Detection of landslide timing, reactivation and precursory motion during the 2018, Lombok, Indonesia earthquake sequence with Sentinel-1

Abstract. Earthquake-triggered landslides can be mapped using optical satellite images, but assessing how they evolve through time during sequences of earthquakes is difficult with such data due to cloud cover. Here we use Sentinel-1 techniques to characterise the evolution of rapid landslides during the 2018 Lombok, Indonesia earthquake sequence. While the majority of new landslides were triggered during the largest earthquake in the sequence on 05/08, we are also able to identify landslide activity associated with other, lower magnitude earthquakes on 28/07, 09/08 and 19/08, with many landslides active in more than one earthquake. In particular, many landslides triggered by the 05/08 earthquake were then reactivated later in the sequence. These reactivations were triggered by accelerations as weak as 0.1 g, while new failures generally did not occur below 0.15 g, suggesting a post-seismic weakening effect driven by the landslides themselves rather than general landscape weakening. We also identified at least one example where precursory motion during the first earthquake in the sequence was later followed by larger scale failure. Overall, we demonstrate that Sentinel-1 amplitude and coherence are valuable tools to study how landslide hazard and mass wasting evolve during sequences of triggers.