In ductile deformation, important progress has been made toward understanding rheological properties under deep mantle conditions. These studies provide important insights into the dynamics of the Earth's deep interior. In addition, significant progress has been made toward understanding the role of chemical environment on rheology and the influence of microstructures such as grain-size. In the brittle field, important advances were made in the observation of the spatio-temporal evolution of faulting. The complex interplay of microcracking, crystal plasticity, diffusive mass transfer and pore collapse in controlling the brittle-plastic transition under crustal conditions have been elucidated.
Recent investigations demonstrate the importance of fluid flow on frictional strength.
New measurements have clarified the influence of normal stress, temperature and mineralogy on friction constitutive behavior. Some of these experimental observations are being incorporated into crustal faulting models that provide physical insights into the dynamics of the earthquake cycle.