DataSheet1_Trench topography in subduction zones: A reflection of the plate decoupling depth.PDF

Subduction of lithospheric plates produces narrow, linear troughs (trench) in front of the overriding plates at the convergent boundaries. The trenches show a wide variation in their topographic characteristics, such as width, vertical depth, and bounding surface slopes. Benchmarking their controlling factors is thus a crucial step in the analysis of trench morphology. This article identifies the mechanical coupling between the subducting and overriding plates as a leading factor in modulating the topographic evolution of a trench. The maximum depth of decoupling (MDD) is used to express the degree of decoupling at the plate interface. We simulate subduction zones in computational fluid dynamic (CFD) models to show the topographic elements (maximum negative relative relief: D; fore- and hinter-wall slopes: θF and θH; opening width: W) of trenches as a function of the MDD within a range of 30–120 km. Both D and θ strongly depend on the MDD, whereas W is found to be relatively less sensitive to the MDD, implying that the narrow/broad width of a trench can change little with the plate decoupling factor. We also show that the MDD critically controls the fore-arc stress fields of a trench, switching a compressive to tensile stress transition with increasing MDD. This study finally validates the model findings with well-constrained natural trench topography.

岩石圈板块俯冲作用在汇聚边界处的上覆板块前方形成狭窄的线性洼地——海沟（trench）。海沟的地形特征差异显著，涵盖宽度、垂直深度及边界坡面等要素。明确其控制因素并开展基准性分析，是海沟形态研究的关键环节。本文明确俯冲板块与上覆板块间的机械耦合作用，是调控海沟地形演化的主导因素。我们采用板块界面解耦最大深度（MDD）表征板块界面的解耦程度。通过计算流体动力学（CFD）模型对俯冲带开展数值模拟，结果表明海沟的各类地形要素：最大负相对起伏D、前壁与后壁坡度θ_F和θ_H、张开宽度W，均随30~120 km范围内的MDD发生变化。其中D与坡度θ均显著依赖于MDD，而W对MDD的敏感性相对较弱，这意味着海沟的宽窄程度随板块解耦因子的变化幅度极小。此外，研究还发现MDD对海沟的弧前应力场具有关键调控作用：随着MDD增大，应力场会从压应力状态向张应力状态转变。本研究最终通过约束条件完善的天然海沟地形数据，验证了模型模拟结果的合理性。