Fault-related deformation results in zones with contrasting fluid flow properties to the surrounding country rock. These zones exert significant controls upon the migration of fluids in the brittle crust. It is clear that fluids in fault zones influence earthquake processes over a variety of timescales. Coseismic processes such as dynamic triggering of earthquakes and aftershocks, triggering by pore pressure diffusion, and dynamic fault weakening mechanisms are affected by fluids and pore pressures. Over the timescale of the seismic cycle, fault instability can be promoted by the build up of pore pressure and fluid-assisted alteration or cementation may change fault rock mechanical properties between earthquakes. The key parameter that determines how, when and where fluids migrate within fault zones is permeability. Throughout the duration of activity on a particular fault, permeability can be created through fracturing or dilatant cataclasis, reduced through cementation, or re-distributed as displacement occurs. In this session we will examine the feedbacks that exist between deformation processes and fluid migration that are integral to understanding the earthquake source. We aim to gather contributions based on seismic data, geological observations, experimental results and hydro-mechanical modelling of faulted environments to discuss the interactions between seismic processes and fluid migration.