Tectonic fault zones are inherently complex systems, rarely conforming to simplistic or homogenous structural models. They are instead characterized by complex fault geometries, spatially and temporally variable frictional properties, and heterogeneous material properties. This session aims to showcase recent interdisciplinary advances that quantify how fault zone complexity influences earthquake nucleation, rupture propagation, termination, and post-seismic deformation. We welcome contributions that utilize a broad range of approaches, including geodetic measurements of fault creep and slow-slip, in-situ field experiments, and seismic field observations. Submissions employing laboratory experiments, theoretical analyses, and numerical modeling are encouraged, particularly those that focus on understanding how frictional properties, fault geometry, material properties, and fault roughness control earthquake rupture processes. We also encourage work that bridges spatial and temporal scales or integrates multiple datasets to provide a more holistic view of fault system behavior.