Integration of flower structures in strike-slip fault damage zones classification – examples from the West-Congo belt and foreland

Abstract

Damage zones around strike-slip faults constitutes important site of earthquake initiation, propagation, rupture or barrier. They also constitute important sites that host and conduct fluids. Most investigations of these strike-slip damage zones focus on plan view geometries and little attention is paid to subsurface or profile geometries associated. Depending on the presence of a shortening or extensional component during deformation, strike-slip faults do not often show straight path in cross-section. Understanding the expression of damage zones in cross-section is therefore important in predicting subsurface strike-slip faults features. The Paleozoic red feldspathic sandstones of the Inkisi Group in the foreland of the West-Congo Belt show beautiful examples of strike-slip faults with damage zones in both the Republic of Congo and the Democratic Republic of Congo (Nkodia et al., 2020). These strike-slip faults are organized in two major faults system developed in a pure strike-slip regime. The oldest system is dominated by NNW–SSE trending sinistral strike-slip faults and minor E–W striking dextral strike-slip faults. The youngest system consists of dominant NE–SW trending dextral strike-slip faults and minor NW–SE trending sinistral strike-slip faults. Field investigation show four arrangement of flowers structures along the strike-slip faults: (i) those associated with wall damage zones; (ii) those associated with linking damage zones; (iii) those associated with tip damage zones; and (iv) “hourglass” flower structures. Further investigation of strike-slip faults in the Schisto-calaire Group of the West-Congo Belt show also similar flower structures arrangement in limestones. In the Inkisi Group, these arrangements are dependent on the fault growth and propagation. Both strike-slip faults system in the Inkisi Group show an evolving pattern, from closely spaced short faults segments, to highly spaced long faults segments with few interactions of pattern.