INTERACTIONS BETWEEN NORMAL FAULT GROWTH AND SURFACE PROCESSES: INSIGHTS FROM COUPLED TECTONIC AND LANDSCAPE EVOLUTION MODELLING

Recent fault studies highlight the need for a more detailed picture of how fault evolution, and more particularly interaction between faults, influences the development of sediment transport systems in actively deforming regions. Numerical models have proved valuable tools to investigate the interactions between the various transport and tectonic processes over geological timescales. However, no previous work using surface process models (SPMs) has explicitly considered the impact of fault propagation and interaction on the developing landscape.

We investigate the impact of interaction between normal faults on the developing topography by coupling a realistic fault propagation model (Cowie, 1998: J. Struct. Geol. 20(8), 1075-87) with the 3D numerical surface process model, CASCADE. Model runs were carried out using a moderately high resolution grid on a variety of scales (<300m to 2km average node spacing) to investigate landscape evolution over a few to tens of kilometres. The tectonic system is unique in that it explicitly models interaction and particularly stress feedback between many propagating faults, allowing the evolution of a complex fault pattern to be investigated. CASCADE incorporates sediment transport via long range (fluvial) and short range (diffusional hillslope) processes as well as a stochastic landsliding algorithm. The complex fault topography can be introduced thanks to the unique triangulation method used by CASCADE.

This work builds on our previous studies investigating the influence of simple fault geometries on evolving topography and sediment distribution networks. Drainage systems are seen to respond to fault growth by deflection, backtilting (stream reversal), incision and the headward propagation of knickpoints. Model results clearly demonstrate that stress feedback between faults, leading to enhanced and retarded rates of fault growth, is an essential factor in reproducing the drainage patterns and topography seen in active extensional settings.