Slow-Moving Landslides Triggered by the 2016 Mw 7.8 Kaikoura Earthquake, New Zealand: A New InSAR Phase-Gradient Based Time-Series Approach

Earthquake-triggered slow-moving landslides are not well studied mainly due to a lack of high-resolution in-situ geodetic observations both in time and space. Satellite-based interferometric synthetic aperture radar (InSAR) has shown potential in landslides applications, however, it is challenging to detect earthquake-triggered slow-moving landslides over large areas due to the effects of post-seismic tectonic deformations, atmospheric delays, and other spatially propagated errors (e.g., unwrapped errors caused by decorrelation noises). Here, we present a novel InSAR phase-gradient-based time-series approach to detect slow-moving landslides that triggered by the 2016 Mw 7.8 Kaikoura earthquake. Twenty-one earthquake-triggered large (>0.1 km(2)) slow-moving landslides are detected and studied. Our results reveal decaying characteristics of the temporal evolutions of these landslides, that averagely 3.9 years after the earthquake, their post-seismic velocity will decay by 90% to reach approximately the pre-seismic level. Our study opens new perspectives for understanding mass balance of earthquakes and helps reduce associated hazards.