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Title: Control of fault geometry, interaction and mechanical stratigraphy on strain distribution in normal fault zones
Author: Lapadat, Ioan Alexandru
ISNI:       0000 0004 7653 683X
Awarding Body: Durham University
Current Institution: Durham University
Date of Award: 2017
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It is known that the development and distribution of strain associated with normal faulting is influenced by the process of fault growth within mechanically layered and heterogeneous sedimentary rocks. Fault displacement is often partitioned between discontinuous throw on slip surfaces and zones of distributed strain, which in some cases can be the result of folding associated with normal faulting. The amount of ductile deformation can vary significantly along the strike of a normal fault array as a result of various processes, such as fault-tip propagation and fault interaction and linkage. In this study we investigate the influence of mechanical stratigraphy, fault geometry and fault mechanical interaction on the variability and distribution of ductile strain in the rock volume surrounding normal faults. We show that mechanical competence contrasts can control the manner in which strain is accommodated and, hence the overall patterns of secondary fault and fracture systems within normal fault-related folds. This can have consequences on the way in which disruption of an associated shale smear occurs, impacting the sealing properties of the fault zones. Also, we show that folding can be generated by different mechanisms that vary in importance in time and space along a normal fault array. Mechanical properties of the host rocks, together with the spatial configuration of the faults control the mechanical interaction between faults, exerting an influence on the variability of ductile strain within the volume of deformation surrounding normal faults. Specifically, conjugate normal faults that intersect within layers with low compressibility have geomechanical characteristics favorable for migration of stress concentrations near the upper fault tips which generate higher propagation/slip ratios and the development of lower amplitude folds, or no folding. The host rock lithology and the overlapping normal fault configuration at the time of interaction controls the three-dimensional relay ramp geometries and associated strains within relay ramps. Normal faults within mechanically competent rocks tend to develop relay ramps with tabular geometries, that have larger aspect ratios and smaller fault-parallel shear strains compared to those developed in mechanically incompetent rocks. Fault-normal shear strain within ramps can be the result of the development of asymmetric displacement gradients on the overlapping faults as a result of mechanical interaction between surface-breaking normal faults. The probability of a relay ramp bounded by surface-breaking normal faults to be completely breached depends not only on the accumulated ramp shear strains and the ratio between throw and separation of the bounding faults, but also on how the throw is partitioned between the interacting faults. Also, we argue that the style of breaching, dominantly through the upper part of the relay ramps, is influenced by the stress interaction between the overlapping faults and the Earth's free surface.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available