Recent geodetic studies have shown that slow-slip events can occur on subduction faults, including their shallow (<15 km depth) parts where tsunamis are also generated. Although observations of such events are now widespread, the physical conditions promoting shallow slow-slip events remain poorly understood. Here we use full waveform inversion of controlled-source seismic data from the central Hikurangi (New Zealand) subduction margin to constrain the physical conditions in a region hosting slow slip. We find that the subduction fault is characterized by compliant, overpressured and mechanically weak material. We identify sharp lateral variations in pore pressure, which reflect focused fluid flow along thrust faults and have a fundamental influence on the distribution of mechanical properties and frictional stability along the subduction fault. We then use high-resolution data-derived mechanical properties to underpin rate–state friction models of slow slip. These models show that shallow subduction fault rocks must be nearly velocity neutral to generate shallow frictional slow slip. Our results have implications for understanding fault-loading processes and slow transient fault slip along megathrust faults.

最近的大地测量研究表明，俯冲断层可能发生慢滑事件，包括它们的浅层（<15 公里深度）也产生海啸的部分。尽管对此类事件的观察现在很普遍，但对促进浅层慢滑事件的物理条件仍然知之甚少。在这里，我们使用来自中部 Hikurangi（新西兰）俯冲边缘的受控源地震数据的全波形反演来限制慢滑动区域的物理条件。我们发现俯冲断层具有柔顺、超压和机械弱材料的特点。我们确定了孔隙压力的急剧横向变化，这反映了沿逆冲断层的集中流体流动，并对沿俯冲断层的力学特性和摩擦稳定性的分布产生了根本性影响。然后，我们使用高分辨率数据衍生的机械性能来支持慢滑的速率状态摩擦模型。这些模型表明，浅层俯冲断层岩必须接近速度中性才能产生浅层摩擦慢滑动。我们的结果对理解断层加载过程和沿大逆冲断层的缓慢瞬态断层滑动具有重要意义。