Experimental Modeling of Transfer Zones In Listric Normal Fault Systems

Transfer zones are common features in passive margin settings such as the Gulf of Mexico and the Niger Delta, where displacements on adjacent listric normal faults are accommodated by the development of complex secondary fault systems. Two common types of transfer zones are: (1) Convergent: where two main faults dip towards each other, and (2) Divergent: where faults dip away from each other. Analogue clay experiments have been used to model the geometry and evolution of secondary faults in these two end member scenarios. Within each category, three experimental setups have been studied where the two main faults (a) approach one another, (b) are offset by 90 degrees and (c) overlap each other. The different experimental configurations have been achieved by creating indentations along the frontal edges of both the fixed and movable base plates. During extension, master faults formed above the overlying base plates and sets of antithetic faults formed tied to the underlying base plates. The master faults developed by coalescence of a number of synthetic faults, whereas antithetic faults formed a fault zone, made up of evenly-spaced, discrete fault segments. Fault orientations, fault lengths, fault densities and sizes of connected fault clusters varied with type of transfer zone, structural position relative to the offset and total extension. It has been observed that antithetic fault sets in convergent transfer zones and synthetic fault sets in divergent transfer zones are more consistent in orientation and tend to get connected, although connectivity is higher in the former scenario. Synthetic fault sets in convergent transfer zones and antithetic fault sets in divergent transfer zones change orientation although the two sets remain separated. These observations provide us important insights on the kinematic growth of faults, geometry of fault networks and possible fluid migration pathways within transfer zones.