Surface mapping, structural modelling and kinematics along the sinistral strike-slip fault zone, NE Potwar, Pakistan

This research was carried out to understand the nature of strike-slip Jhelum Fault zone and to propose a model for the surface to subsurface deformation pattern. Field data along with satellite images are used to construct the geological map. Moreover, the subsurface model has been proposed using the mechanism of dip-isogons in computer application which connects points of equal inclination or dip on the outer and inner bounding surfaces of a folded layers. The proposed geological map and subsurface model shows that the Jhelum Fault when propagated in the south from Hazara-Kashmir Syntaxis forms a continuous shear zone on surface with some discontinuous exposure of splay faults rather than exposed as continuous discrete break. Likewise, the subsurface cross sections show that deformation along the fault zone is accumulated by splay faults from the main Jhelum Fault, which forms a positive flower structure with steep north-eastward dips, which is characteristics of strike-slip movement along Jhelum Fault Zone. The vertical stratigraphic throw along these faults shows small offsets and little east–west shortening, indicating that the major slip along the fault is strike slip.

Pure Void Space and Fracture Pore Space in Fault-Fractured Zones

Fault-fractured pore space is complex and difficult to predict and evaluate. For a single independent ramp-flat fault-bend fold structure, the pure void space between two fault walls equals the integrated fracture pore spaces within the fault damage zone if it were concentrated on the fault plane. Using an area balancing technique and geometrical relationship, we have developed a two-dimensional (2D) model to calculate the pore space of fractures associated with fault development. The development and distribution of fault detachment voids or fault fracture pore space are controlled by the physical properties of the deforming medium, mechanics of deformation, and geometry of a fault-ramp structure. We demonstrate how concordant or discordant folding of the fault wall rock affects the nature of fault-fracture pore space. The pure void space and fracture pores in the fault zone can be quantitatively described by the following parameters: initial ramp angle and height, overlap ramp length, throw and slipping displacement, stack thickness, curvature and derivation of the angle between bed and fault plane (Rθ), and dip isogons. Rθ reflects the conformity of two opposite fault sections and the folding accordance of two walls, and it is a key element for the development and distribution of fracture pore space in a fault zone. Furthermore, we observed natural outcrops supporting and validating our model assumptions in the foreland fault system, Central China.

Implications of pericline geometries on 3D fold shape analysis, stress distribution and fracture analysis

<p>The characterization of folds is often limited to two-dimensional cross-sectional views where folds are approximated as cylindrical. This enables simplification of fold shape analysis (using principles such as dip isogons, stereographs, tangent diagrams, and Bezier curve analysis), allows for a simplified analysis of the distribution of stress and strain, and enables and the analysis and visualization of folding associated fractures. However, in a heterogenous medium folds have to terminate somewhere, resulting in more complex three-dimensional geometries. In this study, a 3D finite element modeling approach using a Maxwell visco-elastic rheology is utilized to simulate 3D periclinal folds resulting from single layer buckle folding. With respect to fold shape analysis, we use the forward modeled pericline geometries to demonstrate that geometrical attitude data collected for various cross sections and plotted using traditional 2D methods such as stereographs and tangent diagrams may lead to the misinterpretation of the fold shape as conical. In contrast 3D geometric data such as Gaussian curvature can describe and quantify the 3D fold geometry in its entirety. With respect to folding associated fracture analysis, the 3D modeling results show that shear fractures of various orientations in the fold limb, which cannot be intuitively explained by the strain/stress regimes during 2D buckling and require unrealistic boundary conditions, are feasible to occur during a single deformation event during the development of a pericline. In summary, accounting for the true 3D geometry of buckle fold structures will lead to a better classification of folds, a better understanding of the processes and parameters affecting their development, and enable post-folding failure analysis.</p>