Seismogenic fault fracturing can create considerable fracture permeability in and around fault zones initiating large fluxes of fluid, particularly at fault terminations and dilatational jogs. In this work we show that fluids can also be channeled and potentially mixed through a network of interconnected high-angle microfractures generated by transient stress perturbations associated with a passing earthquake rupture. By using the orientation, chemical composition, and salinity in ca. 200 fluid inclusions trapped in healed microfractures across the damage zone of a crustal-scale fault, we show that high-angle healed microfractures close to the damage zone/fault core boundary host high CO, contents and a wide range of salinities. The width of this zone is 35 m. The high angle microfractures are interpreted as having formed from the passage of earthquake ruptures as they are consistent with the inferred stress field from dynamic rupture models. We infer that the rapid creation of the fracture network leads to phase separation and fluid mixing, resulting in the highly variable fluid chemistry. The results suggest pore-fluid flow fluctuations are not only restricted to geometrical irregularities along faults, but also to regions of the damage zone close to a passing earthquake.