ANALOG MODELING OF FAULTING PATTERN, DUCTILE DEFORMATION, AND VERTICAL MOTION IN STRIKE-SLIP-FAULT ZONES

The relationship between faulting, ductile deformation, and vertical d isplacement in provinces of strike-slip faults were analyzed using ana logue modeling. The described experiment considered a two-layer, small -scale model for the lithosphere, set on a low-viscosity fluid that al lowed free isostatic compensation. The development of the faults and t heir orientation follow generally Riedel's model, but fault spacing de pends on the thickness of the brittle layer, and lateral displacement of the brittle layer was associated with series of deep, elongated dep ressions that developed along the trace of the principal strike-slip f ault. The depressions correspond to local thinning of the brittle laye r, and the amount of thinning is more than 60% in places. The underlyi ng ductile layer displayed two types of superimposed deformation, name ly a series of tight, parallel folds, occurring on top of elongated do mes. The folds are attributed to the compressive component of the stri ke-slip displacement, and the updoming to the extensional component. T he elongated domes are located beneath the superficial depressions, an d the deeper troughs underlie shallow uplifted structures in the defor med band. Significant vertical motion was observed along faults that a re considered as perfectly strike-slip faults, according to the classi cal Riedel model. The thinning of the brittle layer, and the deep defo rmation of the ductile layer, are in good agreement with actual exampl es of pull-apart basins and elongated swells in large strike-slip zone s. A new structural pattern developed during strike-slip shear is prop osed, relating the geometrical relationships between faults, folds, an d elongated domes to the stress axes.