Methods for determining the Pleistocene-Holocene component of displacementon active faults reactivating pre-Quaternary structures: examples-from theCentral Apennines (Italy)

In the tectonically active fault system of the Central Apennines,Ridge (Ita ly) several normal/ transtensive faults mapped as Quaternary structures sho w evidence Of pre-Neogene thrusting activity. Therefore, determining the am ount of fault-slip during Pleistocene-Holocene times is crucial for seismic hazard assessment. Three principal lines of evidence have been used in thi s study for estimating the pre-Quaternary activity of extensional fault sys tems in the Central Apennines. The first is the geological and stratigraphi c record (i.e. thickness and facies variations) for pre-quaternary successi ons. The second is the widespread structural analysis evidence of extension al faults involved in Neogene thrust tectonics; whether considering a passi ve role (e.g. fault carried and tilted above a thrust-sheet) or inversion ( e.g. positive inversion and related minor structures). The third is the geo morphological evidence, particularly erosion surface analysis, which permit s the understanding of the relief generated by tectonics after the formatio n, of post-thrusting erosional surfaces. Preliminary results from some faul ts which belong to the Sibillini Mts.: and the Norcia extensional fault zon es show clear evidence of Quaternary reactivations. (C) 1999 Elsevier Scien ce Ltd. All rights reserved.