Available data clearly indicate the inactivity of the external compressional front of the northern Marche Apennines in the last 800 ka [e.g. Di Bucci and Mazzoli 2002; Di Bucci et al. 2003]. Surface geological data show that the study area is instead characterised by middle Pleistocene-Holocene normal faulting related with ENE-WSW extension. Comparable inferences can be drawn from geomorphologic data. On the other hand, available focal mechanisms indicate a dominant NNW-SSE oriented compression and the activity of roughly ENE-WSW striking reverse faults. No faults with this strike and kinematics have been detected in outcrop. However, within the framework of the generalised, significant uplift governing the late Quaternary evolution of the study area, NE-SW to ENE-WSW trending sectors characterised by differential uplift have been identified based on geomorphic analysis [e.g. Elmi et al. 1987; Dramis 1992; Fanucci et al. 1996]. It could be speculated that active faults in the study area are mainly represented by lateral/oblique thrust ramps generated in Mio-Pliocene times and presently buried beneath Plio-Pleistocene syn- and post-orogenic deposits.
These fault segments are in fact suitably oriented for reactivation in a stress field characterised by a sub-horizontal maximum compressional (P) axis oriented about NNW-SSE as suggested by seismological data described above. Moreover, a dominant NNW-SSE oriented compression is also envisaged to occur a few tens of kilometres to the south, in the Monte Conero area [E. Tondi, pers. comm. 2003].
These main features of the stress field, although with spatial permutations of the principal stress axes, appear to characterise not only the study area, but also most of the outer Apennines and the related Apulia-Adria foreland during the whole middle Pleistocene-Holocene time span (outer Northern Apennines: e.g. Bertotti et al. 1997; Ghiselli and Martelli, 1997; Morelli and Costa 1997; Piccardi et al. 1997; outer Central-Southern Apennines and Apulia-Adria foreland: e.g. Console et al. 1989; Favali et al. 1993; Alessio et al. 1995; Mancini et al. 2003; Di Bucci and Mazzoli 2003). A NNW-SSE oriented compression is also in good agreement with the stress field related to the Friuli seismicity [Peruzza et al. 2002, and references therein]. All these data suggest a coherent behaviour of the Apulia-Adria foreland within the framework of Africa-Europe geodynamics [Mazzoli and Helman 1994; Ward 1994; Di Bucci and Mazzoli 2002; Hollenstein et al. 2003].