Development of strike-slip faults: shear experiments in granular materials and clay using a new technique
A new experimental technique has been developed to study fault development in layers of moist granular materials (clay and fault gouge) in shear. Faults nucleated on pre-existing pores and on low-displacement protofaults in flaw-free areas. Only a small number of the protofaults developed significant displacement, forming conjugate simple fault sets. After nucleation, simple faults propagated in-plane. As these simple faults grew in length and new simple fault sets nucleated, they began to interact and coalesce. Simple faults linked up to form compound faults, and compound faults linked up to form even larger through-going strike-slip faults. The fault patterns produced in the shear experiments were integrated fault networks consisting of several sets of conjugate shears and tensile structures. Compound faults exhibited both releasing and restraining steps formed during fault coalescence. Displacement along such a compound strike-slip fault caused a mismatch of the two walls. A few points became resistant barriers while the remaining segments became pull-apart basins. Both releasing and restraining steps led to the development of pull-apart basins. Fault displacement and propagation rate were linear functions of fault length. The difference between the experiment described here and traditional Riedel experiments is that the new experiments do not have a pre-existing fault in the experimental setup. Therefore they are more suitable to study fault nucleation and evolution in a broad shear zone.