A Numerical Investigation of Drainage Network Evolution During Fault Interaction and Linkage

We have coupled together a numerical fault growth model and a surface process model (CASCADE; Braun and Sambridge, Basin Research, 9, 27-52, 1997) to study the way in which drainage basin geometry and river long profiles respond to the progressive formation and linkage of an underlying fault network. The numerical fault growth model simulates nucleation, propagation and displacement accumulation on a population of steeply dipping extensional faults. Elastic interaction between faults is included, resulting in significant displacement rate variations in space (along neighbouring fault segments) and through time. The most significant temporal variations in slip rate are those associated with fault linkage events in which the linking fault segments experience increased rates of slip while adjacent faults in foot-wall and hanging-wall areas become inactive. The size, elevation and lateral continuity of topographic uplifts (footwall highs) and depocentres (hanging-wall lows) vary through time as the faults grow and link. The faults appear as sub-vertical scarps that can grow in height and length through time. Fluvial erosion, diffusive hill-slope processes, landsliding, lake formation and sediment deposition are all included in the surface process model. Orographic effects are not considered. The tectonic model outputs maps of elevation change. These maps are input sequentially into the surface process model to drive tectonic elevation changes while erosion and deposition are ongoing. The spatial and temporal scales of the coupled model have been chosen to correspond with an area of active extensional faulting in Lazio-Abruzzo, Italy. Normal fault development in this area during the last 3 Myrs has resulted in interaction and incipient linkage between several fault segments that vary in length from 20 to 40 km, within a ~150 km long fault array. For this area we have river long profiles derived from a high-resolution DEM, and field measurements of river channels crossing faults that have experienced a temporal variation in throw rate. These data will be compared directly with outputs from the coupled numerical model.