The role of subducting topography on the mode of fault slip—particularly whether it hinders or facilitates large megathrust earthquakes—remains a controversial topic in subduction dynamics^1,2,3,4,5. Models have illustrated the potential for subducting topography to severely alter the structure, stress state and mechanics of subduction zones^4,6; however, direct geophysical imaging of the complex fracture networks proposed and the hydrology of both the subducting topography and the associated upper plate damage zones remains elusive. Here we use passive and controlled-source seafloor electromagnetic data collected at the northern Hikurangi Margin, New Zealand, to constrain electrical resistivity in a region of active seamount subduction. We show that a seamount on the incoming plate contains a thin, low-porosity basaltic cap that traps a conductive matrix of porous volcaniclastics and altered material over a resistive core, which allows 3.2 to 4.7 times more water to subduct, compared with normal, unfaulted oceanic lithosphere. In the forearc, we image a sediment-starved plate interface above a subducting seamount with similar electrical structure to the incoming plate seamount. A sharp resistive peak within the subducting seamount lies directly beneath a prominent upper plate conductive anomaly. The coincidence of this upper plate anomaly with the location of burst-type repeating earthquakes and seismicity associated with a recent slow slip event⁷ directly links subducting topography to the creation of fluid-rich damage zones in the forearc that alter the effective normal stress at the plate interface by modulating the fluid overpressure. In addition to severely modifying the structure and physical conditions of the upper plate, subducting seamounts represent an underappreciated mechanism for transporting a considerable flux of water to the forearc and deeper mantle.

俯冲地形对断层滑动模式的作用——特别是它是否阻碍或促进大型逆冲地震——仍然是俯冲动力学中一个有争议的话题^1,2,3,4,5。模型已经说明俯冲地形有可能严重改变俯冲带的结构、应力状态和力学^4,6; 然而，所提出的复杂裂缝网络的直接地球物理成像以及俯冲地形和相关的上板块损伤带的水文学仍然难以捉摸。在这里，我们使用在新西兰希库兰吉边缘北部收集的被动和受控源海底电磁数据来限制主动海山俯冲区域的电阻率。我们表明，进入板块上的海山包含一个薄的、低孔隙率的玄武岩盖，该盖将多孔火山碎屑和蚀变材料的导电基质困在电阻核上，与正常的、无断层的相比，这允许多 3.2 到 4.7 倍的水俯冲大洋岩石圈。在前弧中，我们对俯冲海山上方沉积物匮乏的板块界面进行了成像，该海山具有与进入的板块海山相似的电气结构。俯冲海山内的尖电阻峰直接位于突出的上板块导电异常下方。该上板块异常与爆发型重复地震的位置以及与最近的慢滑动事件相关的地震活动的巧合^图7直接将俯冲地形与弧前富含流体的损伤区的形成联系起来，这些损伤区通过调节流体超压来改变板块界面处的有效法向应力。除了严重改变上板块的结构和物理条件外，俯冲海山代表了一种将大量水输送到弧前和更深的地幔的机制，这一机制未被充分认识。