Faults control geological situations on many different scales. Nevertheless their genesis, growth, and slip behaviour under different conditions are often only poorly known, although their kinematics and mechanics are essentially responsible for the structural development of the crust. Technological advances in the recent years have made it possible to explore the sliding behaviour of fault rocks at high, i.e. seismic, slip velocities in the laboratory complementing studies at slow, i.e. nucleation, sliding velocities. At the same time advanced geo-monitoring has allowed us to observe natural sliding phenomena that cover a broad range of slip velocities and extend into parts of the lithosphere that were previously thought to flow aseismically, such as slow slip events and tremors. These new observations document the complexity of displacement accommodation along fault zones and call for a re-assessment of the simple seismic-aseismic classification. Furthermore, increased imaging possibilities show that local grain size reduction to nano-grains, disintegration into amorphous material and melting occurs in many natural fault rocks and in lab-produced gouges, under a wide range of slip velocities. The understanding of the underlying physical processes that lead to the production of nano-grains, amorphous materials and melts, together with their strain-rate sensitivity, are of crucial importance to better constrain the rheological behaviour of fault zones.

Bridging the temporal and spatial gap between experimental and natural faults remains a challenge. We invite experimental, field and geophysical studies that address fault growth, slip behaviour and its microstructural record using a broad spectrum of geoscience sub-disciplines, including seismics, experiments, analogue and numerical modelling, outcrop analysis, and theoretical considerations. A key question is how to tackle the temporal, spatial and geometrical scaling of laboratory results to natural faults.