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Abstract Fluid generation and migration regulate the development of pore fluid pressure, which is hypothesized to influence the occurrence of slow slip events at subduction zones. Seafloor seep sites present the opportunity to directly sample fluids flowing through the accretionary wedge and assess the hydrogeologic conditions of the outer forearc. We present heat flow measurements and pore water geochemistry from sediment cores collected at fault‐hosted seep sites on the southern and northern Hikurangi margin, offshore the North Island of New Zealand. These measurements span the deformation front to the shelf break. Along the northern margin, heat flow data do not show anomalies that can be obviously attributed to the discharge of warm fluids. Pore fluid compositions indicate that seep fluids originate from compaction within the uppermost wedge. Reactive‐transport modeling of pore water solute profiles produces fluid flow rate estimates ≤2 cm/yr. Shallow fluid sources and low discharge rates at offshore fault‐hosted seeps suggest that the sampled fault zones are characterized by low permeability at depth, preventing efficient drainage of the megathrust and underthrust sediments to the seafloor. These results provide additional evidence that the northern Hikurangi margin plate boundary is associated with high pore fluid pressures that likely act as a control on slow slip activity.
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This content will become publicly available on February 27, 2027
Active protothrusts and fluid highways: Seismic noise reveals hidden subduction dynamics in Cascadia
Complex interactions between strain accumulation, fault slip, and fluid migration influence shallow subduction zone dynamics. Using a decade of continuous ambient seismic data from Cascadia’s seafloor observatories, we identified distinct regional variations in subduction dynamics. Northern Cascadia exhibits a fully locked megathrust with persistent strain accumulation, while central Cascadia displays a slow slip event on protothrusts and rapid fluid migration along fault systems in the overriding plate. Effective fluid transport through the décollement and the Alvin Canyon Fault likely modulates the earthquake behavior but does not cause slow slip events on the megathrust and likely stabilizes large earthquakes, promoting rupture arrest.
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- Award ID(s):
- 2103701
- PAR ID:
- 10712434
- Publisher / Repository:
- American Association for the Advancement of Science (AAAS)
- Date Published:
- Journal Name:
- Science Advances
- Volume:
- 12
- Issue:
- 9
- ISSN:
- 2375-2548
- Page Range / eLocation ID:
- eaea3684
- Subject(s) / Keyword(s):
- Cascadia subduction zone ambient seismic noise slow slip protothrusts fluid migration
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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