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Fracture damage patterns around faults induced by dynamic earthquake rupture are an invaluable record to clarify the rupture process on complex fault networks. The 2016 M-w 7.8 Kaikoura earthquake in New Zealand has been reported as one of the most complex earthquakes ever documented that ruptured at least 15 crustal faults. High-resolution optical satellite image displacement maps provide distinctive profiles of displacement across the faults and help visualize the off-fault damage pattern. They are combined with field observation and coupled with a numerical tool that captures the dynamics of the rupture and simultaneous activation of off-fault damage to allow the determination of the most likely rupture scenario. This study demonstrates that complex rupture processes can be explained in a rather simple way via a synergetic combination of state-of-the-art observation and first principle physics-based numerical modeling of off-fault damage.

Plain Language Summary In a first-of-its-kind work, we combine optical image correlation at a resolution never achieved before (1.8-m ground resolution), field observations, and a unique dynamic rupture simulation tool, including off-fault deformation, to unravel, beyond doubt, part of the Kaikoura rupture process. We show that matching observed off-fault deformation pattern with rupture simulation helps easily identify the earthquake rupture path to propose a kinematically simple earthquake scenario. Thus, this work shows that when building models of seismic hazard, like in Southern California, systematic consideration of off-fault damage patterns for past events would help understand earthquake scenario and to model future events. Hence, this presents a great potential to narrow down the multitude of rupture scenarios along complex fault networks that need to be considered in seismic hazard model assessment.