BOUNDARY-CONDITIONS IN SANDBOX MODELS OF CRUSTAL EXTENSION - AN ANALYSIS USING DISTINCT ELEMENTS

The geometries of faults that form in the brittle hanging wall above large low angle detachments has been an active topic of research in petroleum geology and geophysics for the last decade in order to understand the progressive development of the geologic structures and to identify possible petroleum traps. Experimentalists have used sandbox models to try to gain insight into the kinematics and mechanics of the deformation of overburden above detachments. Although the structures observed in some of the models resemble those observed in nature, boundary conditions and constitutive properties of these models have rarely been measured precisely so the experiments are often difficult to interpret. We use an entirely numerical approach based on the distinct element method (DEM) in which the overburden is represented by hundreds of individual elements that interact mechanically through contact forces. The faults that form in an assemblage of elements resemble those observed in nature. The boundary conditions are prescribed as are the material reactions of individual elements so the numerical experiments are more easily interpreted. We suggest that DEM models complement sandbox models and can be used to interpret the progressive development of geologic structures.