The Effect of Cover Strength on Extensional Fault Propagation

Emma Finch¹, Rob Gawthorpe¹, and Stuart Hardy^2
1 Manchester University, Manchester, United Kingdom
² Universitat de Barcelona, 08028 Barcelona, Spain

A discrete element technique has been developed to investigate the effect of cover strength on the propagation of blind normal faults of varying dip. Slip on the basement fault is initially observed through the growth of an upward-widening monocline in the cover where the width of the monocline increases as fault dip decreases. Increased slip results in the monocline being breached by a single, through-going structure, where strain localises onto a single fault producing hangingwall synclines and footwall anticlines. Fault propagation and folding in the cover are also strongly controlled by the strength of the overburden material. A reduction in the strength of the cover results in: a) the width of the monocline above the fault tip increasing, b) more noticeable footwall thinning and hangingwall thickening of beds and c) a reduction of the rate of fault propagation into the cover. Structures observed from multi-layer experiments demonstrate that the more competent layers dominate basement fault propagation through the overburden, producing complex structural relationships. Faults develop along layer boundaries and are not necessarily linked to the basement fault at depth. Inclusion of syn-tectonic sedimentation results in a marked difference in both the rate and style of fault propagation. As sedimentation rates are increased the time to develop a single through-going structure increases and an increase in the coherence of the sediment reduces the rate of fault propagation.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005