Comparison of normal fault slip to long-term landscape building. Insights from morphometry analysis and geochronological data on the Magnola-Velino fault system (central Apennines, Italy)

Active faults play a major role in relief building, partly through the accumulation of vertical co seismic displacement during major earthquakes. Triangular facets are geomorphic features recording normal fault cumulative displacements on relatively long time scales (10-100ka). To unravel the relationships between the rate at which slip accumulates on a fault scarp and the long-term evolution of triangular facets, we have to acquire quantitative datasets on normal fault slip rates at various timescales and rates of erosion of the facets.

Here we present a study on facet build-up over 10-100 ka time range in the central Apennines in Italy. The normal fault systems that control the present tectonic activity of the range are very well studied with numerous detailed paleoseismological records. We focus on the Magnola-Velino fault system which displays well preserved triangular facets and accurate chronological constraints on the 10-20m high fault scarp located at the base of the facets. We combine high resolution morphometric analysis (gullies steepness, facets slope and others), using Digital Elevation Models derived from Pléiades imagery and a new dataset for cosmogenic nuclides concentration (³⁶Cl) including 54 bedrock samples on 9 gullies and facets profiles above the scarps. Magnola-Velino fault system is 20-25km long, and morphometric parameters such as steepness index display a systematic evolution along strike. First measured ³⁶Cl concentrations, on Magnola, range from 6 to 50 x10⁴ at/g on gullies and 50 to 150 x10⁴ at/g on facets, with systematic variations along strike. We document the joint evolution of geochronological data and morphological parameters for this fault system and compare it with existing constraints on long-term slip rate.