# Structural barriers control the spatial extent of slow earthquake slip

## TL;DR

This study identifies structural barriers that control the spatial extent of slow earthquake slip in the Nankai Trough, helping predict future megathrust rupture limits.

## Contribution

The study integrates multiple datasets to show how structural boundaries limit slow earthquake slip in subduction zones.

## Key findings

- Tremor activity limits align with structural boundaries like décollement kinks and fault zones.
- Megathrust geometry, material properties, and fluid distribution jointly control slow earthquake extent.
- Subducted ridges influence the spatial limits of slow slip events.

## Abstract

Recent seismological and geodetic observations have revealed shallow slow earthquakes on subduction megathrusts, offering an opportunity to explore the factors controlling megathrust slip. Identifying these controlling factors helps constrain the potential updip extent of future megathrust ruptures. Here, we investigate the factors controlling the spatial extent of shallow slow earthquakes by integrating tremor locations with uncertainty estimates, detailed bathymetry data, and multichannel seismic data for the 2020–2021 slow earthquake sequence in the Kumano-nada region of the Nankai Trough. Tremor probability maps reveal that the updip, downdip, and lateral limits of tremor activity coincide with distinct structural boundaries. These include the kink or branching of the décollement, a deep-seated strike-slip fault, and the inner–outer wedge boundary. These structures likely act as geometrical or mechanical barriers, further influenced by variations in pore-fluid pressure and by the subducted Paleo–Zenisu ridge. The results indicate that megathrust geometry, material properties of the overriding prism, fluid distribution, and ridge subduction jointly govern the spatial extent of slow earthquakes, emphasizing the need to account for these factors in assessing the potential extent of future megathrust ruptures.

This study shows that slow earthquake slip in the Nankai Trough is confined by structural barriers, including fault geometry, material contrasts, and subducted ridges, revealing key controls on the potential extent of future megathrust ruptures.