Models of Fault Transfer Zones in Rift Settings: Insights from Laser Scanned Clay Models

Paul, Debapriya; Mitra, Shankar

Transfer zones act as coordinated systems of deformation where the displacement switches from one fault to the next. They are believed to be important locations for the development of hydrocarbon traps in rift basins. Transfer zones in rift basins are classified into convergent, divergent and synthetic, based on the relative dip directions of adjacent faults within the transfer zone. Experimental models were constructed to determine the geometry, evolution, and fault patterns associated with each of these transfer zones having initial approaching, lateral offset and overlapping fault geometries in the basement. The models consisted of a layer of stiff clay representing the basement and a layer of wet clay representing the cover sequence. Laser scanning and 3-D surface modeling were used to determine the map geometry and compare the models with natural structures. The experimental models added more details and showed a few significant differences from the existing conceptual models. Typically, divergent transfer zones are narrower than convergent transfer zones for the same initial basement fault spacing. Initially approaching, lateral offset and overlapping basement fault configurations differed from each other by the degree of interaction of the secondary faults, the amount of overlap between the fault zones and in some cases, the width of the transfer zone. The main faults curve towards each other in convergent transfer zones, away from each other in divergent transfer zones, and in the same direction in synthetic transfer zones. A primary difference with conceptual models is the significant component of extensional fault-propagation folding which substantially controls the shapes of all the transfer zones. The transfer zones are marked by a progressive change in relief from the footwall to the hanging wall, resulting in a saddle-shaped geometry. The hanging walls of the faults are marked by a gentle flexure or rollover into the fault, with the amount of flexure increasing with fault throw away from the fault tip. The geometries and fault patterns of the experimental structures match some of the observations in natural structures in the East African rift system, the Gulf of Suez and the North Sea. They also provide predictive analogs for interpretation of surface and subsurface structures in areas with poor data quality and in the delineation of potential prospects in rift basins.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013