Surface slip variability on strike-slip faults

Slip in strike-slip earthquakes is spatially variable along a fault, but the degree to which variability over short length scales is inherent to the rupture process or introduced by interpretation and measurement has not been quantified. In this study, we examine the effects of interpretation error on apparent short-wavelength variability in surface slip distributions by comparing numerical landscape evolution models and recent ruptures on strike-slip faults measured by hand and with image correlation. Surface slip distributions measured by hand from 63 strike-slip earthquakes have average spatial variability (CVslip-spatial = standard deviation/mean) of 0.43-0.52, and a total range of 0.14-1.14. Displacement measurements of offset geomorphic markers from numerical models that simulate constant slip along a fault have average spatial variability of similar to 0.25-0.40 when measured by hand and no spatial variability when measured by image correlation. Slip distributions from seven recent ruptures measured by image correlation have short-wavelength variability of 0.09-0.29, which is considered inherent to how rupture propagates to the surface. Our results demonstrate that variability innate to the rupture process and introduced by interpretation both contribute substantially to the observed variability in slip distributions measured by hand. Resolving the extent to which short-wavelength variability is inherent to rupture propagation through near-surface material versus an artifact of interpretation furthers understanding of the relationship between surface rupture and fault mechanics and informs interpretation of slip distribution and slip-per-event in past earthquakes.