Nitheshnirmal Sadhasivam, Ling Chang, Hakan Tanyas 

Strong earthquakes are not only able to change the earth's surface processes by triggering a large population of coseismic landslides but also by influencing hillslope deformation rates in post-seismic periods. An increase in post-seismic hillslope deformation rates could also be linked to a change in post-seismic landslide hazard level and, thus, could be exploited to better assess post-seismic landslide risk in a given area. However, variations in hillslope deformations from pre- to post-seismic phases have rarely been examined for strong earthquakes. This paper examines pre- and post-seismic hillslope deformations, from 2014 to 2018, for a large area (~2,300 km2) affected by the 2016 Mw7.8 Kaikōura earthquake using time series Interferometric Synthetic Aperture Radar (InSAR) techniques. To consistently analyze the entirety of the area from pre- to post-seismic phases, we aggregate InSAR-derived deformations for geomorphologically meaningful landscape partitions called Slope Units. We further examine the aggregated data through the hillslope deformation scheme, which we propose as a method to systematically identify the variations in post-seismic hillslope deformation trends. In this context, we label newly activated, uninterruptedly deforming, and stabilized hillslopes in the post-seismic phase. Our results show an ~130% increase in mean annual line-of-sight velocity after the earthquake. Overall, the areas affected by larger ground shaking show higher post-seismic deformations, which highlights the importance of the earthquake legacy effect as a factor controlling post-seismic hillslope deformations.