Pleistocene changes in the central Apennine fault kinematics: A key to decipher active tectonics in central Italy

Abstract

Integrated structural, geomorphological, and stratigraphic data have permitted the definition of the Quaternary structural evolution of some tectonically generated basins in the central Apennines. Available data indicate that some N130°-140°trending Quaternary normal faults have not been active since the middle Pleistocene, while along some other faults with the same trend, left-lateral strike-slip or oblique-slip movements are superimposed on normal movements. Pure normal movements were found to affect only N125°to E-W trending faults. This structural evolution indicates that fault kinematics in the central Apennines changed markedly between the early and middle Pleistocene. Current models infer that this change may have been a response to the bending which caused the arcuate shape of the Apennine orogen. The deformation related to the bending added to the effects of the regional stress field. As a result, post early Pleistocene fault kinematics were due to an extension that locally was not perfectly perpendicular to the inherited normal faults and that is consistent with models of oblique-slip tectonics. Processes of arc formation and related 'incompatibility' between inherited Quaternary faults and post Early Pleistocene extension have significant implications regarding research on active tectonics. In fact, some nonactive faults show misleading features typical of recent activity while some active faults are poorly visible owing to the recent age of the present regime. This kinematic evolution therefore represents one of the major factors (others being the low slip rates and the fragmented structural setting) which hinders the definition of reliable active faulting schemes for the Apennine chain.