Abstract - Normal faults are the dominant structures found in
extensional sedimentary basins developed in continental
rifts and passive margins. The geometry
and growth of faults are intimately linked, and
much of our understanding of how faults grow is
derived directly from observations of fault geometry.
The key geometric relationship that has underpinned
the study of fault growth since the 1980s is
the relationship between fault maximum displacement
(D) and fault length (L) as defined by Elliott
(1976) and Watterson (1986). This relationship is
expressed as D a Ln
. The value of the exponent n
in this relationship has been a topic for discussion
for the last 30 years and values ranging between
0.5 and 2.0 have been advocated (e.g. Walsh &
Watterson 1988; Cowie & Scholz 1992; Schultz
et al. 2008). The range of values reflects the natural
variation between different areas and uncertainties
in data quality and sampling (Gillespie et al.
1992; Kim & Sanderson 2005). Irrespective of the
value of the exponent, the recognition of a positive
correlation between displacement and length suggests
that faults grow progressively as their displacement
increases (Watterson 1986; Walsh &
Watterson 1988).
Since the late 1990s, several studies have been
performed in areas where the rate of sedimentation
exceeds the fault displacement rate, so that acrossfault
changes in the thickness of growth strata
provide a record of the surface trace length and
displacement distribution of faults through time
(Morley 1999; Walsh et al. 2002; Childs et al.
2003; Paton 2006). These studies have shown that
evidence for the propagation of normal faults in
the geological record is often difficult to find and,
in many cases, it appears that the lengths of faults
are formed instantaneously within the time resolution
of the data. If this is true, then the positive
correlation between displacement and length does
not define a trend along which individual faults
grow. Instead, faults would establish their lengths
very early in their development, with initially very
low ratios of displacement to length that increase
rapidly as displacement accumulates. Which of
these models of fault growth is correct remains a
matter for debate, as reflected in the content of
this volume.
This introduction does not provide a comprehensive
review of the literature on this topic, but
aims to outline the current models for the growth
of faults as a backdrop to the collection of papers
in this volume. In the following section, we provide
an in-depth description of current models of fault
growth. We then discuss the methods by which
these can be investigated, highlighting how geometric
observations provide constraints on fault growth
with reference to the papers published in this
volume.
In: The Geometry and Growth of Normal Faults. (Edited by Childs, C., Holdsworth, R. E., Jackson, C. A.-L., Manzocchi, T., Walsh, J. J. & Yielding, G.). Geological Society of London, Special Publication 439, doi.org/10.1144/SP439.23.