Displacement rates and average earthquake recurrence intervals on normal faults

The factors controlling fault displacement rates and average recurrence intervals are investigated using data for 274 faults from four extensional regions. Combining established earthquake scaling laws with fault length and displacement rate data permits estimation of average recurrence intervals for each of the regions. Broad positive correlations between fault length and displacement rate are attributed to the proportional scaling of earthquake slip and rupture length coupled with constant average recurrence intervals that are independent of fault length. 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 average 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 typical recurrence intervals from paleoseismological studies, and support the notion that high strain rates are accommodated by faster moving faults rather than larger numbers of faults. Basin-wide strain rate and fault size are the primary controls on displacement rates and average recurrence intervals, with fault interaction and intrabasinal strain rates being important secondary factors.