Displacement rates of normal faults

Abstract

Previous estimates of displacement rates on individual faults have been limited to neotectonic faults and averaged over time intervals of about 200 kyr or less1,2,3,4,5. These estimates have been highly variable, which has led to a belief that longer-term displacement rates on individual faults are likely to be variable as well. Here we report estimates of long-term normal-fault displacement rates averaged over time intervals ranging from 1 to 40 Myr, and based on observed decreases in displacement of progressively younger horizons intersected by syn-sedimentary faults. We find that displacement rates are remarkably stable over 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 indicate that faults become large relative to nearby faults by having higher displacement rates, even when small, rather than as a consequence of having been active for longer. Our analyses also show that high regional strain rates tend to be accommodated by high fault displacement rates rather than high fault densities.