GenLab: A MATLAB ®-based program for structural analysis of folds mapped by GPS or seismic methods

Abstract

GenLab is a MATLAB ® code for structural analysis of digitally and seismically mapped horizons based on the geometrical model of the developable surface. This model is chosen because surfaces of this type result from the bending of a non-stretching stratum and because deviation from developable geometry implies that bed stretching during folding has occurred. The model is therefore linked with straining of the horizon and can be used for highlighting regions of deformation expressed by brittle fracturing or ductile deformation. Mathematically, a developable surface is one upon which straight lines (generators) can be drawn, and along these generators the orientations of tangent planes of the surface remain constant. Our method involves treating real geological surfaces as approximations to developable surfaces and determines the generator lines at different points on the surface. At these points we consider strip samples of the surface radiating in different directions and examine the variability of strike and dip within each sample strip. The radial scan-line length parameter is user-defined, and the optimal value can be easily identified by geostatistical analysis of the depth data. The local plunge lines (the approximation to the generatrix of a developable fold) are therefore identified as the direction associated with the least variation of surface attitude, i.e., the most constant strike and dip. The map pattern obtained by analyzing the plunges and trends of plunge lines across an area allows identification of domains where folding accords closely with a developable geometry. Such domains are recognized from straight plunge lines, defining parallel or convergent patterns. According to the model, deviations from these patterns correspond to regions of structural complexity associated with ductile or brittle straining of the surface being analyzed. The plunge-line analysis therefore offers a useful technique with potential for predicting strained zones and automatic fault recognition. GenLab allows the rapid implementation of this analysis and uses the matrix capabilities and contouring functions of MATLAB.