DISPLACEMENT RATES OF NORMAL FAULTS

Previous estimates of displacement rates on individual faults have bee n limited to neotectonic faults and averaged over time intervals of ab out 200 kyr or less(1-5). These estimates have been highly variable, w hich has led to a belief that longer-term displacement rates on indivi dual faults are likely to be variable as well. Here we report estimate s of long-term normal-fault displacement rates averaged over time inte rvals ranging from 1 to 40 Myr, and based on observed decreases in dis placement of progressively younger horizons intersected by syn-sedimen tary faults. We find that displacement rates are remarkably stable ove r these longer time periods, and within a given fault system the rates are strongly dependent on the relative size of the fault (as measured by cumulative vertical displacement), Taken together, these results i ndicate that faults become large relative to nearby faults by having h igher displacement rates, even when small, rather than as a consequenc e of having been active for longer, Our analyses also show that high r egional strain rates tend to be accommodated by high fault displacemen t rates rather than high fault densities.