AAPG Geoscience Technology Workshop

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Evolution of Normal Faults: Displacement Patterns in 3-D Seismic From the Eastern Levant Basin


The continental shelf offshore Israel is densely populated by slump units in the Pliocene -Pleistocene section. The gigantic unit known as the Israel Slump Complex (ISC) and its overburden are incised by thin-skinned fault systems. Quantitative fault displacement analysis presents the relation between the slump units and the evolution of normal faults incising them. Following structural standard interpretation, slump units and an array of normal faults and are mapped in the Gabriella seismic volume, a high-resolution 3D seismic survey (depth-migrated) located 12 km offshore Netanya. The stratigraphic column of the volume includes the post-Messinian section of Saqiye and Kurkar groups. Fault systems are characterized by unrestricted blind faults and restricted growth faults. The Middle-Late Pleistocene progradational settings make distinguishing the two types of faults a challenge. Fault displacements are analyzed based on ten key horizons using a step-by-step workflow which includes throw-versus-depth profiles, displacement contour diagrams and displacement gradients. Growth stages within the faults are highlighted using expansion indices and restoration models. Combination of these methods proves useful both for growth model classification and accurate fault mapping. Variations in displacement patterns underscore the control of chaotic features, acting to restrict the growing faults. Two main fault zones are identified: Northern Fault Zone (NFZ) and Southern Fault Zone (SFZ), comprised of N-S and NW-SE striking normal faults, respectively. Four sampled faults yield distinguishable types of growth: (1) Blind fault, where both horizontal and vertical tips close gradually; (2) Restricted growth fault initially evolving as a blind fault, associated with an incision into the ISC at 0.51-0.7Ma; (3) Blind Restricted fault, with two zones of high displacements, associated with the incision of a small slump unit; (4) Blind restricted fault, characterized by high displacement gradients at its deeper part. Maximum displacement zones imply the faults nucleated at 600-700m depth. The restricted growth fault is characterized by shallower maximum displacement zone, interpreted to result from a transition from blind to growth propagation. We find that chaotic structures control fault activation, which depends on the spatial relation between the structures. This can result either locally with segmented activation within the fault, or with lateral growth initiation on the entire fault. The linkage between proximity to slump units and growth pattern may lie in the compaction potential of the latter. The research provides empirical evidence for distinguishing a fault growth and blind stages. This can be especially helpful where faults have similar dimensions and ranges of throw values, which result in minor displacement differences. The presented workflow can also be used for illuminating geo-hazards related to fault activation.