Mapping subduction interface coupling using magnetotellurics: Hikurangi margin, New Zealand

The observation of slow‐slip, seismic tremor, and low‐frequency earthquakes at subduction margins has provided new insight into the mechanisms by which stress accumulates between large subduction (megathrust) earthquakes. However, the relationship between the physical properties of the subduction interface and the nature of the controls on interplate seismic coupling is not fully understood. Using magnetotelluric data, we show in situ that an electrically resistive patch on the Hikurangi subduction interface corresponds with an area of increased coupling inferred from geodetic data. This resistive patch must reflect a decrease in the fluid or sediment content of the interface shear zone. Together, the magnetotelluric and geodetic data suggest that the frictional coupling of this part on the Hikurangi margin may be controlled by the interface fluid and sediment content: the resistive patch marking a fluid‐ and sediment‐starved area with an increased density of small, seismogenic‐asperities, and therefore a greater likelihood of subduction earthquake nucleation. Key Points Heterogeneous resistivity structure imaged on the plate interface on the Hikurangi subduction margin Resistivity structure correlates with plate coupling inferred by geodetic data The frictional coupling of the northern Hikurangi margin may be controlled by the interface fluid and sediment content