Digital Structural Mapping: the end of life as we know it
K.J.W. McCaffrey, R.E. Holdsworth, R.W. Wilson & R.R. Jones*
Reactivation Research Group, Department of Geological Sciences, University of Durham, DH1 3LE, *CognIT a.s. P.B. 610 Busterud, N-1754 Halden, Norway
k.j.w.mccaffrey@durham.ac.uk
Digital structural mapping (DSM) methods involve the acquisition of field data on hand-held computers operating Geographical Information Systems (GIS) software. By connecting to a GPS receiver, geospatial control on observations is automatically provided. With technology advancing rapidly, driven by applications in the engineering, construction and environmental monitoring industries, digital field mapping systems are now becoming affordable and can attain equivalent or better positional performance than is routinely achieved by traditional methods (compass clinometer, etc). For the field structural geologist there are a number of obvious advantages. Powerful multi-attribute mapping and high-resolution spatial analysis can be carried out during fieldwork. The ability to view and analyze data collected at each stage allows an iterative approach to be taken to structural problem solving. Field data may be directly imported to 3-D visualization, analysis and 4-D modeling packages, which can provide further constraints on the viability of the interpretation. Digital formats ensure that the ‘field to publication’ process is more streamlined. We present two case studies that utilize these techniques and illustrate the flexibility and power of the new methodologies for both research and teaching.
A goal of the NERC Ocean Margins thematic programme is to determine the controls on the structural architecture of passive margins. The reactivation of basement faults during passive margin development is often assumed but rarely demonstrated. The NE Atlantic margin contains examples of basement faults suspected of being involved in basin development and also near-offshore basins that are thought to have been influenced by reactivation of basement faults. A database of fault attributes (displacement, spacing, length connectivity) for exposed basement faults is being generated with the aim of developing diagnostic tests for basement reactivation both onshore and offshore. In order to improve the speed of data acquisition and efficiency of its analysis, a DSM system is being developed by Durham RRG (e.g. see Wilson et al. this volume). The GIS platform enables the semi-automated analysis of fault attributes and their temporal and spatial evolution. We can also more readily integrate offshore seismic and subsidence data with onshore basement fault attributes in a GIS platform and address the different scales of observation and the types of data that are acquired in both settings.
In the GEES-funded Assynt 3-D visualization project, we used DSM to construct a 3-D computer model of the foreland region to the Moine Thrust Zone and introduced it as a teaching resource in an undergraduate field mapping class. During mapping training, students often have difficulty with visualizing how structures interact with topography to give outcrop patterns, how structures intersect above or below the surface and how to scale observations from a single outcrop to the map scale. The model was created by supplementing existing field data with new GPS-determined contact locations. The geological boundaries were then ‘draped’ onto a digital elevation model and displayed in 3-D. The models greatly aided the students’ understanding map patterns, the overall 3-D structure and provided a regional context for their mapping.