Abstract - A recent model of fault growth suggests that many faults establish their lengths rapidly and for much of the duration of deformation grow principally by the accumulation of displacement. For faults consistent with this model we investigate the factors controlling displacement rates and average recurrence intervals using the lengths and displacement rates for 274 normal faults from 4 extensional regions. Our analysis of the evolution of fault systems on geological time scales (i.e. 60 kyr to 7 Myr) suggests a broad positive correlation between fault length and displacement rate for each region. Combining established earthquake-scaling laws with fault length and displacement rate data permits average recurrence intervals to be estimated. We conclude that earthquake recurrence intervals in a particular fault system are, to a first approximation, constant for a range of fault sizes. Therefore, larger faults generally have higher displacement rates than smaller faults because they accommodate larger earthquakes with greater coseismic slip. Stochastic and numerical modelling results suggest that fault interaction (and location) and intrabasinal strain rate variations are the principal factors responsible for scatter in the relations between length and displacement rate of individual fault systems; migration of the locus of faulting and death of large faults could be important in other areas. Further analysis indicates that decreases in recurrence intervals between fault systems arise principally due to increases in regional strain rates. A negative correlation between average recurrence interval and basinal strain rate is confirmed by independent estimates of recurrence intervals from paleoseismological studies, and supports the notion that the number of large active faults in a system remains approximately stable, with increased strain rates accommodated by greater fault displacement rates rather than by the introduction of more large active faults. Basin-wide strain rate and fault size are the primary controls on recurrence intervals, with fault interaction and intrabasinal strain rates being important secondary factors.
Abstract of talk given to:
AGU Annual Conference, San Francisco, December 2003.