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Numerical dynamic analysis was carried out for a field in the coastal swamp depobelt of the Niger Delta basin using subsurface growth faults mapped by detailed 3D structural interpretation of seismic data. Orientation analysis of the faults provided the necessary fault plane data while the requisite kinematic information, comprising of slip directions and senses of movement on the faults, were respectively extracted from fault surface corrugations and cut-off points of seismic horizons on the faults. This data set was subjected to paleostress inversion using the rotational optimization module of the Win-tensor program. The results show that the faults are basically dip slip faults with only minor lateral components of displacement. More importantly, it reveals the best-fit paleostress tensor, considered to be active during the Upper Miocene, in the coastal swamp depobelt of the basin, to be a purely extensional stress tensor characterized by a maximum horizontal stress (SHmax) oriented NE-SW and a NW-SE principal extension direction. None of the three principal stresses was found to be truly vertical or horizontal.