Influence of lateral heterogeneities on strike-slip fault behaviour: insights from analogue models

Abstract

This study investigates how lithological changes can affect the strike-slip fault propagation patterns using analogue models. Strike-slip fault zones are long structures that may cut across pre-existing tectonic or lithological steep boundaries. How strike-slip faulting is affected by a laterally heterogeneous upper crust is crucial for understanding the evolution of regional and local fault patterns, stress reorientations, and seismic hazard. Our models undergo sinistral distributed strike-slip shear (simple shear) and have been analysed by particle image velocimetry (PIV). We use quartz sand and microbeads as brittle analogue materials over a viscous mixture to distribute the deformation through the model. The first models investigate strike-slip faulting in a homogeneous upper crust using quartz sand or microbeads only. Three further models examine how the presence of a central section which laterally differs in its properties influences strike-slip faulting. The main observations are the following: The homogeneous upper crust shows typical Mohr–Coulomb strike-slip faults, with synthetic fault strikes related to the angle of internal friction of the material used. The heterogeneous upper crust has a profound effect on synthetic fault propagation, interaction, and linkage, as well as the kinematic evolution of antithetic faults that rotate around a vertical axis. The orientation of the central section determines whether antithetic fault activity concentrates along the entire length of the central contact or not. In the first case, fault activity is segmented or the number of different faults formed is increased in distinct domains. In the second case, the properties of the central material determine fault propagation, interaction, and/or linkage across the central domain. These findings have potential implications for nature that have been seen in the NW Iberian Peninsula. In this area, the change in direction of the sinistral faults and the position of the antithetic faults can be explained due to lithological change.