ADDING STRUCTURES TO 3-D GEOLOGIC MAPS

Combining geologic maps and cross-sections into traditional block diagrams is a time-tested and effective way to portray the structure of a region and to illustrate how maps and cross-sections work together; block diagrams are especially valuable for non-specialists. The inherent power of block diagrams is dramatically increased by software that can create interactive 3-D models of a region, which can be rotated, panned, and zoomed by the user. Particularly useful software options include Midland Valley’s MOVE 2010 powerful modeling package, ESRI’s GIS-based applications, Google Earth, and Google SketchUp. The best way to create virtual block diagrams is to combine the individual strengths of two or more applications, and merge the results into a single 3-D model.

The most effective 3-D models drape geologic maps on topography and show how the maps and cross-sections connect at the topographic surface. Creating models in segments gives the user flexibility to ‘turn off’ individual portions of the surface to sequentially reveal multiple cross-sections. Such models help students and non-specialists visualize geologic structures, and provide geologists with a valuable tool for assessing the validity of geologic interpretations.

Even the best 3-D virtual block diagrams can be challenging for a non-specialist to interpret and understand. Basic concepts such as bedding and strike and dip are unfamiliar to most non-geologists. Adding structures and textures to geologic maps can clarify these fundamental concepts. For example, ArcGlobe can portray the strike and dip of bedding of different units as color-coded 3-D ‘wafers’ that protrude above the surface and are precisely oriented to match the orientation of beds. Structures such as plunging folds become readily apparent using this technique.

Another approach is to use the astonishing flexibility and power of Google SketchUp to accurately model geologic structures in real-world coordinates and export the results to either Google Earth or ArcGlobe. These accurately constructed and located models of geologic structures can be integrated with geologic maps, and are particularly effective for showing how bedrock geology affects the topography of a region.