Earthquake Recurrence Intervals on the San Andreas Fault

Possible recurrence intervals between earthquakes of different magnitude that may be generated along the San Andreas fault are derived by relating long-term offset rates since mid-Tertiary time, displacements, and lengths of breaks recorded for historic earthquakes, and tectonic creep rates.

The recurrence interval for earthquakes of different magnitude at a given point on the fault is believed to follow the relation:

where:

R_x

recurrence interval at a point on the fault,

D

displacement accompanying an earthquake of given magnitude (related empirically to Richter magnitude),

S

long-term strain rate (from offset of geologic units),

C

tectonic creep rate.

The recurrence interval for earthquakes of different magnitudes for the total length of the fault is then derived by weighting equation (1) according to the number of break lengths in the total length as follows:

where:

R_t

recurrence interval for entire fault,

L

length of break (related empirically to Richter magnitude),

L_t

total length of fault.

Tectonic creep is believed to be related to Richter magnitude, for example, small for segments of the fault characterized by earthquakes of large magnitude, and large for segments characterized by small earthquakes; and equations (1) and (2) can be weighted according to this relationship.