Geodetic resolution of the interplay between earthquakes and slow slip in the Hikurangi margin

Slow‑slip events and their interactions with earthquakes remain poorly understood. To investigate such interactions, we examine a deep, two-year M7 slow slip event which started in 2021 in the central Hikurangi subduction zone, which also coincided with a period of several moderate (Mw 4-5+) earthquakes in the region. We analyze six years (2018–2024) of continuous GNSS data from 97 stations across New Zealand's North Island. Three different methods are assessed to retrieve time-dependent slip at depth: (1) fixed‑window static offsets (1, 3, 6 months); (2) Independent Component Analysis-based inversion Method (ICAIM); and (3)~a simplex minimization approach utilizing TDefnode. All three methods yield a consistent, high‑resolution slip history in time and space. The 2021-2024 long-term, deep slow slip event (equivalent Mw 7.1-7.2) evolves with five to six distinct sub-events, three of which represent an increase in slow-slip event moment release within weeks after Mw4+ intraslab earthquakes. In contrast, plate interface events (M_w>5) during this period do not seem to impact the slow slip event evolution. Static Coulomb modeling of stress changes due to long-term slow slip events prior to two interface earthquakes show positive stress changes of 20–60kPa at the earthquake hypocenters, suggesting that slow slip events may have played a role in triggering these interface events. Our results highlight that Hikurangi slow slip events and moderate earthquakes engage in two‑way communication at considerably lower magnitudes than documented elsewhere, underscoring the value of real‑time geodetic monitoring for seismic hazard assessment.