ALBERT

Description: The coupling at the interface between tectonic plates is a key geophysical parameter to capture the frictional locking across plate boundaries and provides a means to estimate where tectonic strain is accumulating through time. Here, we use both interferometric radar (InSAR) and Global Navigation Satellite System (GNSS) data to investigate the plate coupling of the Hikurangi subduction zone beneath the North Island of New Zealand, where multiple slow slip cycles are superimposed on the long‐term loading. We estimate the plate coupling across the subduction zone over three multi‐year observational periods targeting different stages of the slow slip cycle. Our results highlight the importance of the observational time period when interpreting coupling maps, emphasizing the temporal variability of plate coupling. Leveraging multiple geodetic data sets, we demonstrate how InSAR provides powerful constraints on the spatial resolution of both plate coupling and slow fault slip, even in a region where a dense GNSS network exists. Plain Language Summary Plate coupling as a concept describes to what degree the boundaries between tectonic plates are locked and building up stress. Such accumulated stress (over hundreds to thousands of years) will eventually be released in earthquakes, and therefore provides important information about the potential for future earthquakes. Our study uses satellite data to investigate how coupling between tectonic plates along the Hikurangi subduction zone (New Zealand's largest and most dangerous plate boundary fault) changes with time. We analyzed Interferometric Synthetic Aperture Radar and Global Navigation Satellite System data to map the areas where the plates are stuck together (coupled) and where they move past each other (uncoupled). We show that plate coupling varies significantly in space over 2, 4, and 10‐year time scales, highlighting the importance of carefully considering the observational time period when interpreting coupling maps. Key Points Integration of high‐resolution displacement maps from radar imagery captures plate coupling at fine scales Estimates of plate coupling depend strongly on the time period over which surface velocities are measured Temporal variations in plate coupling highlight when and where slow slip dominates the slip budget