Comprehensive fracture assessment is not an easy task as most fracture analyses rely on two-dimensional outcrops. A newly developed acquisition system of full resolution 3D Ground Penetrating Radar (GPR) and subsequent migration of the data allow, for the first time, to image fracture and deformation band networks in three dimensions. A full resolution GPR data set was acquired in the Madonna della Mazza quarry in the Maiella mountains, Italy. The quarry is cut into the Upper Cretaceous (Maastrichtian) Orfento Formation in the limb of an anticline. Combining 3D GPR and outcrop analysis reveals both the sedimentology and fracture characteristics in the quarry. The GPR data images the strata in more detail than what is visible in the quarry walls. For example, GPR data reveal a series of prograding bedsets that are interpreted as sub-aqueous dunes resulting from a unidirectional bottom or tidal current in the outer ramp environment. A fine-grained carbonate, lithofacies B, appears intermittently throughout the whole strata. In the massive grainstone beds extensive bioturbation destroyed the sedimentary structure and prevents the interpretation of the depositional process. The fracture development in the quarry is partly stratigraphically controlled. Deformation bands preferentially occur in the high porosity and high permeability massive grainstone unit, while stylolites are extensively developed in the thin-bedded packstone-grainstone lithofacies. The fracture analysis in the GPR data corroborates results of the outcrop analysis of previous workers. Performing a manual interpretation of the GPR data, faults with two dominant orientations (N-NW and E-W) were identified. The automated "Ant Tracking" analysis of the GPR data, however, revealed four dominant fracture orientations (N-NW, NW, W-NW, and EW). Furthermore, the automated ("Ant Tracking") 3D GPR analysis reveals a mechanical unit boundary; lithofacies C contains almost twice the density of deformation bands as the strata below. Integrating the outcrop analysis with the automated analysis of the 3D GPR data using "Ant Tracking" is essential for accurately quantifying the entire fracture population in the quarry. Total fracture diversity and abundance has previously been underestimated by 2D outcrop mapping and is also not completely depicted using manual interpretation of 3D GPR data.

Our current understanding of thrust fault kinematics predicts that thrust faults nucleate on low angle, weak surfaces before they propagate upward and forms a higher angle ramp. While this classic kinematic and geometric model serves well in some settings, it does not fully consider the observations of footwall deformation beneath some thrust faults. We examine an alternative end-member model of thrust fault formation called “ramp-first” fault formation. This model hypothesizes that in mechanically layered rocks, thrust ramps nucleate in the structurally strong units, and that faults can propagate both upward and downward into weaker units forming folds at both fault tips. To explore this model, we integrate traditional structural geology field methods, two dimensional cross section reconstructions, and finite element modeling. Field data and retro-deformable cross sections suggest that thrust faults at the Ketobe Knob, in Utah nucleated in strong layers and propagated upward and downward creating folds in weak layers. These findings support the hypothesis that thrust faults and associated folds at the Ketobe Knob developed in accordance with the ramp-first kinematic model.We can apply this understanding of the mechanics behind thrust fault nucleation and propagation in mechanically layered stratigraphy to a wide range of geological disciplines like structural geology and tectonics, seismology, and petroleum geology. By incorporating our knowledge of lithology into fault models, geologists are more likely to correctly interpret structures with limited data sets.

The ENE-trending Himalayan fold-thrust belt in Pakistan exhibits contrasting deformation styles both along and across the strike. The centrifuge modelling technique has been used to investigate these variations in structural style. For the purpose of modelling, the Salt Range and Potwar Plateau (SR/PP) stratigraphy has been grouped into four mechanical units. From bottom to top these are the Salt Range Formation, carapace unit (Cambrian-Eocene platform sequences), Rawalpindi Group, and Siwalik Group. These stratigraphic units of alternating competence, composed of thin layers of plasticine modelling clay and silicone putty, rest on a rigid base plate that represents the crystalline basement of the Indian plate. The models are built at a linear scale ratio of ~10-6 (1mm=1km) and deformed in a centrifuge at 4000g. The models are subjected to horizontal shortening by collapse and lateral spreading of a “hinterland wedge” which simulates overriding by the Himalayan orogen (above the Main Boundary Thrust). The models of the central SR/PP show that the accretionary wedge develops a prominent culmination structure with fault-bend fold geometry over the frontal ramp, while the eastern SR/PP is more internally deformed by detachment folds, fault-propagation folds and pop-up and pop-down structures. Model results show that the transition from fault-bend fold to detachment-fold and fault-propagation-fold geometry in the prototype may take place in a transfer zone marked by an S-bend structure (Chambal Ridge and Jogi Tilla) at the surface and the lateral ramp in the subsurface. Moreover, the models suggest that an oblique ramp below the Kalabagh strike-slip connecting the two frontal ramps below the Surghar Range and the central Salt Range developed similar structure that can be observed in the prototype. The model results also show that the Northern Potwar Deformed Zone may have been developed over ductile substrata due to the close similarity between the models and the prototype structures. The deformation style in the models illustrates the importance of mechanical stratigraphic and basement ramp systems in the evolution and the structural styles of the SR/PP. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2010-07-29 19:42:25.027