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The kinematics and geometry of segment boundaries on normal faults
2014-09, Conneally, John
Normal faults, when observed in detail, are commonly seen to consist of arrays of segments. The geometry of the boundaries between these segments has been extensively studied in outcrop and in subsurface geophysical datasets. Existing models generally consider that at low displacements the segments interact by deformation of the intervening rock volume, and become progressively linked as the displacement increases. The interaction and linkage of these segments is important in the formation and development of fault zones. The recent increase in availability of high quality 3-D seismic reflection data has allowed the detailed geometry of faults to be better imaged. While there are some studies focused on the geometry of segment boundaries, few have focused on the detailed small scale features of these structures and very few studies have focused on the kinematics of these structures. In this project a highly detailed analysis of the geometry and kinematics of segmented normal faults imaged in high quality 3-D seismic reflection data has been carried out. This analysis has revealed substantial departures from the relatively simple geometries and evolutionary models which are generally inferred from 2-D or lower resolution 3-D mapping. These departures include:- the formation of an array of parallel faults which become an array of interacting segments by the localisation of displacement onto shorter lengths of the established fault surfaces; the formation of a segment boundary by the propagation of a splay from a preexisting through going fault; the removal of large scale asperities and also stepping during lateral propagation of a fault giving rise to a segmented geometry. Adjustments to the existing models and a classification scheme for segment boundaries based on their 3-D geometry are proposed. Despite the observed variability in the nature of segment boundaries, all of the structures examined in this thesis formed in a way which was geometrically and kinematically coherent throughout their development and evidence for the development of segment boundaries by the coalescence of initially isolated faults has not been found. In each case, combining displacements accommodated by discontinuous (faulting) and continuous (folding) deformation yielded simple overall displacement distributions associated with a single structure. Kinematic analysis demonstrates that faulting and folding show, not only spatially complementary variations, but also, that these components are complementary in time. During the development of a segmented fault array segment boundaries are the areas where continuous deformation is most prevalent.