We develop a multi-segment M8.6 rupture model of a Hikurangi megathrust event, including unilateral rupture with propagation towards the northeast, in accordance with Schellart and Rawlinson (2012). We use the Graves and Pitarka hybrid Irikura method (Pitarka et al., 2018; GP-IM) for developing the source model. The maximum slip over the rupture planes is approximately 14 m, and the average slip is approximately 3.5 m. Both of these values are broadly consistent with the scaling relations developed by Tajima et al., (2013) and Skarlatoudis et al. (2016). In future work, we will develop additional rupture models and will perform simulations to assess the importance of slip randomness, asperity number and location, and hypocenter location on the synthetic ground motions.