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 develop ment in layers of moist granular materials (clay and fault gouge) in s hear. Faults nucleated on pre-existing pores and on low-displacement p rotofaults in flaw-free areas. Only a small number of the protofaults developed significant displacement, forming conjugate simple fault set s. After nucleation, simple faults propagated in-plane. As these simpl e faults grew in length and new simple fault sets nucleated, they bega n to interact and coalesce. Simple faults linked up to form compound f aults, and compound faults linked up to form even larger through-going strike-slip faults. The fault patterns produced in the shear experime nts were integrated fault networks consisting of several sets of conju gate shears and tensile structures. Compound faults exhibited both rel easing and restraining steps formed during fault coalescence. Displace ment 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 step s 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 experime nts is that the new experiments do not have a pre-existing fault in th e experimental setup. Therefore they are more suitable to study fault nucleation and evolution in a broad shear zone. Copyright (C) 1996 Els evier Science Ltd