Geologically and geodetically constrained slip rates: Implications for earthquake cycle dynamics and slip partitioning (Invited)

Rates of deformation at plate boundary zones are most commonly quantified using fault slip rates. Geologic fault slip rate estimates are constrained by dated offset marker units while geodetic fault slip rate estimates are based on model based inferences from interseismic velocity gradients. We present a new compilation of geologic and geodetic slip rate estimates for 17 continental strike-slip faults for which at least two geodetic and geologic fault slip rate estimates are available. While select faults (Garlock in southern California, Telas Ferghana in the Tien Shan) show marked discrepancies between these two types of slip rate estimates the best fit line describing the relationship between the two data sets is 0.85 +/- 0.08, with geodetic rates tending to slightly underestimate geologic rates. This remarkable agreement has implications for both the dynamics of the earthquake cycle and the understanding the nature of slip partitioning at continental plate boundaries. Visco-elastic earthquake cycle models predict time variable surface velocities that should affect geodetic slip rate estimates constrained using classical elastic half-space models. We show that the scatter between geologic and geodetic slip rate estimates is consistent with the predictions from earthquake cycle models with an upper mantle Burgers rheology but not the widely used Maxwell rheology which predicts significantly more scatter than is observed. Further, the fact that geodetic fault slip rate estimates do not systematically overestimate geologic fault slip rates suggests that the role of small faults near these particular structures may be kinematically negligible.