Low-angle detachment faults are key to our understanding of the tectonic
evolution of magma-poor rifted continental margins. In seismic images
of present-day rifted margins the identification and interpretation
of such features is, however, notoriously difficult and ambiguous.
We address this problem by studying the structure and seismic response
of such faults through a synoptic interpretation of petrophysical
data and geological evidence from the distal segments of the present-day
West Iberian and the ancient Tethyan margins. On the basis of the
geologically well-constrained remnants of the Tethyan margins, which
are spectacularly preserved and exposed in the Alps of Eastern Switzerland,
vertical profiles at four key geological settings of a typical magma-poor
rifted margin are constructed and their synthetic seismic responses
are compared to the observed seismic data from corresponding locations
in the present-day Iberian margin. The seismic structure of these
profiles is considered as the sum of deterministic large-scale and
the stochastic small-scale components. Both components are analyzed
for all pertinent lithologies. The large-scale structures are derived
from laboratory measurements on samples from both, the West Iberian
and Tethyan margins, whereas the small-scale fluctuations are constrained
predominantly on the basis of well-log data from the Iberian margin.
Different realizations of the simulated stochastic small-scale velocity
fluctuations illustrate the potential variability of impedance contrasts
and its impact on the seismic response from lithological interfaces
and fault structures. Our results indicate that the nature of the
seismic response from low-angle detachment faults is largely determined
through the fracture-healing behavior of the surrounding rocks. Geological
evidence from the exposed fragments of the Tethyan margins indicate
that fracture-healing is generally well developed in crustal lithologies,
but largely absent in mantle lithologies. It is for this reason that
low-angle, intra-crustal detachment faults tend to be seismically
undetectable. Conversely, crust-mantle detachments have a complex
and variable seismic response, depending on the nature of the damaged
zone and on the frequency content of the seismic data. These model-based
inferences are consistent with the available evidence from the present-day
Iberian passive margin and thus open new perspectives for the interpretation
of the corresponding seismic images.