3-D Seismic Imaging of Thrust Fault Evolution and Interaction
Simon Higgins1, Richard J. Davies2, and Benjamin Clarke3
1 Cardiff University, Cardiff, United Kingdom
2 University of Durham, Durham, United Kingdom
3 Statoil, Stavanger, Norway
The mechanisms by which thrust faults initiate, propagate and interact are less well defined than those described in extensional systems. This knowledge-gap has become particularly significant since the advent of deep water exploration of fold and thrust belts on continental margins. We present what we believe to be the first 3D seismic analysis of the along-strike variations of thrust fault geometry and displacement utilising over 3000 km2 of 3D seismic data from the West Niger Delta.
Isolated thrusts within this study area display, asymmetric, bell-shaped displacement profiles. However, the majority of the profiles are complicated by the linkage and interaction of forethrusts and backthrusts along-strike. Fault plane geometry, lateral tip lines and fold shape vary within the zones of linkage. We identify three distinct styles of interaction; compressional ‘antithetic interference zones', sub-thrust underlapping and simple fault intersection. These areas of interaction often occur below structural highs, and therefore traps, within the subsurface despite a summed displacement minimum within the relay zone. Furthermore, any deviations below the ‘ideal' fault displacement profile, both on isolated and linked faults, are partially compensated by increases in fold height. This suggests that the magnitude of fault related folding is not dependent solely on fault slip, as suggested in previous models, instead fold strain compensates for the fault displacement deficit. Our initial results on the controls on fault geometry within linkage zones suggest the mode of lateral propagation as a dominant factor in determining the style of interaction, with some thrust faults initiating within the detachment and others within the overburden.
Understanding lateral thrust propagation, growth history and the evolution of structural highs within relay zones is fundamental for fault seal analysis, particularly within systems predicted as having coincident trap development and hydrocarbon migration.