New Zealand represents the subaerial portion of the mostly submerged microcontinent Zealandia, which straddles the Pacific and Australian plate boundary. Subduction occurs on either side of the transform Alpine Fault, which spans most of New Zealand's South Island. The polarity of subduction reverses: the Australian Plate subducts at the incipient Fiordland Subduction Zone south of the Alpine Fault and the Pacific Plate subducts at the Hikurangi Subduction Zone in the north. The subaqueous nature of the continental crust, subduction polarity reversal across a transform fault, and the young age of the Fiordland subduction zone are all features that make Zealandia an interesting area of study. Here, we use teleseismic Rayleigh wave data in a two-station interferometric method to create a new 3D Vs model of Zealandia's upper mantle focused around New Zealand. Our dataset combines both onshore and offshore seismometer readings covering an area ~1.4 million km^2 to a depth of 200 km. Our results corroborate the presence of the Hikurangi Plateau beneath South Island and reveal how it connects to the Hikurangi Subduction Zone beneath the Marlborough Fault System. A mostly offshore large subcrustal low-velocity structure northwest of North Island that connects both to Mount Taranaki and the Auckland Volcanic Field is present. Other resolved structures include the Australian Plate beneath the Alpine Fault and offshore remnant structures related to the East Gondwana Subduction Zone. These improved constraints on mantle structure beneath New Zealand provide critical geodynamic context for understanding plate-boundary processes that control seismic and volcanic hazards.