A Kinematic Model of Quaternary Fault Slip Rates and Distributed Deformation at the New Zealand Plate Boundary

We construct a kinematic model of Quaternary long-term deformation at the New Zealand plate boundary, including slip rates on major faults and strain rates between faults. We use an iterative method based on statistical and physical principles to find a velocity field that fits fault slip rate observations, has consistent off-fault strain-rate style, and is constrained by known plate motion. The kinematic model balances on-fault and off-fault deformation and provides improved estimates of fault slip rates and uncertainties in a statistically rigorous manner. We predict shortening rates of 45 +/- 8, 34 +/- 3, and 20 +/- 3 mm/yr across the northern, central, and southern portions of the Hikurangi subduction margin, respectively; these rates are lower and better constrained by regional kinematics than previous estimates. In addition, the model predicts large strains adjacent to the Alpine Fault, indicating similar to 9 mm/yr of plate motion in central South Island on faults with currently unknown slip rates. Differences between our long-term velocity field and a contemporary velocity field arise mainly through interseismic locking on major faults. However, we suggest that differences with contemporary deformation in northeastern North Island are due to uncertainty in Havre Trough extension parameters and < 5-10 mm/yr of missing dextral slip on unknown onshore faults, which implies seismic hazard is under-predicted in that region.