The permeability of active subduction plate boundary faults

At subduction zones, continuous influx of fluids drives a dynamic system in which fault slip, fluid flow, and advective transport are tightly coupled. Focused Ocean Drilling Program (ODP) and Integrated Ocean Drilling Program (lODP) efforts have enabled detailed investigations into fault zone structure, architecture, frictional properties, in situ pore pressure, and permeability at several subduction margins. This chapter focuses on quantitative constraints on fault zone permeability, its links to observed fault zone architecture, structure, and seismic reflection character, and its variation with depth and effective normal stress; evidence for temporal and spatial variations in permeability and fluid fluxes. It discusses the implications of existing observations for drainage of excess fluid pressure and the transport of heat and solutes. Numerical modeling studies at individual margins have provided constraints on fault zone hydrogeologic properties through detailed analyses relating pore pressure to sediment and fault permeabilities.