The role of pre-existing discontinuities in the development of extensional faults: An analog modeling perspective. (May 2015) - Bonini, Lorenzo
Abstract: Several mountainous regions are currently affected by syn- or post-orogenic active extension. We investigate how a newly-formed normal fault interacts with structures inherited from a previous contractional phase. To this end, we use analog models that adopt an innovative technique for performing a precut that mimics such inherited structures into a clay layer; this clay layer is laid on top of a master fault simulated by two rigid blocks sliding along an inclined plane. We carry out six experiments with variously oriented precuts and compare the results with those obtained in a reference isotropic experiment. All other conditions are identical for all seven realizations. Fault evolution is monitored by taking closely-spaced snapshots analyzed through the Digital Image Correlation method. We find that the upward propagation of the normal fault can be either accelerated or decelerated depending on the presence of a precut and its orientation. Such precuts can also promote or inhibit the formation of bending-moment faults. These interactions between master fault and precut also affect the shape of the fault-related syncline–anticline pair. Highlights: Analysis of normal faults that form in areas previously affected by contractional tectonics. New normal faults inevitably interact with inherited faults during their development. We use analogue models with precuts in wet kaolin to simulate pre-existing faults. We found that development of normal faults and related structures depends on the orientation of pre-existing faults.