Experimental designs to model along-strike fault interaction

J. H. Le Calvez, and B. C. Vendeville

We review the different designs and results of various previous models simulating the along-strike interaction between laterally offset faults, focusing on the formation of pull-apart basins in between strike-slip faults or relay zones located between laterally offset normal faults.

The design of most models traditionally includes the use of a basal sheet, whose edge acts as a velocity discontinuity onto which faults nucleate (Faugère and Brun, 1984; McClay and Ellis, 1987; Vendeville, 1991). One drawback of such design is that the location and orientation of faults in the relay zone are conditioned by the shape of the edge of the basal sheet. An improved version of this design by Sims et al. (1999) using a strong viscous basal layer also forces faults to follow the basal velocity discontinuity. Using a third design by Le Calvez and Vendeville (1996), faults can freely propagate above a thin, weak viscous layer but fault blocks cannot subside or rotate in response to deformation. We introduce a new design in which although fault location is controlled by small instabilities at the brittle-ductile interface, faults can freely propagate along strike after they have nucleated. This design also allows fault blocks to subside, rise, or rotate in response to deformation. The main advantage of such design is that it forces the faults to form at a predetermined location. The ridges are high enough (about one 20th of the brittle-layer thickness) to act as instabilities that trigger the nucleation of the main two faults, which thereby form with an initial lateral offset. But the ridges are low enough so that, once faults have formed in the brittle layer the fault planes act as dominant instabilities and freely propagate along strike. Because this design provides much more freedom for fault interaction within the relay zone and for fault-block rotation, results significantly differ from those of previous models.