Fluid Pressures, Solute Transport, and Fluid Budgets at Subduction Zones

At subduction zones, tectonic loading of offscraped and underthrust sediments results in rapid compaction and high rates of fluid expulsion. The resulting hydrologic and mechanical systems are intimately linked with one another, and probably change dramatically through time. The potential for devastating earthquakes and tsunamis is strong motivation for understanding how fluid processes may control fault zone strength and material properties. The fate of fluids entering subduction zones is also a key issue in balancing fluid budgets at convergent-plate boundaries, in estimating pore-fluid pressures at depths where earthquakes nucleate, and in controlling the evolution of mechanical strength and structural development. Distributed deformation, relatively high rates of fluid production, active plate boundary faulting, and accessibility to drilling, imaging, and sampling constitute ideal natural laboratory conditions for studying the interplay of fluid flow and tectonics, as well as for evaluating fluid, heat, and solute mass balances. A number of recent studies have highlighted the importance of fluids in subduction zone tectonics, and have improved our understanding of flow pathways. Despite such advances, the answers to many key questions have remained elusive. What are pore fluid pressures and porosities at depths where earthquakes nucleate? Is fluid flow along faults steady through time, or is it transient? If flow is transient, is it related to the seismic cycle?

I investigate geohydrology at convergent plate margins by combining field data collected on Ocean Drilling Program (ODP) cruises, laboratory experiments, and computer models. In the laboratory, I conduct consolidation experiments to learn about sediment mechanical properties, permeability, and pore pressure. These experiments entail squeezing samples collected from active subduction zones at pressures equivalent to 1-3 km of burial. Computer models are an important part of this work, as another type of "experiment" that helps us learn about important processes we can't always observe directly. Field data collected by drilling in ocean trenches yields important information about compaction state and pore water chemistry - powerful constraints for understanding the development of fluid pressure and fluid movement.

Contact: Demian Saffer