The Effect of Cover Strength on Extensional Fault
Propagation
Emma Finch1, Rob Gawthorpe1, and Stuart
Hardy2
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