A new view of interseismic coupling at the Hikurangi subduction zone, New Zealand, utilizing GNSS and InSAR data

Abstract:

We present a revised model of interseismic coupling for the Hikurangi subduction zone offshore New Zealand. Unlike our previous models, which were based only on horizontal GPS velocities, our new model includes vertical deformation rates from InSAR, and incorporates realistic elastic properties into our inversions, rather than assuming a uniform, elastic half space. The latter is particularly important to consider at subduction zones, where there are strong contrasts in the elastic properties of the slab and forearc, which influence the resulting deformation field. Our new model reveals a more heterogeneous distribution of coupling than previously published models. Similar to previous studies, we observe deep locking of the southern Hikurangi subduction interface, and a largely creeping interface in the northern and central portion of the subduction zone. However, the new model highlights additional, discrete patches of locking embedded within the mostly creeping interface at the central and northern Hikurangi margin. These patches of coupling are also resolved as regions of elevated contractional strain along the North Island’s east coast, in newly developed strain rate maps based on GNSS horizontal velocities. We will compare our coupling model with distributions of slow slip events, and past earthquakes from paleoseismic studies, and the implications of this for spatio-temporal variations in slip behaviour. We will also discuss the relationship of our new estimates of interseismic coupling to geophysical inferences of the presence of fluids in the region of the plate interface and the upper plate, and the potential role of fluids and structural changes in controlling slip behaviour at the Hikurangi subduction zone.