FORWARD 3D MODELING OF COMPLEX FAULT SYSTEMS USING AN ELASTIC BOUNDARY ELEMENT METHOD

Poly3D, a fast 3D boundary element numerical code and Poly3DGUI a graphical user interface, facilitate the forward modeling of multiple mechanically interacting faults with complex 3D tiplines and irregular surface geometries, limited only by data precision and computing power and memory. Poly3D is based on the analytical solution for an angular dislocation in a half space composed of a homogeneous and isotropic linear-elastic material (Comninou & Dunders, 1975). Six angular dislocations are superimposed to define triangular dislocation elements that are combined to model complex 3D fault shapes without gaps or overlaps. Boundary conditions on these elements are either a uniform displacement discontinuity or the traction vector at the element center. Tectonic deformation can be simulated using remote strain boundary conditions. The GUI runs under the Windows operating system on a PC using OpenGL and Open Inventor technologies. The power of the C++ language combined with fast PC graphics cards and gigahertz CPUs enable real-time 3D simulations of the faulting process and stunning visualizations of deformed horizons, slip distributions, and displacement vector and stress tensor fields.

Forward modeling results from three recent studies use a variety of geologic and geophysical data sets to constrain fault geometries and tectonic histories. 1) GPS data on faults and deformed limestone beds within the Carmel formation are used to investigate fault slip distributions and fault interaction for four sets of intersecting normal faults at Chimney Rock, Utah. 2) GPS measurements and a high resolution DEM are used to analyze the 3D geometry of deformed sandstone beds within the upper Esplanade formation in both the hanging and foot wall of a crustal-scale normal fault in the western Grand Canyon, Arizona. 3) Digital orthoquad photographs, digital topographic maps, and GPS field data on sandstone beds of the Frontier formation within the Emigrant Gap anticline, Wyoming, are used to investigate the relationship between fold shape and the underlying thrust fault geometry and slip distribution. In each study the geometric flexibility of Poly3D and the visualization capabilities of Poly3DGUI have led to new insights into the processes of faulting, fault interaction, and fault-related folding.