The pre-2004 9.0 Aceh earthquake Global Positioning System (GPS) velocity field along the western margin of the Sunda plate was dominated by the long-term secular velocity and elastic strain. Since then a sequence of the great earthquakes includes the 2005 8.6 Nias, 2007 8.5 Bengkulu, and 2012 8.6 and 8.2 Wharton Basin earthquakes, have occurred in different segments of the subduction zone and its vicinity, which resulted in significant coseismic and postseismic deformation on the Sunda plate. This study combined the published and the estimated GPS velocity fields between 1991–2016 from more than 150 GPS sites. These velocity fields are inverted to examine the angular velocities of the elastic crustal blocks and the variability of the coupling on the subduction trench. This analysis reveals the characteristic of the Sunda subduction interface over multiple earthquake cycles along different segments of the trench, whereby the subduction interface coupling coefficient changed both spatially and temporally after each rupture. The strongly coupled subduction interface along the plate convergence before 2004 earthquake is now partially coupled to freely slipping in the segments that ruptured during the 2005 and 2007 earthquakes, according to the present-day GPS velocity field (2012.2–2016.0). Interestingly, the best fitting model shows that the Siberut segment (0.5–2.0°S) remained fully coupled throughout the years. The result implies that the level of coupling along the highly segmented Sunda subduction interface varies over time, and that the great earthquake rupture was likely to be a result of the variation in the coupling.

Anticipating and managing the impacts of sea-level rise for nations astride active tectonic margins requires rates of sea surface elevation change in relation to coastal land elevation to be understood. Vertical land motion (VLM) can either exacerbate or reduce sea-level changes with impacts varying significantly along a coastline. Determining rate, pattern, and variability of VLM near coasts leads to a direct improvement of location-specific relative sea level (RSL) estimates. Here, we utilise vertical velocity field from interferometric synthetic aperture radar (InSAR) data, calibrated with campaign and continuous Global Navigation Satellite System (GNSS), to determine the VLM for the entire coastline of New Zealand. Guided by existing knowledge of the seismic cycle, the VLM data infer long-term, interseismic rates of land surface deformation. We build probabilistic RSL projections using the Framework for Assessing Changes to Sea-level (FACTS) from IPCC Assessment Report 6 and ingest local VLM data to produce RSL projections at 7435 sites, thereby enhancing spatial coverage that was previously limited to tide gauges. We present ensembles of probability distributions of RSL for medium confidence climatic processes for each scenario to 2150 and low confidence processes to 2300. For regions where land subsidence is occurring at rates >2mm yr-1 VLM makes a significant contribution to RSL projections for all scenarios out 2150. Beyond 2150, for higher emissions scenarios, the land ice contribution to global sea level dominates. We discuss the planning implications of RSL projections, where timing of threshold exceedance for coastal inundation can be brought forward by decades.