Analogue modeling of faulting pattern, ductile deformation, and vertical motion in strike-slip fault zones

The relationship between faulting, ductile deformation, and vertical displacement in provinces of strike-slip faults were analyzed using analogue modeling. The described experiment considered a two-layer, small-scale model for the lithosphere, set on a low-viscosity fluid that allowed free isostatic compensation. The development of the faults and their orientation follow generally Riedel's model, but fault spacing depends on the thickness of the brittle layer, and lateral displacement of the brittle layer was associated with series of deep, elongated depressions that developed along the trace of the principal strike-slip fault. The depressions correspond to local thinning of the brittle layer, and the amount of thinning is more than 60% in places. The underlying ductile layer displayed two types of superimposed deformation, namely a series of tight, parallel folds, occurring on top of elongated domes. The folds are attributed to the compressive component of the strike-slip displacement, and the updoming to the extensional component. The elongated domes are located beneath the superficial depressions, and the deeper troughs underlie shallow uplifted structures in the deformed band. Significant vertical motion was observed along faults that are considered as perfectly strike-slip faults, according to the classical Riedel model. The thinning of the brittle layer, and the deep deformation of the ductile layer, are in good agreement with actual examples of pull-apart basins and elongated swells in large strike-slip zones. A new structural pattern developed during strike-slip shear is proposed, relating the geometrical relationships between faults, folds, and elongated domes to the stress axes.