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Stress transition from horizontal to vertical forces during subduction initiation


Subduction zones are fundamental to plate tectonics, yet how they initiate remains enigmatic. Geodynamic models suggest that if horizontal forces dominate, the upper plate experiences compression and uplift followed by extension and subsidence, whereas vertically forced subduction involves only extension. Geologic evidence of past subduction initiation events has been interpreted in terms of these alternatives; however, it is unclear whether they are mutually exclusive or represent different stages of early subduction. Here, we present seismic images of the Puysegur plate boundary south of New Zealand that reveal space–time relations of stress during subduction initiation. Our data show evidence for a stress transition (compression followed by extension) that spread from north to south as the trench nucleated and propagated along the plate boundary. Both the magnitude and duration of compression diminish from north (8 Myr) to south (5 Myr). This indicates that transition to self-sustaining subduction accelerates after nucleation of a downgoing slab increases driving forces and decreases fault strength near the propagating tipline of the nascent trench. Instead of horizontally forced versus vertically forced initiation, we propose a four-dimensional evolution, where horizontal forces initially dominate at the site of nucleation, but with time, vertical forces accelerate, propagate along strike and facilitate the development of self-sustaining subduction.

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Fig. 1: Tectonic setting of the Puysegur margin.
Fig. 2: Seismicity and seismic reflection images.
Fig. 3: Stress evolution along the margin.
Fig. 4: Interpretation of Puysegur margin crossing seismic profiles.
Fig. 5: Cartoon summary of subduction initiation.

Data availability

Uninterpreted and interpreted seismic images shown in this study can be found in the Extended Data (Extended Data Figs. 37). Seismic data from the SISIE expedition are available through the Marine Geoscience Data System ( Underway geophysical data from MGL1803 are available from the Rolling Deck Repository ( Earthquake moment tensors can be accessed online from the gCMT ( and GeoNet ( catalogues. Regional bathymetry data are available through NIWA ( and gravity grids from GNS Science (

Code availability

Maps were generated using the Generic Mapping Tools (GMT) software (


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We thank the captain, crew and science party of the RV Marcus Langseth for their efforts during the South Island Subduction Initiation Experiment. Thank you to the University of Texas Institute for Geophysics (UTIG) Marine Geology and Geophysics group for fruitful discussion and feedback, which enhanced this work. Research in this manuscript was supported by the National Science Foundation through awards OCE-1654689 (UT Austin), OCE-1654766 and OCE-2049086 (Caltech). B.S. is grateful for support from a UTIG Ewing and Worzel Graduate Fellowship. This is UTIG contribution no. 3864.

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Authors and Affiliations



H.J.A.V.A., S.P.S.G., M.G., J.S. and R.S. led acquisition of the SISIE seismic dataset. B.S. conceived the study, reprocessed the EW9601-P1 seismic data and wrote the bulk of the manuscript. B.S. and S.P.S.G. conducted the detailed interpretation of seismic reflection data. S.P.S.G. and H.J.A.V.A. oversaw the project and the analyses. M.G. and R.S. were instrumental in developing the conceptual model of subduction initiation. All authors contributed to writing the manuscript through edits and the concepts outlined in this paper through feedback and discussions.

Corresponding author

Correspondence to Brandon Shuck.

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The authors declare no competing interests.

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Peer review information

Nature Geoscience thanks Fabio Crameri, Susan Ellis and Marc-Andre Gutscher for their contribution to the peer review of this work. Primary Handling Editor: Rebecca Neely, in collaboration with the Nature Geoscience team.

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Extended data

Extended Data Fig. 1 Seismicity and location of the subducting slab at the Puysegur plate boundary.

Seismicity outlines a clear Benioff zone along the Puysegur margin. Earthquakes from the global Centroid Moment Tensor and GeoNET catalogs. Depth of seismic events are not well resolved offshore. The basal leading edge of the subducting slab is shown as cyan lines. Beneath Fiordland, the present day slab edge is well defined from the Benioff zone and inferred in the offshore domain. The ancient leading edge of the slab is updated after Sutherland et al. 37 and inferred from surface effects in Fiordland, as evidenced by thermochronology data. For a reconstruction of the unfolded slab position see Sutherland et al. 24.

Extended Data Fig. 2 Gravity map of the Puysegur margin.

Regional Free-Air gravity anomaly map (grid from GNS,; McCubbine et al., 2017). Dashed green line shows the gravity trace that was extracted for the residual calculation and plotted on Fig. 3. Elevation grid plotted in semi-transparent grayscale is draped on the gravity grid to guide visualization of the Free-Air anomaly relative to prominent features along the Puysegur margin.

Extended Data Fig. 3 Seismic reflection image of the Tauru Fault Zone.

Uninterpreted (top) and interpreted (bottom) pre-stack depth migrated seismic reflection image of the Tauru Fault Zone.

Extended Data Fig. 4 Seismic reflection image of the S3N structure.

Uninterpreted (top) and interpreted (bottom) pre-stack depth migrated seismic reflection image of S3N.

Extended Data Fig. 5 Seismic reflection image of the S3S structure.

Uninterpreted (top) and interpreted (bottom) pre-stack depth migrated seismic reflection image of S3S.

Extended Data Fig. 6 Seismic reflection image of the S1 structure.

(Top) Backscatter mosaic showing higher amplitude returns corresponding to the breach of S1 fold crests at the seafloor. Uninterpreted (middle) and interpreted (bottom) pre-stack depth migrated seismic reflection image of S1.

Extended Data Fig. 7 Seismic reflection image of the EW9601-P1 profile.

Uninterpreted (top) and interpreted (bottom) pre-stack depth migrated seismic reflection image of the EW9601-P1 profile.

Extended Data Fig. 8 Global compilation of subduction initiation events in the last ~110 Ma from the SZI Database 1.0 (Crameri et al., 6).

Circles indicate locations of recent SZI in the Miocene, whereas squares represent older SZI events. All SZI events shown formed nearby existing subduction zones. Left-hand side color of symbols reflects whether or not subduction formed on a pre-existing plate boundary, while the right-hand side color of symbols depicts the affinity of the overriding plate.

Extended Data Fig. 9 Schematic of 4D force evolution during subduction initiation (modified after Gurnis et al., 2004).

a. Curves represent whether forces are resisting or driving subduction locally at their corresponding locations in b. The time to self-sustaining subduction and overall resistance decreases for locations where subduction is propagating through. b. Initial block diagram of a future subduction zone at a continent-ocean transition.

Extended Data Table 1 Measured throw (m) across fault planes for each unit horizon top

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Shuck, B., Gulick, S.P.S., Van Avendonk, H.J.A. et al. Stress transition from horizontal to vertical forces during subduction initiation. Nat. Geosci. 15, 149–155 (2022).

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