How successful are analogue models in addressing the influence of pre-existing fabrics on rift structure?

Sandbox models have been widely used to investigate normal fault geometries , evolution and propagation. As modelling attempts to investigate more aspe cts of normal faulting, the effects of pre-existing fabrics on normal fault geometry developed within the brittle upper crust have become a topic of i nterest. Analogue models have been developed for oblique rifting and the in fluence of pre-existing fabrics on transfer zone geometry. These models use pre-cut geometries in underlying plates to impose 'pre-existing' fabrics o n the developing normal fault system. However, to really mimic natural syst ems it is the sand itself that should contain the pre-existing fabrics. The problem is that cohesionless sand has no tensile strength, while the influ ence of preexisting fabrics on rift structure in the upper crust attests to the important role played by relatively small variations in rock strength anisotropy caused by pre-existing fabrics. Consequently it is necessary to assess how significant the departures are between model and natural example s and whether a new approach to modelling pre-existing rift structures is r equired. (C) 1999 Elsevier Science Ltd. All rights reserved.