Subduction zone coupling and tectonic block rotations in the North Island, New Zealand

TLDR

The GPS velocity field in New Zealand’s North Island is dominated by long‑term tectonic rotation of the eastern island and elastic strain from stress buildup on the subduction‑zone thrust fault. The study aims to map interseismic coupling along the subduction‑zone interface and quantify the kinematics of tectonic block rotations. This was achieved by jointly inverting GPS velocities, earthquake slip vectors, and geological fault slip rates to determine block angular velocities and spatially variable fault coupling. The results show a high slip‑rate deficit at the southern interface that decreases northward, multiple clockwise‑rotating blocks (0.5–3.8 deg Myr⁻¹) that accommodate margin‑parallel motion, a link between eastern rotation and the thickening Hikurangi Plateau, and broader implications for rapid block rotations and slip partitioning at convergent margins.

Abstract

The GPS velocity field in the North Island of New Zealand is dominated by the long‐term tectonic rotation of the eastern North Island and elastic strain from stress buildup on the subduction zone thrust fault. We simultaneously invert GPS velocities, earthquake slip vectors, and geological fault slip rates in the North Island for the angular velocities of elastic crustal blocks and the spatially variable degree of coupling on faults separating the blocks. This approach allows us to estimate the distribution of interseismic coupling on the subduction zone interface beneath the North Island and the kinematics of the tectonic block rotations. In agreement with previous studies we find that the subduction zone interface beneath the southern North Island has a high slip rate deficit during the interseismic period, and the slip rate deficit decreases northward along the margin. Much of the North Island is rotating as several, distinct tectonic blocks (clockwise at 0.5–3.8 deg Myr −1 ) about nearby axes relative to the Australian Plate. This rotation accommodates much of the margin‐parallel component of motion between the Pacific and Australian plates. On the basis of our estimation of the block kinematics we suggest that rotation of the eastern North Island occurs because of the southward increasing thickness of the subducting Hikurangi Plateau. These results have implications for our understanding of convergent margin plate boundary zones around the world, particularly with regard to our knowledge of mechanisms for rapid tectonic block rotations at convergent margins and the role of block rotations in the slip partitioning process.