USING CLOSE-RANGE PHOTOGRAMMETRY TO ANALYZE PHYSICAL MODELS OF BASEMENT UPLIFTS

Physical models have been widely used to study geological structures for more than one hundred years. The greatest benefit of physical models is that with proper scaling of model dimensions and materials, researchers can directly observe structural or tectonic processes that take millions of years to occur naturally. Despite this benefit, however, use of physical models is not widespread because their construction and analysis is commonly labor-intensive work that yields largely qualitative information on structural geometry and limited quantitative information on displacement and strain. Some of these difficulties can be overcome by using close-range photogrammetry to obtain quantitative information on the geometry, displacement, and strain patterns in an evolving physical model. The technique is an inexpensive, high-resolution, non-invasive, and efficient method that uses standard commercial software and a digital camera to determine the (x, y, z) positions of high-contrast markers placed on the model surface. The model geometry at any given time is defined by the positions of all the markers, whereas strain and displacement are obtained by comparing or tracking the positions of the markers at different times during an experiment. To demonstrate the versatility and power of the technique, we conducted a close-range photogrammetric analysis of two scaled physical models of monoclines that form above basement-involved reverse faults with differing displacement distributions. Comparison of the models allowed us to link fault displacement and lateral propagation history to unique, evolving, 3-D geometries, cover rock displacement, and deformation patterns that are unlikely to be revealed by other physical modeling techniques. These links may allow us to interpret in natural settings, the growth history or displacement patterns of poorly imaged faults that underlie basement uplifts, or to predict the pattern of smaller-scale deformation that might occur within a basement-involved fault-related fold.