Abstract - The limited vertical resolution of reflection seismic
data results in sub-resolution structures accommodating appreciable ductile
strains which should be taken into account in structural restoration and
balancing and in analysis of fault displacements. Non-ductile strains are
expressed as discontinuities, such as fault offsets. A fault map of an
intensively mined coal-seam is used to demonstrate the role of structures
which would not be detected by a typical offshore seismic survey. Four
examples are given of interpretations of seismic datasets in which significant
ductile strain can be demonstrated; (i) an array of normal faults in which
significant extension is accommodated by sub-seismic faults, (ii) a relay
zone in which ductile shear strain accommodates significant displacement
and change of bed-lengths, (iii) an intersection zone between conjugate
normal faults which is effectively a zone of ductile pure shear strain
with horizontal extension, and (iv) a hangingwall fold which accommodates
appreciable ductile displacement and ductile bed extension. In all these
cases the ductile strains and displacements can be estimated from the seismic
interpretation. Unless ductile strains are incorporated in restorations
bed lengths will not balance. Balancing nevertheless remains the prime
method for detection of grossly invalid sections.
In: Modern developments in structural interpretation, validation
and modelling (edited by Buchanan, P. G. & Nieuwland, D. A.) Geological Society of London, Special Publication 99, 27-40,
1996.