14 Years of Slip on the Hikurangi Subduction Zone

Abstract

Slow slip events (SSEs) on the Hikurangi subduction megathrust in New Zealand have been studied extensively. However, we lack a comprehensive and consistent catalog over a long time period since 2010. Recent studies have focused on short time periods and rarely provide a time dependent image of slip during SSEs, let alone between SSEs. In addition, the use of different methods, parametrizations and data sets does not allow to compare SSEs at different periods of time. Our study aims to model the spatio-temporal history of slip of the subduction, devoid of temporal smoothing, over the entire 2009–2023 time period based on GNSS time series. We combine an Independent Component Analysis decomposition with an inversion scheme to derive a history of accelerations and slowdowns of aseismic fault slip on the megathrust. We then combine a SSE detection procedure with an inter-SSE linear trend correction to reference this slip time series to the inter-SSE loading rate and build a catalog of 27 SSEs. We observe a change in the behavior of SSEs after the 2016 Kaikoura earthquake with respect to the pre-Kaikoura period, highlighted by changes in the slip frequency content. We finally evaluate using a Bayesian approach the subduction inter-SSE coupling map, the SSEs cumulative slip between 2009 and 2023, to constrain the distribution of locked regions over 14 years and conclude that moment deficit accumulates mostly under Wellington peninsula at a rate of 4.9 ± 0.5 10¹⁸ N.m/yr.