Growth and Interactions of Subparallel Strike-Slip Faults in Post-Messinian Sediments, Levant Basin, Offshore Israel

Abstract

Fault growth and their interactions play a significant role to the formation of pathways for hydrocarbons migration, reservoir permeability and fracking. However, studies of the growth and interaction of naturally occurring strike-slip faults are limited by the difficulty in evaluating the variability of slip across the fault plane. The Levant Basin post-Messinian interval serves us as a ‘box model’ for faults growth and interaction kinematics studies, being a relatively rapidly deforming finely layered brittle interval overlaying the ductile Messinian evaporitic interval and well imaged on 3D seismic data. Here we present a 3D seismic interpretation based study of two overlapping sub-parallel predominantly strike-slip faults in the SE Levant Basin with duplex development between them, as a result of minor faults formation. Direct evaluation of the horizontal slip along segments of these faults is obtained through measurement of offsets on multiple avulsion channel packages crossed by the faults, aided by microscale fault interpretation, seismic attribute analysis and spectral decomposition. In conjunction, the dip-slip components of net-slip along the same fault segments were evaluated by measuring the offset of seismic interpretation horizons across these faults. Results display linear relationships between the dip-slip and the strike-slip, with the dip-slip constituting ~15% of the net-slip. These results corroborate that the two components developed simultaneously and dip-slip is not a product of fault reactivation. Moreover, the linear relations imply that the measured dip-slip offsets, which are readily measurable, can serve as proxies for evaluating the predominant strike-slip across these faults. Thus, the dip-slip component of the offsets across the faults were measured on multiple interpretation horizons and used to produce continuous displacement maps of the fault planes, which we consider to represent net-slip across each major overlapping fault. Findings show that breaching occurs progressively within the overlap zone due to faults interactions, with secondary faults initiation equally from the major faults on each of the sides. The secondary faults merge within the zone and develop a sigmoidal duplex. The duplex forms horst, graben and half-graben structures, indicating the prevalence of dilatational strain conditions. Additionally, duplex formation exhibit hierarchical growth in plain view, with inward minor fault formation from the boundaries of the major fault tips towards the center of the overlapping zone. Displacement maps of the major faults planes reveal highly segmented complex spatial patterns, with continuous segments observed in both the breached and the intact parts of the overlap zone. Analysis of displacement-distance plots show that areas of minor faults initiation in many cases coincide with the location of the initial paleo-tips of the fault segments. Moreover, the displacement profiles of each segment suggest that most of them formed after the sediment deposition, and propagated radially during their growth. Additionally, segment complexity increases near the Top-Evaporites surface. Some of the segments appear to have nucleated close to the Top Evaporites horizon and likely propagate upward. The proposed methodology of identifying dip-slip and strike-slip relationships from 3D seismic data, can be used to: i) differentiate simultaneous from reactivated slip ii) distinguish strike-slip or dip-slip dominated segments; ii) examine weakness zones within strike-slip dominate faulting regimes. Furthermore, our detailed study show that minor faults of the duplex initiate at the paleo-tips of linked segments of the major faults, likely due to stress concentration

AAPG Datapages/Search and Discovery Article #90341 ©2019 AAPG Geoscience Technology Workshop, Exploration and Development of Siliciclastic and Carbonate Reservoirs in the Eastern Mediterranean, Tel Aviv, Israel, February 26-27, 2019