W., 1994, Fault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. |