Quantitative analysis and visualization of nonplanar fault surfaces using terrestrial laser scanning (LIDAR) – The Arkitsa fault, central Greece, as a case study
Many fault surfaces are noticeably nonplanar, often containing irregular asperities and more regular corrugations and open warping. Terrestrial laser scanning (light detection and ranging, LIDAR) is a powerful and versatile tool that is highly suitable for acquisition of very detailed, precise measurements of slip-surface geometry from well-exposed faults. Quantitative analysis of the LIDAR data, combined with three-dimensional visualization software, allows the spatial variation in various geometrical properties across the fault surface to be clearly shown. Plotting the variation in distance of points from the mean fault plane is an effective way to identify culminations and depressions on the fault surface. Plots showing the spatial variation of surface orientation are useful in highlighting corrugations and warps of different wavelengths, as well as cross faults and fault bifurcations. Analysis of different curvature properties, including normal and Gaussian curvature, provides the best plots for quantitative measurements of the geometry of corrugations and folds. However, curvature analysis is highly scale dependent, so requires careful filtering and smoothing of the data to be able to analyze structures at a given wavelength.
Three well-exposed fault panels from the Arkitsa fault zone in central Greece were scanned and analyzed in detail. Each panel is markedly nonplanar, and shows significant variation in surface orientation, with spreads of ~2025 in strike and 10 in dip. Most of the variation in orientation reflects decimeter- and meter-scale corrugations and longer wavelength warps of the fault panels. Average wavelengths of corrugations measured on two of the panels are 4.04 m and 4.43 m. Whereas the orientations of the three fault surfaces show significant variations, the orientations of fault striae are very similar between the panels, and are tightly clustered within each panel. Fault-slip analysis from each panel shows that the local stress field is consistent with the regional velocity field derived from global positioning system data. The oblique slip lineations observed on the fault panels represent a combination of two contemporaneous strain components: north-northeastsouth-southwest extension across the Gulf of Evia and sinistral strike slip along the west-northwesteast-southeast Arkitsa fault zone.