THE ANALYSIS OF PROGRESSIVE DEFORMATION FROM AN INSCRIBED GRID

The analysis of deformed inscribed grids (or equivalent particle points) from scale-model experiments permits a very detailed investigation of the progressive development of geological structures. Numerical methods to calculate values related to the finite deformation (strain ellipse, finite rotation and displacement) and to the instantaneous deformation rate (velocity, stretching rate, vorticity, kinematical vorticity number, spin) from the co-ordinates of digitized grid nodes are summarized. These values can be plotted directly (e.g. as principal strain axes) or their magnitudes can be contoured across the surface of the model. Particular consideration is given to the practical advantages of separating the overall heterogeneous deformation into an average homogeneous component and an additional heterogeneous component representing deviations away from this standard state. This approach corresponds closely to the concept, commonly used in the analysis of mechanical instability, of a perturbation superimposed on a basic steady flow.