Propagation of an inherited strike-slip fault through a foreland-chain system: quantitative aspects from analogue modeling and applications

Giovanni Toscani(*), Daniela Di Bucci(**), Antonio Ravaglia(***), Silvio Seno(*), Umberto Fracassi(****) & Gianluca Valensise(****)
(*) Dipartimento di Scienze della Terra, Università di Pavia, Via Ferrata, 1 - 27100 Pavia, Italy. Tel. +39 0382 985857 - Fax +39 0382 985890 - e-mail: govanni.toscani@unipv.it (**) Dipartimento della Protezione Civile, Via Vitorchiano, 4 - 00189 Roma, Italy. (***) PetroSA, 151 Franns Conradie Drive, Parow 7500, Republic of South Africa. (****) Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata, 605 - 00143 Roma, Italy

We investigated quantitatively the propagation of a reactivated strike-slip fault through a sedimentary cover. To this end we prepared five simplified analogue models that reproduce a chain with its frontal allochtonous wedge overrunning the foreland. The foreland/chain deformation follows the reactivation of an inherited strike-slip fault cutting the foreland domain. The observation and quantification of the effects of this reactivation, in particular on the orogenic wedge front, provide new insight on the evolution of this type of tectonic setting. We placed special emphasis on quantifying the structural features observed in the models to (1) interpret the kinematics of the reactivated shear zone, and (2) put forward hypotheses on areas indirectly affected by the reactivated fault. The interpretation of the models was based on an integrated analysis of surface and subsurface data. The results show that the geological setting is strongly influenced by the presence of a reactivated pre-existing lineament, that ultimately controls the development and pattern of newly-formed faults. Finally, we present and discuss two natural examples (in Italy Molise-Gondola shear zone, Southern Apennines, and Scicli-Ragusa line, Sicily) in view of the modeling results.

Fault reactivation, foreland, orogenic wedge, sandbox models, quantitative analysis.