زلزله ی 2016 کاکورا: گسیختگی همزمان سطح مشترک فرورانشی و گسل های بزرگ The 2016 Kaikoura ¯ earthquake: Simultaneous rupture of the subduction interface and overlying faults

1. Introduction At 12:03 am local time, on November 14th, 2016, a moment magnitude (Mw) 7.8 (USGS) earthquake struck the Kaikoura ¯ region of South Island, New Zealand. The earthquake occurred at a complicated portion of the Australian–Pacific plate boundary, where the motion between the two plates decreases southwestward, and the azimuth changes from trench-normal to trench-parallel along the 3000 km southward-developing subduction system (Litchfield et al., 2014) (Fig. 1 inset). The epicenter of the earthquake (Fig. 1a and inset) is located at the southern end of the subducting system (Barker et al., 2009; Eberhart-Phillips and Bannister, 2010; Williams et al., 2013). The 2016 Kaikoura ¯ earthquake was not unexpected, given its plate boundary location and the historical seismicity, yet it exhibited exceptional complexity. This complexity was initially reflected by the significant non-double-couple centroid moment tensor (CMT) solutions from the USGS (USGS, 2016) and GCMT (Ekstrom et al., 2012) (Fig. 1). Subsequently, field and aerial observations and satellite radar images acquired immediately after the earthquake showed that the quake produced one of the most complex surface ruptures ever recorded (Clark et al., 2017; Litchfield et al., 2017; Stirling et al., 2017). Although the epicenter is ∼50 km inland from the coast, the accompanying tsunami caused up to 5 m of run-ups at Goose Bay, on the Bank Peninsula, to the south of the epicenter and was well recorded by  many tide gauges located along the east coast of New Zealand (Lane et al., 2017; Power et al., 2017) (Fig. S1). The seismic and tsunami hazard due to such a complex rupture cannot be faithfully characterized based on a more typical single-fault rupture scenario (Hamling et al., 2017; Shi et al., 2017). Dense geodetic measurements and strong motion seismometers onshore provided valuable near-field observations to study slip partitioning in the up-dip portion of the subduction system, as the coastline is particularly close to the trench (<50 km). Preliminary seismological analysis shows that the mechanism of the mainshock was oblique thrust (Kaiser et al., 2017). Hamling et al. (2017) derived a static slip model with more than 10 fault segments using GPS and InSAR data. The surface displacement can be fitted reasonably well from their preferred model with most of the slip occurred on crustal faults, yet they have difficulties in simulating the observed tsunami waveforms. This is partially because they did not use a fault segment for the Papatea fault as they considered the associated deformation was inelastic and they could not fit it. Hollingsworth et al. (2017) used optical satellite imagery and teleseismic data to analyze the earthquake rupture process. Their rupture model, which was derived with only seismic data assuming a two-segment fault geometry, shows a source duration of ∼100 s with unilateral rupture to the northeast and most of the slip occurring on the subduction interface. Their model is similar to the result of multiple-point source models derived from the long-period teleseismic data (Duputel and Rivera, 2017), and the result from the back-projection analysis (Zhang et al., 2017).