Changes in electrical resistivity track changes in tectonic plate coupling

Interplate coupling on the Hikurangi subduction margin along the east coast of New Zealand's North Island changes north to south from almost uncoupled to locked. Clay‐rich sediments and aqueous fluids at the subduction interface have been invoked as key factors in the frictional processes that control interplate coupling. Here we use magnetotelluric data to show that the subduction interface in the weakly coupled region is electrically conductive but is resistive in the locked region. These results indicate the presence of a layer of fluid‐ and clay‐rich sediments in the weakly coupled region and support the idea that the presence of fluid and hydrated clays at the interface is a major factor controlling plate coupling. Key Points Electrical resistivity images of the Hikurangi subduction margin The subduction interface is conductive in the weakly coupled part of the margin The subduction interface is resistive in the locked part of the margin