Abstract

Computerized X-ray tomography applied to analog sandbox experiments performed in a normal gravity field makes possible the analysis of the kinematic evolution, as well as the three-dimensional geometry, of models that simulate tectonic deformations. Most of the plastic or viscous analog materials generally used in a normal gravity field for such models have X-ray attenuations compatible with medical scanner images. Models using soft, cohesionless granular materials were studied. Faults in granular materials corresponding to dilatant zones with lower (by 30%-50%) X-ray attenuation are thus clearly visible in the tomography images. Kinematic analysis was done on imbricate thrust propagation. In materials with an internal friction angle of 30°, thrust propagation is controlled mainly by a triangular pop-up structure resulting from the nucleation of two conjugate thrusts at the basal decollement. The pop-up structure is created immediately in front of the previous thrust. Three-dimensional geometry analysis was tested on lateral ramps parallel to the transport direction. Lateral ramps were induced by changing the frictional boundary conditions at the bottom of the model. Though the lateral ramps strike almost parallel to the transport direction, their dip angle is comparable to the dip angle of frontal ramps.

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