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

## TL;DR

This study explores how polygonal fault systems in subduction zones affect megathrust slip behavior and contribute to slow earthquakes.

## Contribution

The study reveals that polygonal fault systems can evolve into major thrust faults and influence slow slip events through stress and geometric heterogeneity.

## Key findings

- Incoming polygonal fault systems can reactivate and evolve into major thrust faults.
- PFSs may act as fluid conduits, reducing shear stress and increasing heterogeneity along the megathrust.
- These fault systems may contribute to shallow slow earthquake phenomena in subduction zones.

## 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 overlap 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 unrecognized role in contributing to shallow slow earthquake phenomena in subduction zones.

Subduction of polygonal fault systems enhance geometric and stress heterogeneity along the megathrust, promoting slow slip events.