3D Geometry of normal faults in a rheologically layered system : Analogue modelling and seismic examples
Résumé
Geometry of normal faults, within the sedimentary cover, may be influenced
by different parameters such as the presence, position and efficiency
of décollement levels, the amount, direction and velocity of extension,
and the rate of synkinematic sedimentation. These parameters
have already been studied at different scales in field approach, analogue
and numerical modelling. The effect of several décollement levels has
been studied at lithospheric scale to better understand the deformation
processes between surface and depth. At the scale of single structure in
a sedimentary basin, previous analogue modelling only studied the effect
of a determined geometry of a fault on the synkinematic sedimentation.
Here we used analogue modelling to analyse the 3D geometry of a
single structure in a domain with three prekinematic décollement levels,
analogue of salt, shale or under-compacted level. These experiments result
in flat and ramp geometry in relation with décollement level and
the pattern of the deformation depends here mainly on the velocity and
amount of extension. The results of the experiments were compared to
seismic examples in order to better interpret typical fault setups. One
of the key points is that the geometry of normal faults displays large
variations both in direction and dip, only in pure extensive regime, related
to the presence of décollement levels, and not associated with any
global/regional variation of extension direction.