Seismological characterization of northern Hikurangi margin slow slip regions associated with normal faults, seamounts and seeps
Author(s)
Type
Journal Article
Abstract
At the northern Hikurangi margin, Aotearoa New Zealand, slow slip events (SSEs) recur every 6–24 months to ∼30 km depth. Although shallow SSEs (0–10 km) are well-studied offshore, the deeper portion (10–30 km) remains poorly understood, limiting insight into SSE initiation. Here we investigate this deeper region and examine relationships between newly resolved SSEs and seismicity. Using time-dependent inversions, we resolve two small SSEs (MW 6.2 and 6.4), including one that extends from 15 to 30 km depth. Using data from a dense onshore seismograph network deployed directly above this deeper portion from December 2017 to October 2018, we construct a catalog of 3,071 high-quality earthquakes with hypocentral uncertainties ≤5 km, located with a 3-D velocity model and a new 1-D model.
Earthquake magnitudes range from -0.84 to 4.40, with a completeness magnitude of 1.7 and a b-value of 1.06. Focal mechanisms reveal numerous normal-faulting earthquakes, including some within the slab mantle. Vertically-aligned seismicity and normal-faulting earthquakes outline pathways linking the slab mantle to surface seeps of mantle-derived fluids. We infer that normal faults form due to slab bending and localized uplift of subducting seamounts, which roughen the plate interface, damage the upper plate, and promote fluid migration. Land-ward of ∼100 km from the trench, both surface seeps and normal-faulting mechanisms ceasecoinciding with the downdip limit of shallow SSEs. Together, these results suggest that the Hikurangi margin’s rough subducting plate interface exerts strong control on forearc dewatering and SSE genesis.
Earthquake magnitudes range from -0.84 to 4.40, with a completeness magnitude of 1.7 and a b-value of 1.06. Focal mechanisms reveal numerous normal-faulting earthquakes, including some within the slab mantle. Vertically-aligned seismicity and normal-faulting earthquakes outline pathways linking the slab mantle to surface seeps of mantle-derived fluids. We infer that normal faults form due to slab bending and localized uplift of subducting seamounts, which roughen the plate interface, damage the upper plate, and promote fluid migration. Land-ward of ∼100 km from the trench, both surface seeps and normal-faulting mechanisms ceasecoinciding with the downdip limit of shallow SSEs. Together, these results suggest that the Hikurangi margin’s rough subducting plate interface exerts strong control on forearc dewatering and SSE genesis.
Date Issued
2026-01-01
Date Acceptance
2026-01-05
Citation
Journal of Geophysical Research (JGR): Solid Earth, 2026, 131 (1)
ISSN
2169-9313
Publisher
American Geophysical Union
Journal / Book Title
Journal of Geophysical Research (JGR): Solid Earth
Volume
131
Issue
1
Copyright Statement
© 2026. The Author(s).This is an open access article under theterms of the Creative Commons Attribution License, which permits use,distribution and reproduction in anymedium, provided the original work isproperly cited.
License URL
Identifier
10.1029/2025JB032916
Publication Status
Published
Article Number
2025JB032916
Date Publish Online
2026-01-17