Effect of Buoyant Sediment Overlying Subducting Plates on Trench Geometry: 3D Viscoelastic Free Subduction Modeling

Abstract

Buoyant trench sediment generates an isostatic restoring force that opposes the slab pull of subducting plates; however, the influence of this force on subduction dynamics is poorly understood. Here, we performed three-dimensional free subduction simulations adopting a variety of sediment distributions along a trench to investigate the correlation between trench motions and heterogeneous buoyant forces. Two endmembers, sediment-rich and sediment-starved centers, induced convex and concave trenches, respectively. The trench curvatures obtained from the natural subduction zones are well constrained by our models over wide magnitudes (1–9 km) and wavelengths (100–400 km) of deficient and excess sediments. Conversely, a uniform sediment distribution leads to an extremely narrow range of trench curvatures. These results imply that trench sediment contributes significantly to deviated curvatures along trench strikes. Finally, we observed stress localization at shallow slab hinges that lie beneath abundant sediments, clarifying the relationship between sediment thickness and subduction earthquakes.