Growing Faults in the Lab: Insights Into the Scale Dependence of the Fault Zone Evolution Process

Analog sandbox experiments are a widely used method to investigate tectonic processes that cannot be resolved from natural data alone, such as strain localization and the formation of fault zones. Despite this, it is still unclear to which extent the dynamics of strain localization and fault zone formation seen in sandbox experiments can be extrapolated to a natural prototype. Of paramount importance for dynamic similarity is the proper scaling of the work required to create the fault system, W-prop. Using analog sandbox experiments of strike-slip deformation, we show W-prop to scale approximately with the square of the fault system length, l, which is consistent with the theory of fault growth in nature. Through quantitative measurements of both W-prop and strain distribution we are able to show that W-prop is mainly spent on diffuse deformation prior to localization, which we therefore regard as analogous to distributed deformation on small-scale faults below seismic resolution in natural fault networks. Finally, we compare our data to estimates of the work consumed by natural fault zones to verify that analog sandbox experiments scale properly with respect to energy, that is, that they scale truly dynamically.