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We use both analogue and numerical experiments to study the inversion by shortening of a symmetric sedimentary basin. The combination of the two modelling techniques uses the strengths of each method to provide insight into basin-inversion processes. The experiments start with a pre-existing basin filled, in part, with weak layers simulating weak sedimentary rocks. Both footwall and hanging wall can deform freely. The physical properties of the materials used in the analogue experiments (sand and microbeads) and the numerical experiments are appropriately scaled to represent upper crustal rocks. We present a systematic study of the effects of basin infill, basin width and basin location and a sensitivity analysis to understand the effects of the boundary conditions. The results of both methods show that the graben fill accommodates most shortening. Weak layers play an important role in localising shortening with limited reactivation of pre-existing (but weakened) faults. In general, forward thrusts and back thrusts nucleate at the lateral contrast of strong and weak materials and cut across the graben-bounding faults. Weak basal detachments are required to transfer shortening to the basin region. The overall evolution of the analogue and numerical models is encouragingly similar.

The aim of analogue model experiments in geology is to simulate structures in nature under specific imposed boundary conditions using materials whose rheological properties are similar to those of rocks in nature. In the late 1980s, X-ray computed tomography (CT) was first applied to the analysis of such models. In early studies only a limited number of cross-sectional slices could be recorded because of the time involved in CT data acquisition, the long cooling periods for the X-ray source and computational capacity. Technological improvements presently allow an almost unlimited number of closely spaced serial cross-sections to be acquired and calculated. Computer visualization software allows a full 3D analysis of every recorded stage. Such analyses are especially valuable when trying to understand complex geological structures, commonly with lateral changes in 3D geometry. Periodic acquisition of volumetric data sets in the course of the experiment makes it possible to carry out a 4D analysis of the model, i.e. 3D analysis through time. Examples are shown of 4D analysis of analogue models that tested the influence of lateral rheological changes on the structures obtained in contractional and extensional settings.Supplementary material: The nineteen movies referred to in the article are available at https://doi.org/10.6084/m9.figshare.c.4788519