Effects of incoming polygonal fault systems on subduction zone and slow slip behavior（Science Advances）

Maomao Wang, Philip M. Barnes, Demian Saffer, Gregory F. Moore, Haoran Ma, Ming Wang, Jinbao Su (2025). Effects of incoming polygonal fault systems on subduction zone and slow slip behavior. Science Advances, 11(27), eadu4227. IF2025 = 12.5

Title

Effects of incoming polygonal fault systems on subduction zone and slow slip behavior

Authors

Maomao Wang^1*, Philip M. Barnes², Demian Saffer³, Gregory F. Moore⁴, Haoran Ma¹, Ming Wang¹, Jinbao Su¹

1. College of Oceanography, hohai University, nanjing, Jiangsu, china.
2. National in stitute of Water and Atmospheric Research, Wellington, new Zealand
3. University of texas institute for Geophysics, Austin, tX, USA
4. Department of earth Sciences, University of hawaii, honolulu, hi, USA

• Correspondence to: Maomao Wang(wangmm@hhu.edu.cn)

Abstract

The physical properties of subduction inputs profoundly influence megathrust slip behavior. Seismic data reveal extensive polygonal fault systems (PFSs) in the input sequences of the Hikurangi Margin and Nankai Trough. The mechanical and hydrological effects of these incoming PFSs on subduction zones are potentially substantial. Here, we investigate their effects following transport into the accretionary wedge by integrating discrete- element modeling with three- dimensional seismic interpretation. We find that the typical dips of the incoming PFSs over lap with modeled dips prone to reactivation and confirm that subducting PFSs can be reactivated and gradually evolve into major thrust faults. Comparisons with electromagnetic data indicate that PFSs may provide conduits for fluid leakage along the plate interface, coincide with disrupted strata and decreased shear stress, and enhance geometric and stress heterogeneity along the megathrust. These suggest that PFSs may play a previously unrec ognized role in contributing to shallow slow earthquake phenomena in subduction zones

Figure 2. Bathymetric map showing the location of the NZ3D seismic volume at the northern Hikurangi Margin.

(A) Regional tectonics setting. (B) Blue lines with labels are seismic slip contours (cm) for the September to October 2014 SSes (12). White transparent rectangle demarks the location of the coherent depth slice at 5140 m shown in Fig. 4c. Red star shows the location of the 1947 tsunami earthquake. Yellow circles mark the locations of iOdP expeditions 372 and 375 drilling sites. the blue and purple thick lines show the locations of the sections in (d) and Fig. 10A, respectively. (C) lithostratigraphy for iOdP site U1520 (3, 24). Bidirectional arrows indicate that PFSs develop primarily in calcareous, clay- rich sediments of Unit iv. (D) Partial section of il 135 in nZ3d showing PFSs, seamounts, décollement, proto- décollement, and slow slip. mbsf, meters below seafloor.

Figure 4. Seismic profiles and coherence depth slice from the NZ3D reflection volume showing accreted PFSs and thrust faults in the Hikurangi Margin.

(A) Perspective view of the seismic profile (il 135) and coherence depth slice (5140 m) looking northwest. (B) enlarged panel from il 135 showing PFSs, the southern part of the Pāpaku thrust, and other faults. (C) coherence depth slice at 5140 m showing the distinct expression of PFSs in the pelagic unit within the accretionary wedge. (D) crossline 2075 showing the relationship between the lateral ramp of Pāpaku thrust and PFSs through which the thrust emerges. vertical exaggeration is 1.5:1.

Figure 6. Comparison of structural deformation without and with polygonal faults in accretionary wedges based on DEM simulation.

(A) Without polygonal faults and (B to D) with polygonal faults at dip angles of θ = 35°, 45°, and 55°, respectively. The red + blue and white + blue areas represent trench fill and pelagic sediment units, respectively. T1 to T6 represent the thrust faults generated sequentially during the deformation process. The deformation strain field is superimposed on the colored layers.

Figure 7. Statistical data for modeled fault structures and maximum shear stresses field in the accretionary wedge.

(A) Probability density function of the subducting PFS fault dips calculated from seismic reflection data in hikurangi and nankai margins. the blue transparent regions of (A) to (c) represent the dip range (45° to 65°) that is most favorable for the reactivation of PFSs. (B and C) Quantity and proportion of fore- thrusts and back- thrusts faults formed in the deM Model i under various PFS fault dips. (D and E) distribution of maximum shear stresses within the wedges in the smooth reference model and the PFS- bearing model (fault dip, θ = 55°). Model shortening is 23 km.

References

Due to space limitations, please refer to the full list of references：Wang M, Barnes P M, Saffer D, et al. (2025). Effects of incoming polygonal fault systems on subduction zone and slow slip behavior. Science Advances, 11(27): eadu4227. https://www.science.org/doi/epdf/10.1126/sciadv.adu4227