A 3-D EARTH MODEL OF THE FALL CREEK AREA, SEVIER THRUST BELT, EASTERN IDAHO

We created a 3-D earth model of the Fall Creek area in the Sevier thrust belt of eastern Idaho using EarthVision® software. The objectives of this research were to determine subsurface geometries in this part of the thrust belt, evaluate the use of geologic maps as model inputs, and to develop methods to achieve accurate results. The model inputs consisted of contact locations and attitudes from a published geologic map. Using only a geologic map as input challenges the modeler to interpret subsurface geometries in a geologically reasonable manner that also matches the surface data. Steps in the modeling method included georeferencing the geologic map, extracting contacts and faults from the map, and creating a conceptual cross-section to guide modeling. Attitudes from the map were used to project faults and strata to depth, and unit (formation) thicknesses were calculated from the map. One horizon was selected as a reference to create the basic shapes of folds, and the other units were created by adding or subtracting from that horizon while maintaining true stratigraphic thickness. This process was iterated until an exact match was obtained with the geologic map. Achieving a good match required weeks of modifying and testing unit thicknesses, and revealed that map-scale variations in dip and thickness require a disproportionate amount of time to model when using the thickness method of creating stratigraphic units. The topography was defined in the model as an unconformity to properly truncate the stratigraphic units. The 3-D model allows quick volume calculations for resource evaluation.